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Pelvic Drop Changes due to Proximal Muscle Strengthening Depend on Foot-Ankle Varus Alignment

Pelvic Drop Changes due to Proximal Muscle Strengthening Depend on Foot-Ankle Varus Alignment Hindawi Applied Bionics and Biomechanics Volume 2019, Article ID 2018059, 12 pages https://doi.org/10.1155/2019/2018059 Research Article Pelvic Drop Changes due to Proximal Muscle Strengthening Depend on Foot-Ankle Varus Alignment 1 1,2 1,2 Aline de Castro Cruz , Sérgio Teixeira Fonseca , Vanessa Lara Araújo , 1 1 1 Diego da Silva Carvalho, Leonardo Drumond Barsante, Valéria Andrade Pinto , 1,2 and Thales Rezende Souza Graduate Program in Rehabilitation Sciences, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil Department of Physical Therapy, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil Correspondence should be addressed to Thales Rezende Souza; thalesrs@ufmg.br Received 30 November 2018; Revised 11 March 2019; Accepted 21 March 2019; Published 12 May 2019 Academic Editor: Craig P. McGowan Copyright © 2019 Aline de Castro Cruz et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Strengthening of hip and trunk muscles can modify pelvis and hip movements. However, the varus alignment of the foot-ankle complex (FAC) may influence the effects of muscle strengthening, due to the relationship of FAC alignment with pelvic and hip kinematics. This study evaluated the effects of hip and trunk muscle strengthening on pelvis and hip kinematics during walking, in subgroups with larger and smaller values of FAC varus alignment. In addition, this study evaluated the effects of hip and trunk muscle strengthening on hip passive and active properties, in the same subgroups. Methods. Fifty-three women, who were divided into intervention and control groups, participated in this nonrandomized controlled trial. Each group was split into two subgroups with larger and smaller values of FAC varus alignment. Hip and trunk muscle strengthening was performed three times a week for two months, with a load of 70% to 80% of one repetition maximum. Before and after strengthening, we evaluated (1) pelvis and hip excursions in the frontal and transverse planes during walking, (2) isokinetic hip passive external rotator torque, and (3) isokinetic concentric and eccentric peak torques of the hip external rotator muscles. Mixed analyses of variance (ANOVAs) were carried out for each dependent variable related to walking kinematics and isokinetic measurements (α =0 05). Results. The subgroup with smaller varus alignment, of the intervention group, presented a reduction in pelvic drop after strengthening (P =0 03). The subgroup with larger varus alignment increased pelvic drop after strengthening, with a marginal significance (P =0 06). The other kinematic excursions did not change (pelvic anterior rotation P =0 30, hip internal rotation P =0 54, and hip adduction P =0 43). The intervention group showed increases in passive torque (P =0 002), peak concentric torque (P <0 001), and peak eccentric torque (P <0 001), independently of FAC alignment. These results suggest that FAC varus alignment influences the effects of strengthening and should be considered when hip and trunk muscle strengthening is used to reduce pelvic drop during walking. 1. Introduction hip external rotators and abductors may increase passive and active (eccentric) mechanical resistance against hip Strengthening of hip and trunk muscles has been used to internal rotation and adduction [3, 4, 10]. In addition, modify pelvis and hip excessive movements [1–4] since they strengthening of trunk rotators and lateral flexors may may be involved in the production of injuries of the hip [5, increase passive and eccentric resistance against pelvic drop 6] and the lumbopelvic complex [7]. Pelvic drop, axial rota- and axial rotation [3, 4, 8, 9]. Gains in concentric strength of these muscles could also facilitate the production of hip tion, hip adduction, and hip internal rotation occur in the first half of the stance phase of walking [8, 9]. Muscle external rotation and abduction, as well as pelvic raise. These strengthening may be used in an attempt to reduce ampli- movements take place subsequently in the second half of the tude of these motions. For example, strengthening of the stance phase [9]. Despite these theoretical benefits, previous 2 Applied Bionics and Biomechanics 25 kg/m studies have demonstrated no effects of hip strengthening on to facilitate palpation of anatomical landmarks for the kinematics [11] and kinetics [12] of the pelvis and hip the kinematic model creation; (4) absence of self-reported during walking. musculoskeletal symptoms or injuries in the last three Biomechanical characteristics other than the active and months, to prevent the impact of pain and previous injury passive functions of the hip and trunk muscles could influ- on the assessed movement pattern; (5) no practice of physical ence lower limb kinematics in weight-bearing tasks [10, 13] exercise in the last three months, to remove possible con- and affect the kinematic changes produced by the strength- founding effects of other physical exercises on the strength- ening. Varus alignment of the foot-ankle complex (FAC), ening protocol used in this study; and (6) presence of measured in non-weight-bearing, constitutes a biomechani- normal range of motion of hip internal rotation (from 34 ° ° ° cal factor that influences the magnitude of FAC pronation to 71 ) and hip external rotation (from 25 to 56 ) [22]. Peo- during walking [14, 15]. By its turn, the magnitude of FAC ple with hip internal and external rotation restrictions could pronation during weight-bearing tasks may influence hip have difficulties to perform the strengthening exercises prop- and pelvis kinematics [16–20]. Higher FAC pronation values erly. In addition, these individuals might also have anatomi- are related to higher magnitudes of hip internal rotation and cal abnormalities such as anteversion or retroversion of the adduction [17–20] and pelvic drop [16, 19]. Therefore, the femoral neck, which could influence changes in hip kinemat- magnitude of FAC varus alignment (and the magnitude of ics after muscular strengthening. The exclusion criteria were FAC pronation) may be an individual biomechanical charac- (1) adherence lower than 80% of the training sessions of the teristic that influences the effects of muscle strengthening on strengthening program. The time needed for hypertrophy changing pelvis and hip motions. For example, larger values gains in the lower limbs of women is about six weeks, after of FAC varus alignment may result in greater FAC pronation the beginning of training, which corresponds to 80% of the [14, 15] and produce greater hip adduction and pelvic drop duration of the training protocol used in our study [23]; (2) [16–20] during walking. Thus, the presence of larger varus engagement in physical exercise during the study period, could make it difficult to produce an amplitude reduction to prevent possible confounding effects of other physical of these motions, after proximal muscle strengthening. exercises on the strengthening protocol used in this study The objective of this study was to investigate the influ- (physical exercise was considered as the practice of activities ence of FAC varus alignment on possible changes resulting or training aiming to improve physical fitness or health); (3) from muscle strengthening at the hip (mainly abductors inability to keep the hip muscles relaxed during the passive and lateral rotators) and trunk (mainly abdominals and latis- torque test; and (4) presence of pain during the assessments simus dorsi). We considered possible changes in (1) the and inability to perform the tests correctly. motion excursions of the pelvis and hip in the frontal and FAC varus alignment measurements were performed in transverse planes, during gait, and (2) hip muscle strength both lower limbs of the participant. Allocation in the control and passive torque. The main study hypotheses were that a and intervention groups was performed according to the subgroup with larger FAC varus alignment would have availability of participants to perform the intervention. For smaller or no reductions in the excursions of pelvis and hip allocation in the larger and smaller FAC subgroups, the motions. Changes in hip strength and passive torque were control and intervention groups were divided in relation to also investigated to help understand possible kinematic varus values by means of the 50th percentile. However, in effects. A secondary study objective was to verify if individ- order to guarantee that the varus alignment values were sim- uals with larger FAC varus alignment have larger foot prona- ilar between the control and intervention groups, it was tion during walking, as previously observed [14, 15]. necessary to match the groups according to varus values. Thus, the participants from the intervention group were eval- uated, and the definition of which limb should be analyzed 2. Methods was random (drawing). For the control group, the varus 2.1. Participants. Fifty-three women, who were divided into alignment was evaluated in both limbs, and the limb analyzed intervention and control groups, participated in this nonran- was selected to match the varus value of a participant from domized controlled trial. Both groups were divided into the intervention group. This matching procedure was done to guarantee that the subgroups from the intervention and subgroups of larger and smaller varus magnitudes. The par- ticipants were selected by means of convenience sampling. control groups were similar according to the magnitude of The number of participants was calculated based on an FAC varus. expected moderate effect size (f =0 3), with a level of signifi- Initially, fifty-six women were included in the study. The cance of 0.05 and a desired statistical power of 0.80. Accord- participants signed an informed consent form to participate in the study. The intervention group (n =26) was divided ing to this analysis, approximately 58 individuals would be needed. This study was approved by the institution’s into two subgroups: one with smaller varus alignment Research Ethics Committee (CAAE–0427.0.203.000-11). (n =13) and another with larger varus alignment (n =13). The control group (n =27) was also split into subgroups with The inclusion criteria were (1) female, since women pres- ent greater pelvic drop and hip adduction compared to men smaller varus alignment (n =14) and larger varus alignment (n =13) (Figure 1). The groups were divided according to [19, 20] and may be more frequently subjected to interven- tions intended to reduce pelvic and hip motions; (2) age the median varus alignment values to equally separate them between 18 and 35 years, to avoid the impact of age on hyper- into subgroups of larger and smaller varus alignments. In trophy [21]; (3) body mass index (BMI) less than or equal to addition, this division also allowed to investigate whether Applied Bionics and Biomechanics 3 Assessed for inclusion criteria (n = 111) Not meeting inclusion criteria (n = 55) Participated in the study (n = 56) Intervention group (n = 28) Control group (n = 28) SVI (n = 14) e LVI (n = 14) SVC (n = 14) e LVC (n = 14) Excluded for not performing at least 80% of Excluded for having started the practice of training (n = 1) physical exercise (n = 1) Control group (n = 27) Intervention group (n = 27) SVI (n = 14) e LVI (n = 13) SVC (n = 14) e LVC (n = 13) Variables: Variables: - Kinematics and hip active torque - Kinematics and hip active torque Intervention group (n = 26) Control group (n = 27) SVI (n = 13) e LVI (n = 13) SVC (n = 14) e LVC (n = 13) Excluded due to technical problems in kinematic data (n = 1). - Hip passive torque - Hip passive torque Intervention group (n = 25) Control group (n = 26) SVI (n = 13) e LVI (n = 12) SVC (n = 13) e LVC (n = 13) Excluded due to atypical pattern of the passive Excluded due to atypical pattern of the passive torque curve (n = 1) and due to technical torque curve (n = 1) problems in kinematic data (n = 1) Figure 1: Flow diagram showing the number of participants at each stage of the study. LVI: larger varus in the intervention group; SVI: smaller varus in the intervention group; LVC: larger varus in the control group; SVC: smaller varus in the control group. the varus values of the subgroups are associated with FAC values of the forefoot-shank angle as larger values of FAC pronation amplitude during gait. varus alignment. The mean of three forefoot-shank angle Independent t-tests showed that FAC alignment values measures was calculated and used for analysis. The were significantly different between the subgroups of the intraexaminer reliability of this measure was evaluated intervention group (P <0 001) and between the subgroups with ten individuals who performed two evaluations with a of the control group (P <0 001). The smaller varus sub- one-week interval, and the intraclass correlation coefficient groups, in the control and intervention groups, did not show (ICC) obtained was 0.93. significant differences in varus alignment (P =0 57). The larger varus subgroups, in the control and intervention 2.3. Evaluation of Walking Kinematics. A three-dimensional groups, did not show significant differences in varus align- motion analysis system Codamotion (Charnwood Dynamics, ment neither (P =0 71). The characteristics of the subgroups Rothley, England) was used. Motion of the pelvis, thigh, are indicated in Table 1. shank, rearfoot, and forefoot was captured with clusters of active tracking markers that were placed on each of these 2.2. Evaluation of Foot-Ankle Complex (FAC) Alignment: body segments [4]. Moreover, anatomical markers (two Forefoot-Shank Angle. The FAC alignment was assessed by proximal and two distal markers) were used in each segment means of a clinical measure that combines the varus/valgus for the kinematic model definition [4, 25]. Initially, the par- alignment of the FAC (forefoot, rearfoot, and shank align- ticipant remained in orthostatic position for a static data col- lection of five seconds. The position of the participant’s feet ments) and midfoot inversion mobility [15, 24]. This clinical measure provides the forefoot-shank angle, measured in was drawn on a paper to be reproduced during reassessment. open chain (see Figure S1 in Supplementary Materials). In This static posture data with both tracking and anatomical the present study, for simplification, we considered larger markers was later used to create the kinematic model. After Monitoring of Allocation of Recruitment of Analysis participants participants participants 4 Applied Bionics and Biomechanics Table 1: Characteristics of the subgroups. Age (years) BMI (kg/m ) FAC varus ( ) Groups Subgroups Evaluated limb Mean (SD) Mean (SD) Mean (SD) Left (n =7) Smaller varus 21 (2.95) 20.80 (1.57) 9.51 (4.44) Right (n =6) Intervention Left (n =7) Larger varus 23 (3.88) 21.39 (2.24) 22.08 (4.68) Right (n =6) Left (n =2) Smaller varus 22 (1.73) 20.63 (2.10) 10.54 (4.75) Right (n =12) Control Left (n =7) Larger varus 21 (1.97) 21.31 (2.10) 21.45 (3.79) Right (n =6) SD: standard deviation; BMI: body mass index; FAC: foot-ankle complex. analyzed trials was due to an uneven number of marker losses the static data collection, the participant walked on an electric treadmill (ProAction G635 Explorer, BH Fitness; among the subjects. However, none of the subjects had less Vitoria-Gasteiz, Alava, Spain) with the tracking markers than 10 trials included in the analysis [29]. only. Thirty consecutive walking cycles were collected at a Motion excursions during the stance phase of walking sampling rate of 100 Hz. The participant was asked to walk were calculated for pelvic anterior rotation (transverse plane), at her self-selected comfortable speed, in the first evaluation. pelvic drop (frontal plane), hip internal rotation (transverse The same speed was used in the reevaluation (i.e., after the plane), and hip adduction (frontal plane). Motion excursion intervention period). The mean and range of speed of the was computed as the difference between the angle obtained subgroups were as follows: smaller varus intervention group in the first frame of stance (i.e., at initial contact) and the peak (3.08 km/h (SD 0.73), 2.00 to 4.00), larger varus intervention angle within the stance phase. For statistical analyses, the group (3.15 km/h (SD 0.59), 2.00 to 4.00), smaller varus con- outcome variables were the average excursions obtained from trol group (3.07 km/h (SD 0.55), 2.00 to 3.50), and larger the included trials of each participant. Rearfoot-shank and varus control group (2.73 km/h (SD 0.52), 2.00 to 3.50). An forefoot-shank eversion excursions (frontal plane) were cal- initial statistical analysis was done to verify if the velocities culated only for the prestrengthening evaluation, since these were different among the subgroups. A two-way ANOVA variables were used only to verify if individuals with larger was performed with the factors group (control and interven- varus alignment show greater FAC pronation during walking. tion) and varus alignment (smaller and larger). Since the The test-retest reliability of all outcome variables (i.e., velocity was exactly the same in the evaluation and reevalua- excursions of the pelvis, hip, rearfoot-shank, and forefoot- tion, the condition was not a factor for this analysis. The shank motions) was evaluated in a pilot study with ten par- interaction group × varus alignment revealed that the veloc- ticipants in two evaluations with a one-week interval. This ity was not different among the subgroups (P =0 analysis showed moderate to good reliability (intraclass cor- 214). Visual 3D software (C-Motion Inc., Rockville, Maryland, relation coefficients ranging from 0.77 to 0.89). USA) was used to process the kinematic data. The data were 2.4. Isokinetic Evaluation: Passive Torque and Hip Muscle filtered with a fourth-order, Butterworth, zero-lag, low-pass filter, with a cut-off frequency of 6 Hz. From the static Strength. Hip passive torque and muscle strength were mea- posture data, a rigid body kinematic model of six degrees of sured with an isokinetic dynamometer Biodex 3 Pro (Bio- freedom was created [25–27] and applied to the walking trial. dex Medical Systems, Shirley, USA) at a sampling rate of The pelvis angle (pelvic motion in relation to the global coor- 100 Hz. During passive hip measurement, the dynamometer was in the passive mode, and a surface electromyography dinate system) and hip angle (thigh motion in relation to the pelvis) were calculated in the frontal and transverse planes system (ME6000, Mega Electronics Inc., Kuopio, Finland) during the stance of walking. Furthermore, rearfoot-shank was used to ensure that hip muscles were relaxed. Electro- and forefoot-shank angles (rearfoot and forefoot motions myographic data were collected at a sampling rate of in relation to the shank) were calculated in the frontal 1000 Hz and recorded using the MegaWin 3.0 software (Mega Electronics Inc., Kuopio, Finland). Active surface elec- plane during the stance of walking. These angles were cre- ated with the following Cardan sequence: lateral-medial, trodes were placed on the following muscles: gluteus maxi- anterior-posterior, and superior-inferior [25]. mus, gluteus medius, biceps femoris, tensor fascia lata, and The stance phase of walking was defined as the period adductor magnus [30]. from the instant the calcaneus contacted the ground until For the measurement of the hip passive torque during internal rotation, the participant was positioned in prone, the instant the toes left the ground. These events were estab- lished by two examiners who concurrently observed the ante- with the knee flexed at 90 and the tibial tuberosity aligned roposterior displacement curves of rearfoot and forefoot with the axis of rotation of the isokinetic dynamometer. tracking markers [28]. Ten to sixteen walking stance phases The upper limbs of the participant were placed next to the without any marker tracking loss were analyzed for each trunk, and a belt was used to stabilize the pelvis. The equip- participant. This intersubject variation in the number of ment’s attachment moved the participant’s hip from 25 of Applied Bionics and Biomechanics 5 and the poststrengthening evaluation was two months, with a external rotation to 25 of internal rotation, at an angular velocity of 5 /s [4]. The examiner instructed the participant maximum limit of two months and one week. The training to remain relaxed and not to resist and/or assist hip motion days were chosen according to the participant’s availability. during the test. Before the test, five repetitions of the move- The load for the exercises was set at 70% to 80% of one ment were made for tissue viscoelastic accommodation and repetition maximum (1RM) [32], as this load level is rec- participant familiarization. Moreover, electromyographic ommended when hypertrophy is aimed [32]. During the signals of the muscles were recorded with the participant 1RM test, the examiner observed the movement to ensure resting in static position. During the test, three valid mea- that the participant performed the exercise throughout the sures of hip passive torque were performed. At each repeti- full range of motion without compensatory movements tion of the test, the electromyographic data were extracted (i.e., movement components performed by muscles other and processed in MATLAB software (The MathWorks than the muscles being tested). For each exercise of the Inc.). The data was filtered using a fourth-order, Butterworth, protocol, three sets of eight to nine repetitions were per- bandpass filter, with cut-off frequencies of 10 and 500 Hz. formed at moderate velocity (about 3 seconds for the iso- The signal collected during the participant’s rest was com- tonic cycle) with a one-minute rest between sets [32]. pared to the signal obtained during each test. The repetitions The load was increased by 5 or 10% when the participant with muscular activity were defined as those in which the was able to perform three sets of nine repetitions for two con- electromyography signal was equal to or greater than the secutive sessions [32]. In the fifth week, the eccentric training mean plus two standard deviations of the signal captured at of hip external rotators and abductors was increased to 90% rest. When muscle contraction occurred, a new repetition or 100% of 1 concentric RM [33, 34]. Bilateral isotonic of the test was performed. strengthening was performed in full range of motion for the The evaluation of the active maximum concentric and following muscles: (a) hip external rotators, (b) gluteus med- eccentric hip external rotation torques was performed with ius, (c) latissimus dorsi, (d) oblique and rectus abdominis the participant in the same position of the passive torque test, and quadratus lumborum, and (e) hip and trunk rotators except for the upper limbs. The participant was instructed to and extensors in closed kinematic chain [4]. It was expected hold a belt placed under the chair and keep the shoulders and that the strengthening of these muscles could reduce exces- elbows flexed to stabilize the trunk during the test. For famil- sive motion excursions of the pelvis and hip in the frontal iarization, before the test, the participant performed the and transverse planes. Hip external rotators and abductor movement with submaximal force for five repetitions. The muscles could resist hip excessive internal rotation and ° ° tests were performed from 30 of internal rotation to 20 of adduction [8, 9]. The trunk muscles also have the potential external rotation at an angular velocity of 30 /s [4]. During to resist hip adduction and internal rotation [8, 9]. Tension external rotation, the hip muscles contracted concentrically. in the latissimus dorsi muscle can be transmitted to the During internal rotation, the muscles contracted eccentri- gluteus maximus through the thoracolumbar fascia and cally. The participant received instructions and verbal increases hip resistance against internal rotation [35]. The encouragement to produce maximum strength. Three sets oblique abdominal muscles can reduce ipsilateral pelvic drop of five repetitions were performed, and the concentric and and contralateral hip adduction [8, 9]. Therefore, the open- eccentric torques of each repetition were recorded. chain exercises depicted in Figure 2 were chosen to selectively For data reduction, the participant’s shank and foot strengthen the desired muscles. lengths were measured. In addition, a repetition of the test The last exercise (Figure 2(e)) was initiated only in the third week with minimal load (5 kg), aiming to learn the without the participant was performed to record the torque produced by the weight of the equipment’s lever arm. correct execution of the movement. In the fifth week, the load The data obtained by the isokinetic dynamometer were of this exercise was increased to 70% or 80% of 1RM [4]. The processed with a routine developed in MATLAB. The signals purpose of this exercise was to promote a more global were filtered with a fourth-order, Butterworth, low-pass fil- strengthening, for the muscles that can help extend and rotate the hip and trunk. It was performed in a weight-bearing situ- ter, with a cut-off frequency of 1.25 Hz. The torques gener- ated by the shank, foot, and dynamometer’s lever arm ation such as the stance phase of walking. Although this last weights were subtracted from the total torque [4]. exercise was performed in weight bearing, one objective of For the passive torque, the mean torque produced during the present study was to investigate the kinematic effects of the first 20 of hip internal rotation was calculated, in Newton changes in the active and passive functions of the muscles regardless of the exercises being performed in open- or meters (Nm), for each test repetition [4]. This amplitude of hip internal rotation was chosen as an approximation of the closed-chain situations. average range of hip rotation during walking [31]. For the active torques, the peak values of the concentric and eccentric 2.6. Statistical Analysis. Mixed analyses of variance (ANO- torques were calculated for each repetition. For statistical VAs) were carried out for each dependent variable: excursion of pelvic anterior rotation, pelvic drop excursion, hip internal analysis, the mean of the three repetitions was used, for the passive, concentric, and eccentric torques. rotation excursion, and hip adduction excursion; passive hip torque; and concentric and eccentric hip external rotator tor- 2.5. Muscle Strengthening Protocol. Hip and trunk muscle ques. Each ANOVA had two between-subject effects with strengthening was performed three times a week for two two levels (varus alignment: larger and smaller; group: con- trol and intervention) and one within-subject effect with months. The period between the prestrengthening evaluation 6 Applied Bionics and Biomechanics (a) (b) (c) (d) Figure 2: Continued. Applied Bionics and Biomechanics 7 (e) Figure 2: Strengthening exercises of the hip and trunk muscles: (a) hip external rotators, (b) gluteus medius, (c) latissimus dorsi, (d) abdominal oblique and quadratus lumborum, and (e) hip and trunk rotators and extensors in closed kinematic chain. Source: [4]. Table 2: Significance of the kinematic variables for the interactions two levels (condition: pre- and postintervention). Each of interest. mixed ANOVA performed for each dependent variable Group × condition × generated the following interactions of interest: group × Group × condition Variables varus alignment condition and group × condition × varus alignment. When a PF P F significant difference was found in the interaction effect, pre- planned contrasts were used to identify which group and Pelvis frontal 0.95 0.004 0.01 7.12 subgroup comparisons showed significant differences. Pelvis transverse 0.63 0.23 0.30 1.11 After verifying data normality by means of Shapiro- Hip frontal 0.85 0.03 0.43 0.63 Wilk tests, independent t-tests were performed to compare Hip transverse 0.48 0.50 0.54 0.38 the rearfoot-shank eversion angle (data with normal distri- P ≤ 0 05; F: F value for the interaction in mixed ANOVA. bution) between subgroups of smaller and larger varus alignments. Moreover, the Mann-Whitney test was carried out to compare the forefoot-shank eversion angle (data varus, a marginal P value (P =0 06) was observed, which with nonnormal distribution) between subgroups of smaller shows a tendency of increase in pelvic drop during walking and larger varus alignments. For all analyses, a type 1 error (Table 3). In addition, both control groups with smaller and probability of 5% (α =0 05) was considered. larger varus alignments did not show significant differences in pelvic drop after eight weeks (P =0 70 and P =0 81, 3. Results respectively). Thus, the intervention group showed a change after the intervention period, for pelvic drop, only when it Descriptive data of all outcome variables are presented in was divided into smaller and larger varus alignment sub- Supplementary Materials (see Table S1). groups. And the same subgroups in the control group did not show any changes. 3.1. Pelvis and Hip Kinematics. ANOVAs revealed no signif- icant group × condition interaction effects for the excursions of pelvic anterior rotation (P =0 63), pelvic drop (P =0 95), 3.2. Isokinetic Variables. For the passive hip torque, ANOVAs demonstrated significant effects for group × condition inter- hip adduction (P =0 85), and hip internal rotation (P =0 48) during walking (Table 2). Therefore, the interven- action (P =0 002) and no significant effect for group × tion and control groups did not show changes after the inter- condition × varus alignment interaction (P =0 98) (Table 4). vention period. The contrasts revealed that the intervention group increased However, a significant effect for the interaction group × the passive torque (P =0 001) after muscle strengthening, condition × varus alignment was demonstrated for pelvic and the control group did not change after eight weeks drop (P =0 01). The contrasts showed that the subgroup of (P =0 25) (Table 5). Therefore, the intervention group smaller varus alignment reduced pelvic drop after strength- showed a change while the control group did not, and these ening (P =0 03) (Table 3). For the subgroup of larger FAC results were not dependent on the varus alignment. 8 Applied Bionics and Biomechanics Table 3: Mean, SD, and significance for the pelvic drop excursions of the varus alignment subgroups, in the intervention and control groups, before and after strengthening. Pelvic drop excursion ( ) Effect size Subgroups Condition Pt Power Mean (SD) Cohen’s d Preinterv. 5.62 (2.11) 0.03 SVI 2.42 0.68 0.38 Postinterv. 5.06 (2.18) Preinterv. 6.24 (2.45) LVI 0.06 -2.11 0.58 0.49 Postinterv. 6.80 (2.17) Preinterv. 4.95 (1.42) SVC 0.70 -0.39 0.10 0.07 Postinterv. 5.04 (1.42) Preinterv. 3.25 (2.03) LVC 0.81 0.25 0.07 0.06 Postinterv. 3.20 (2.16) SD: standard deviation; t: t value for the t-test (contrast); interv.: intervention; ( ): degrees; LVI: larger varus intervention; SVI: smaller varus intervention; LVC: larger varus control; SVC: smaller varus control. P ≤ 0 05 in the comparison between the pre- and postintervention conditions of the varus alignment subgroups, in the control and intervention groups. 4. Discussion Table 4: Significance of the interactions of interest for the passive and active torques. Hip and trunk muscular strengthening significantly reduced Group × condition the excursions of pelvic drop during walking, exclusively in Group × condition Variables × varus alignment the subgroup of individuals with smaller values of FAC varus PF P F alignment. There was also an increase in pelvic drop, with a 0.002 Hip passive torque 10.96 0.98 0.001 tendency towards statistical significance, in the subgroup with larger FAC varus alignment. When considering all indi- <0.001 Concentric torque peak 28.01 0.21 1.64 ∗ viduals (without subgrouping by varus alignment), no kine- <0.001 Eccentric torque peak 41.27 0.10 2.82 matic changes were found in the intervention group or in P ≤ 0 05; F: F value for the interaction in mixed ANOVA. the control group, after the intervention period. Muscular strengthening increased hip active torques (concentric and eccentric) and hip passive torque, independently of FAC ANOVAs showed significant group × condition interac- alignment. Consistent with previous studies [14, 15], the tions for the concentric (P <0 001) and eccentric (P <0 001) assumption that women with larger FAC varus alignment peak torques of the hip external rotators (Table 4). However, would have greater excursions of FAC pronation was no significant effect was found for the interaction group × confirmed for the forefoot-shank eversion excursion. The condition × varus alignment (concentric torque P =0 21 present findings showed that the effect of the muscle and eccentric torque P =0 10) (Table 4). The contrasts strengthening program on pelvic drop depended on the mag- revealed that the intervention group increased the concen- nitude of the FAC varus alignment. The following were tric peak torque (P <0 001) and the eccentric peak torque observed: (a) reduction in pelvic drop only in the subgroup (P <0 001) after the strengthening program (Table 5). No of women with smaller varus alignment and (b) a tendency change in concentric (P =0 62) and eccentric (P =0 22) tor- for pelvic drop increase in the subgroup of women with ques was observed in the control group after eight weeks larger varus alignment. (Table 5). Thus, the intervention group showed changes Previous studies that investigated consequences of hip while the control group did not, and these results were not strengthening on the kinematics of the pelvis [11] and hip dependent on the varus alignment. kinetics [12] during walking found no effects. Kendall et al. [11] identified that strength increases of hip abductors did 3.3. Foot-Ankle Complex (FAC) Kinematics. The Mann- not reduce the pelvic drop during walking, in patients with Whitney test revealed that, in the preintervention condition, nonspecific low back pain. This finding coincides with the participants with smaller varus alignment had lower excur- results of the present study, when all participants were con- sions of forefoot-shank eversion (9 86 ± 4 09) compared to sidered together (Table 2). This is a possible consistency across findings, although there are important methodological the participants with larger varus alignment (14 88 ± 4 17) (P <0 001). Moreover, the independent t-test showed no and sample differences among the studies. In contrast to the significant difference in rearfoot-shank eversion during observed absence of kinematic effects of strengthening, the stance phase of walking between the groups with larger present study found significant effects on pelvic kinematics, and smaller varuses in the preintervention condition when FAC varus alignment was considered. Increases in torque did not differ between individuals (9 18 ± 2 78 and 7 80 ± 3 25, respectively) (P =0 10). There- fore, the participants with smaller varus alignment showed with larger and smaller varus alignments. Thus, the pelvic lower forefoot-shank eversion than the participants with drop reduction observed only in the subgroup of individuals larger varus alignment. with smaller FAC varus alignment does not seem to be Applied Bionics and Biomechanics 9 Table 5: Mean, SD, and significance of mean hip passive torque and concentric and eccentric peak torques before and after strengthening, in the intervention and control groups. Passive mean Concentric peak Eccentric peak Groups Condition torque (Nm) Pt torque (Nm) Pt torque (Nm) Pt Mean (SD) Mean (SD) Mean (SD) Preinterv. 1.28 (0.59) 25.16 (5.03) 29.38 (6.23) ∗ ∗ ∗ 0.001 <0.001 <0.001 Intervention -3.97 -6.54 -7.67 Postinterv. 1.60 (0.67) 34.56 (8.32) 40.11 (9.24) Preinterv. 1.28 (0.58) 27.29 (7.20) 30.28 (6.88) Control 0.25 1.19 0.62 -0.50 0.22 -1.27 Postinterv. 1.15 (0.63) 27.77 (5.54) 31.18 (6.30) SD: standard deviation; Nm: Newton meter; interv.: intervention; t: t value for the t-test (contrast). P ≤ 0 05. related with particular increases of active and passive hip tor- interventions would allow the motor system to explore the ques in this subgroup. Thus, other factors may also contrib- new resources provided by strengthening (i.e., greater passive ute to the control of the pelvis motion in the frontal plane. torque and capability of producing greater active torques). It has been reported that individuals with larger varus align- Functional training in addition to muscle strengthening ment show greater FAC pronation [14, 15] and tend to have might be more effective in changing excursions of pelvic greater hip adduction and pelvic drop [19]. The relation anterior rotation and hip internal rotation and adduction between increased FAC varus alignment and increased fore- [2, 3, 37–39]. In addition, strengthening programs with foot eversion during walking was confirmed in the present greater training volume (i.e., capable of generating greater study. Therefore, the present results suggest that torque modifications in the musculoskeletal tissue and muscular increases after strengthening interacted with the presence of properties) could be necessary to produce kinematic effects smaller FAC varus alignment to reduce pelvic drop. These on the pelvis in the transverse plane and the hip in the frontal findings suggest that the strengthening program is recom- and transverse planes. Although the increase in maximum mended to reduce pelvic drop in individuals with smaller active torque produced during an isokinetic test does not FAC varus alignment. necessarily mean that an active torque increase will occur The subgroup with larger FAC varus alignment had a during walking [40], the increase in passive joint torque mea- sured isokinetically will contribute to the motions in walking. tendency to increase pelvic drop after strengthening, with a marginal significance (P =0 06). As the effect size was mod- Hence, greater increases in passive torque could result in erate and the achieved statistical power was low (less than greater kinematic changes after strengthening. However, it 80%) (Table 3), it is possible that a larger sample could reach is important to note that the strengthening program used in statistical significance. In addition, this subgroup demon- this study can be considered to have a medium-to-high vol- ume training [32]. strated a high variability in pelvic drop changes, which may have also reduced the study’s statistical power (Table 3). This It should be noted that the average 0.56 reduction in possible increase in pelvic drop may be due to hip and trunk pelvic drop observed in the smaller varus subgroup could adaptations to factors not measured in this study, which be viewed as a small change with limited clinical relevance. could have happened in response to the stimuli provided by However, this change represents approximately 13% of the the muscle strength training. For example, hip abductor pas- average total pelvic drop excursion observed. Pelvic and hip sive torque may be reduced when the muscles are used in kinematic changes of similar magnitudes may be relevant. greater lengths during daily activities [36]. People with For example, runners with patellofemoral pain have 11% increased foot pronation, such as those with larger varus more hip adduction compared to healthy controls [41]. Gait alignment, have greater hip adduction [19, 20]. This along retraining reduced pelvic drop in 24% and reduced pain in with the muscle training might have led to adaptations in runners with patellofemoral pain [42]. Since hip adduction the abductor muscles. However, this is very speculative and is related to closed-chain pelvic drop [9], the reduction in would need further investigation. Therefore, further studies pelvic drop found in the present study might contribute to are needed to better investigate the effects of hip and trunk clinical improvements. In addition, a similar rationale strengthening in people with larger varus alignment. At this can be applied for the increase in pelvic drop observed point, caution is advised in the use of the studied muscle in the larger varus subgroup (average increase of 0.56 ). strengthening program for individuals with larger FAC varus It is also possible that this small change could be poten- alignment, considering the possible increase in pelvic drop. tially harmful [5, 6]. However, this needs to be subjected The increases in hip (external rotator) passive torque and to further investigation. active concentric and eccentric torques in the intervention Some limitations of the present study can be pointed out. group did not influence hip excursion in the frontal and First, there is a technical difficulty to adequately capture thigh transverse planes and pelvis excursion in the transverse kinematics, especially in the transverse plane, due to large plane. Perhaps, the implementation of neuromuscular train- errors related to soft tissue artifacts [25, 43]. In addition to ing during walking and/or the use of weight-bearing exercises its contribution to greater data variability, this difficulty performed in conditions more similar to the stance phase of may have prevented the detection of strengthening effects walking could produce more consistent results. These in hip kinematics. Unfortunately, this is a limitation of the 10 Applied Bionics and Biomechanics noninvasive motion-tracking procedure that is currently rec- Supplementary Materials ommended for hip kinematic assessment [43]. Another lim- Figure S1: measurement of foot-ankle complex varus align- itation was the nonrandom allocation of the participants in ment (forefoot-shank angle): (a) posterior view and (b) groups. Participants were allocated to groups according to lateral view [15]. Table S1: descriptive data (mean and stan- their availability to participate in the program (convenience dard deviation) of the kinematic and isokinetic variables method), which was necessary to make the study data collec- before and after the intervention for the intervention and tion feasible. Finally, only able-bodied and asymptomatic control groups and for the subgroups related to the foot- women participated in the study, which limits results’ gener- ankle complex varus alignment. (Supplementary Materials) alization. However, the study results may apply to programs that are aimed at preventing orthopedic problems in the lum- References bopelvic complex, in this population. Future studies could evaluate the effect of hip and trunk muscle strengthening in [1] K. R. Snyder, J. E. Earl, K. M. O’Connor, and K. T. 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In addition, there was a tendency for ics award winner 2006,” Clinical Biomechanics, vol. 22, no. 9, pelvic drop increases in women who have larger FAC varus pp. 951–956, 2007. alignment. The strengthening increased passive and active [6] R. A. Zifchock, I. Davis, J. Higginson, S. McCaw, and T. Royer, hip torques in the transverse plane, regardless of the magni- “Side-to-side differences in overuse running injury susceptibil- tude of FAC varus alignment. These results indicate that ity: a retrospective study,” Human Movement Science, vol. 27, specific individual characteristics, such as FAC alignment, no. 6, pp. 888–902, 2008. may influence the kinematic effects of proximal muscle [7] Y. P. Huang, S. M. Bruijn, J. H. Lin et al., “Gait adaptations in strengthening. 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Copyright © 2019 Aline de Castro Cruz et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Abstract

Hindawi Applied Bionics and Biomechanics Volume 2019, Article ID 2018059, 12 pages https://doi.org/10.1155/2019/2018059 Research Article Pelvic Drop Changes due to Proximal Muscle Strengthening Depend on Foot-Ankle Varus Alignment 1 1,2 1,2 Aline de Castro Cruz , Sérgio Teixeira Fonseca , Vanessa Lara Araújo , 1 1 1 Diego da Silva Carvalho, Leonardo Drumond Barsante, Valéria Andrade Pinto , 1,2 and Thales Rezende Souza Graduate Program in Rehabilitation Sciences, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil Department of Physical Therapy, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil Correspondence should be addressed to Thales Rezende Souza; thalesrs@ufmg.br Received 30 November 2018; Revised 11 March 2019; Accepted 21 March 2019; Published 12 May 2019 Academic Editor: Craig P. McGowan Copyright © 2019 Aline de Castro Cruz et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Strengthening of hip and trunk muscles can modify pelvis and hip movements. However, the varus alignment of the foot-ankle complex (FAC) may influence the effects of muscle strengthening, due to the relationship of FAC alignment with pelvic and hip kinematics. This study evaluated the effects of hip and trunk muscle strengthening on pelvis and hip kinematics during walking, in subgroups with larger and smaller values of FAC varus alignment. In addition, this study evaluated the effects of hip and trunk muscle strengthening on hip passive and active properties, in the same subgroups. Methods. Fifty-three women, who were divided into intervention and control groups, participated in this nonrandomized controlled trial. Each group was split into two subgroups with larger and smaller values of FAC varus alignment. Hip and trunk muscle strengthening was performed three times a week for two months, with a load of 70% to 80% of one repetition maximum. Before and after strengthening, we evaluated (1) pelvis and hip excursions in the frontal and transverse planes during walking, (2) isokinetic hip passive external rotator torque, and (3) isokinetic concentric and eccentric peak torques of the hip external rotator muscles. Mixed analyses of variance (ANOVAs) were carried out for each dependent variable related to walking kinematics and isokinetic measurements (α =0 05). Results. The subgroup with smaller varus alignment, of the intervention group, presented a reduction in pelvic drop after strengthening (P =0 03). The subgroup with larger varus alignment increased pelvic drop after strengthening, with a marginal significance (P =0 06). The other kinematic excursions did not change (pelvic anterior rotation P =0 30, hip internal rotation P =0 54, and hip adduction P =0 43). The intervention group showed increases in passive torque (P =0 002), peak concentric torque (P <0 001), and peak eccentric torque (P <0 001), independently of FAC alignment. These results suggest that FAC varus alignment influences the effects of strengthening and should be considered when hip and trunk muscle strengthening is used to reduce pelvic drop during walking. 1. Introduction hip external rotators and abductors may increase passive and active (eccentric) mechanical resistance against hip Strengthening of hip and trunk muscles has been used to internal rotation and adduction [3, 4, 10]. In addition, modify pelvis and hip excessive movements [1–4] since they strengthening of trunk rotators and lateral flexors may may be involved in the production of injuries of the hip [5, increase passive and eccentric resistance against pelvic drop 6] and the lumbopelvic complex [7]. Pelvic drop, axial rota- and axial rotation [3, 4, 8, 9]. Gains in concentric strength of these muscles could also facilitate the production of hip tion, hip adduction, and hip internal rotation occur in the first half of the stance phase of walking [8, 9]. Muscle external rotation and abduction, as well as pelvic raise. These strengthening may be used in an attempt to reduce ampli- movements take place subsequently in the second half of the tude of these motions. For example, strengthening of the stance phase [9]. Despite these theoretical benefits, previous 2 Applied Bionics and Biomechanics 25 kg/m studies have demonstrated no effects of hip strengthening on to facilitate palpation of anatomical landmarks for the kinematics [11] and kinetics [12] of the pelvis and hip the kinematic model creation; (4) absence of self-reported during walking. musculoskeletal symptoms or injuries in the last three Biomechanical characteristics other than the active and months, to prevent the impact of pain and previous injury passive functions of the hip and trunk muscles could influ- on the assessed movement pattern; (5) no practice of physical ence lower limb kinematics in weight-bearing tasks [10, 13] exercise in the last three months, to remove possible con- and affect the kinematic changes produced by the strength- founding effects of other physical exercises on the strength- ening. Varus alignment of the foot-ankle complex (FAC), ening protocol used in this study; and (6) presence of measured in non-weight-bearing, constitutes a biomechani- normal range of motion of hip internal rotation (from 34 ° ° ° cal factor that influences the magnitude of FAC pronation to 71 ) and hip external rotation (from 25 to 56 ) [22]. Peo- during walking [14, 15]. By its turn, the magnitude of FAC ple with hip internal and external rotation restrictions could pronation during weight-bearing tasks may influence hip have difficulties to perform the strengthening exercises prop- and pelvis kinematics [16–20]. Higher FAC pronation values erly. In addition, these individuals might also have anatomi- are related to higher magnitudes of hip internal rotation and cal abnormalities such as anteversion or retroversion of the adduction [17–20] and pelvic drop [16, 19]. Therefore, the femoral neck, which could influence changes in hip kinemat- magnitude of FAC varus alignment (and the magnitude of ics after muscular strengthening. The exclusion criteria were FAC pronation) may be an individual biomechanical charac- (1) adherence lower than 80% of the training sessions of the teristic that influences the effects of muscle strengthening on strengthening program. The time needed for hypertrophy changing pelvis and hip motions. For example, larger values gains in the lower limbs of women is about six weeks, after of FAC varus alignment may result in greater FAC pronation the beginning of training, which corresponds to 80% of the [14, 15] and produce greater hip adduction and pelvic drop duration of the training protocol used in our study [23]; (2) [16–20] during walking. Thus, the presence of larger varus engagement in physical exercise during the study period, could make it difficult to produce an amplitude reduction to prevent possible confounding effects of other physical of these motions, after proximal muscle strengthening. exercises on the strengthening protocol used in this study The objective of this study was to investigate the influ- (physical exercise was considered as the practice of activities ence of FAC varus alignment on possible changes resulting or training aiming to improve physical fitness or health); (3) from muscle strengthening at the hip (mainly abductors inability to keep the hip muscles relaxed during the passive and lateral rotators) and trunk (mainly abdominals and latis- torque test; and (4) presence of pain during the assessments simus dorsi). We considered possible changes in (1) the and inability to perform the tests correctly. motion excursions of the pelvis and hip in the frontal and FAC varus alignment measurements were performed in transverse planes, during gait, and (2) hip muscle strength both lower limbs of the participant. Allocation in the control and passive torque. The main study hypotheses were that a and intervention groups was performed according to the subgroup with larger FAC varus alignment would have availability of participants to perform the intervention. For smaller or no reductions in the excursions of pelvis and hip allocation in the larger and smaller FAC subgroups, the motions. Changes in hip strength and passive torque were control and intervention groups were divided in relation to also investigated to help understand possible kinematic varus values by means of the 50th percentile. However, in effects. A secondary study objective was to verify if individ- order to guarantee that the varus alignment values were sim- uals with larger FAC varus alignment have larger foot prona- ilar between the control and intervention groups, it was tion during walking, as previously observed [14, 15]. necessary to match the groups according to varus values. Thus, the participants from the intervention group were eval- uated, and the definition of which limb should be analyzed 2. Methods was random (drawing). For the control group, the varus 2.1. Participants. Fifty-three women, who were divided into alignment was evaluated in both limbs, and the limb analyzed intervention and control groups, participated in this nonran- was selected to match the varus value of a participant from domized controlled trial. Both groups were divided into the intervention group. This matching procedure was done to guarantee that the subgroups from the intervention and subgroups of larger and smaller varus magnitudes. The par- ticipants were selected by means of convenience sampling. control groups were similar according to the magnitude of The number of participants was calculated based on an FAC varus. expected moderate effect size (f =0 3), with a level of signifi- Initially, fifty-six women were included in the study. The cance of 0.05 and a desired statistical power of 0.80. Accord- participants signed an informed consent form to participate in the study. The intervention group (n =26) was divided ing to this analysis, approximately 58 individuals would be needed. This study was approved by the institution’s into two subgroups: one with smaller varus alignment Research Ethics Committee (CAAE–0427.0.203.000-11). (n =13) and another with larger varus alignment (n =13). The control group (n =27) was also split into subgroups with The inclusion criteria were (1) female, since women pres- ent greater pelvic drop and hip adduction compared to men smaller varus alignment (n =14) and larger varus alignment (n =13) (Figure 1). The groups were divided according to [19, 20] and may be more frequently subjected to interven- tions intended to reduce pelvic and hip motions; (2) age the median varus alignment values to equally separate them between 18 and 35 years, to avoid the impact of age on hyper- into subgroups of larger and smaller varus alignments. In trophy [21]; (3) body mass index (BMI) less than or equal to addition, this division also allowed to investigate whether Applied Bionics and Biomechanics 3 Assessed for inclusion criteria (n = 111) Not meeting inclusion criteria (n = 55) Participated in the study (n = 56) Intervention group (n = 28) Control group (n = 28) SVI (n = 14) e LVI (n = 14) SVC (n = 14) e LVC (n = 14) Excluded for not performing at least 80% of Excluded for having started the practice of training (n = 1) physical exercise (n = 1) Control group (n = 27) Intervention group (n = 27) SVI (n = 14) e LVI (n = 13) SVC (n = 14) e LVC (n = 13) Variables: Variables: - Kinematics and hip active torque - Kinematics and hip active torque Intervention group (n = 26) Control group (n = 27) SVI (n = 13) e LVI (n = 13) SVC (n = 14) e LVC (n = 13) Excluded due to technical problems in kinematic data (n = 1). - Hip passive torque - Hip passive torque Intervention group (n = 25) Control group (n = 26) SVI (n = 13) e LVI (n = 12) SVC (n = 13) e LVC (n = 13) Excluded due to atypical pattern of the passive Excluded due to atypical pattern of the passive torque curve (n = 1) and due to technical torque curve (n = 1) problems in kinematic data (n = 1) Figure 1: Flow diagram showing the number of participants at each stage of the study. LVI: larger varus in the intervention group; SVI: smaller varus in the intervention group; LVC: larger varus in the control group; SVC: smaller varus in the control group. the varus values of the subgroups are associated with FAC values of the forefoot-shank angle as larger values of FAC pronation amplitude during gait. varus alignment. The mean of three forefoot-shank angle Independent t-tests showed that FAC alignment values measures was calculated and used for analysis. The were significantly different between the subgroups of the intraexaminer reliability of this measure was evaluated intervention group (P <0 001) and between the subgroups with ten individuals who performed two evaluations with a of the control group (P <0 001). The smaller varus sub- one-week interval, and the intraclass correlation coefficient groups, in the control and intervention groups, did not show (ICC) obtained was 0.93. significant differences in varus alignment (P =0 57). The larger varus subgroups, in the control and intervention 2.3. Evaluation of Walking Kinematics. A three-dimensional groups, did not show significant differences in varus align- motion analysis system Codamotion (Charnwood Dynamics, ment neither (P =0 71). The characteristics of the subgroups Rothley, England) was used. Motion of the pelvis, thigh, are indicated in Table 1. shank, rearfoot, and forefoot was captured with clusters of active tracking markers that were placed on each of these 2.2. Evaluation of Foot-Ankle Complex (FAC) Alignment: body segments [4]. Moreover, anatomical markers (two Forefoot-Shank Angle. The FAC alignment was assessed by proximal and two distal markers) were used in each segment means of a clinical measure that combines the varus/valgus for the kinematic model definition [4, 25]. Initially, the par- alignment of the FAC (forefoot, rearfoot, and shank align- ticipant remained in orthostatic position for a static data col- lection of five seconds. The position of the participant’s feet ments) and midfoot inversion mobility [15, 24]. This clinical measure provides the forefoot-shank angle, measured in was drawn on a paper to be reproduced during reassessment. open chain (see Figure S1 in Supplementary Materials). In This static posture data with both tracking and anatomical the present study, for simplification, we considered larger markers was later used to create the kinematic model. After Monitoring of Allocation of Recruitment of Analysis participants participants participants 4 Applied Bionics and Biomechanics Table 1: Characteristics of the subgroups. Age (years) BMI (kg/m ) FAC varus ( ) Groups Subgroups Evaluated limb Mean (SD) Mean (SD) Mean (SD) Left (n =7) Smaller varus 21 (2.95) 20.80 (1.57) 9.51 (4.44) Right (n =6) Intervention Left (n =7) Larger varus 23 (3.88) 21.39 (2.24) 22.08 (4.68) Right (n =6) Left (n =2) Smaller varus 22 (1.73) 20.63 (2.10) 10.54 (4.75) Right (n =12) Control Left (n =7) Larger varus 21 (1.97) 21.31 (2.10) 21.45 (3.79) Right (n =6) SD: standard deviation; BMI: body mass index; FAC: foot-ankle complex. analyzed trials was due to an uneven number of marker losses the static data collection, the participant walked on an electric treadmill (ProAction G635 Explorer, BH Fitness; among the subjects. However, none of the subjects had less Vitoria-Gasteiz, Alava, Spain) with the tracking markers than 10 trials included in the analysis [29]. only. Thirty consecutive walking cycles were collected at a Motion excursions during the stance phase of walking sampling rate of 100 Hz. The participant was asked to walk were calculated for pelvic anterior rotation (transverse plane), at her self-selected comfortable speed, in the first evaluation. pelvic drop (frontal plane), hip internal rotation (transverse The same speed was used in the reevaluation (i.e., after the plane), and hip adduction (frontal plane). Motion excursion intervention period). The mean and range of speed of the was computed as the difference between the angle obtained subgroups were as follows: smaller varus intervention group in the first frame of stance (i.e., at initial contact) and the peak (3.08 km/h (SD 0.73), 2.00 to 4.00), larger varus intervention angle within the stance phase. For statistical analyses, the group (3.15 km/h (SD 0.59), 2.00 to 4.00), smaller varus con- outcome variables were the average excursions obtained from trol group (3.07 km/h (SD 0.55), 2.00 to 3.50), and larger the included trials of each participant. Rearfoot-shank and varus control group (2.73 km/h (SD 0.52), 2.00 to 3.50). An forefoot-shank eversion excursions (frontal plane) were cal- initial statistical analysis was done to verify if the velocities culated only for the prestrengthening evaluation, since these were different among the subgroups. A two-way ANOVA variables were used only to verify if individuals with larger was performed with the factors group (control and interven- varus alignment show greater FAC pronation during walking. tion) and varus alignment (smaller and larger). Since the The test-retest reliability of all outcome variables (i.e., velocity was exactly the same in the evaluation and reevalua- excursions of the pelvis, hip, rearfoot-shank, and forefoot- tion, the condition was not a factor for this analysis. The shank motions) was evaluated in a pilot study with ten par- interaction group × varus alignment revealed that the veloc- ticipants in two evaluations with a one-week interval. This ity was not different among the subgroups (P =0 analysis showed moderate to good reliability (intraclass cor- 214). Visual 3D software (C-Motion Inc., Rockville, Maryland, relation coefficients ranging from 0.77 to 0.89). USA) was used to process the kinematic data. The data were 2.4. Isokinetic Evaluation: Passive Torque and Hip Muscle filtered with a fourth-order, Butterworth, zero-lag, low-pass filter, with a cut-off frequency of 6 Hz. From the static Strength. Hip passive torque and muscle strength were mea- posture data, a rigid body kinematic model of six degrees of sured with an isokinetic dynamometer Biodex 3 Pro (Bio- freedom was created [25–27] and applied to the walking trial. dex Medical Systems, Shirley, USA) at a sampling rate of The pelvis angle (pelvic motion in relation to the global coor- 100 Hz. During passive hip measurement, the dynamometer was in the passive mode, and a surface electromyography dinate system) and hip angle (thigh motion in relation to the pelvis) were calculated in the frontal and transverse planes system (ME6000, Mega Electronics Inc., Kuopio, Finland) during the stance of walking. Furthermore, rearfoot-shank was used to ensure that hip muscles were relaxed. Electro- and forefoot-shank angles (rearfoot and forefoot motions myographic data were collected at a sampling rate of in relation to the shank) were calculated in the frontal 1000 Hz and recorded using the MegaWin 3.0 software (Mega Electronics Inc., Kuopio, Finland). Active surface elec- plane during the stance of walking. These angles were cre- ated with the following Cardan sequence: lateral-medial, trodes were placed on the following muscles: gluteus maxi- anterior-posterior, and superior-inferior [25]. mus, gluteus medius, biceps femoris, tensor fascia lata, and The stance phase of walking was defined as the period adductor magnus [30]. from the instant the calcaneus contacted the ground until For the measurement of the hip passive torque during internal rotation, the participant was positioned in prone, the instant the toes left the ground. These events were estab- lished by two examiners who concurrently observed the ante- with the knee flexed at 90 and the tibial tuberosity aligned roposterior displacement curves of rearfoot and forefoot with the axis of rotation of the isokinetic dynamometer. tracking markers [28]. Ten to sixteen walking stance phases The upper limbs of the participant were placed next to the without any marker tracking loss were analyzed for each trunk, and a belt was used to stabilize the pelvis. The equip- participant. This intersubject variation in the number of ment’s attachment moved the participant’s hip from 25 of Applied Bionics and Biomechanics 5 and the poststrengthening evaluation was two months, with a external rotation to 25 of internal rotation, at an angular velocity of 5 /s [4]. The examiner instructed the participant maximum limit of two months and one week. The training to remain relaxed and not to resist and/or assist hip motion days were chosen according to the participant’s availability. during the test. Before the test, five repetitions of the move- The load for the exercises was set at 70% to 80% of one ment were made for tissue viscoelastic accommodation and repetition maximum (1RM) [32], as this load level is rec- participant familiarization. Moreover, electromyographic ommended when hypertrophy is aimed [32]. During the signals of the muscles were recorded with the participant 1RM test, the examiner observed the movement to ensure resting in static position. During the test, three valid mea- that the participant performed the exercise throughout the sures of hip passive torque were performed. At each repeti- full range of motion without compensatory movements tion of the test, the electromyographic data were extracted (i.e., movement components performed by muscles other and processed in MATLAB software (The MathWorks than the muscles being tested). For each exercise of the Inc.). The data was filtered using a fourth-order, Butterworth, protocol, three sets of eight to nine repetitions were per- bandpass filter, with cut-off frequencies of 10 and 500 Hz. formed at moderate velocity (about 3 seconds for the iso- The signal collected during the participant’s rest was com- tonic cycle) with a one-minute rest between sets [32]. pared to the signal obtained during each test. The repetitions The load was increased by 5 or 10% when the participant with muscular activity were defined as those in which the was able to perform three sets of nine repetitions for two con- electromyography signal was equal to or greater than the secutive sessions [32]. In the fifth week, the eccentric training mean plus two standard deviations of the signal captured at of hip external rotators and abductors was increased to 90% rest. When muscle contraction occurred, a new repetition or 100% of 1 concentric RM [33, 34]. Bilateral isotonic of the test was performed. strengthening was performed in full range of motion for the The evaluation of the active maximum concentric and following muscles: (a) hip external rotators, (b) gluteus med- eccentric hip external rotation torques was performed with ius, (c) latissimus dorsi, (d) oblique and rectus abdominis the participant in the same position of the passive torque test, and quadratus lumborum, and (e) hip and trunk rotators except for the upper limbs. The participant was instructed to and extensors in closed kinematic chain [4]. It was expected hold a belt placed under the chair and keep the shoulders and that the strengthening of these muscles could reduce exces- elbows flexed to stabilize the trunk during the test. For famil- sive motion excursions of the pelvis and hip in the frontal iarization, before the test, the participant performed the and transverse planes. Hip external rotators and abductor movement with submaximal force for five repetitions. The muscles could resist hip excessive internal rotation and ° ° tests were performed from 30 of internal rotation to 20 of adduction [8, 9]. The trunk muscles also have the potential external rotation at an angular velocity of 30 /s [4]. During to resist hip adduction and internal rotation [8, 9]. Tension external rotation, the hip muscles contracted concentrically. in the latissimus dorsi muscle can be transmitted to the During internal rotation, the muscles contracted eccentri- gluteus maximus through the thoracolumbar fascia and cally. The participant received instructions and verbal increases hip resistance against internal rotation [35]. The encouragement to produce maximum strength. Three sets oblique abdominal muscles can reduce ipsilateral pelvic drop of five repetitions were performed, and the concentric and and contralateral hip adduction [8, 9]. Therefore, the open- eccentric torques of each repetition were recorded. chain exercises depicted in Figure 2 were chosen to selectively For data reduction, the participant’s shank and foot strengthen the desired muscles. lengths were measured. In addition, a repetition of the test The last exercise (Figure 2(e)) was initiated only in the third week with minimal load (5 kg), aiming to learn the without the participant was performed to record the torque produced by the weight of the equipment’s lever arm. correct execution of the movement. In the fifth week, the load The data obtained by the isokinetic dynamometer were of this exercise was increased to 70% or 80% of 1RM [4]. The processed with a routine developed in MATLAB. The signals purpose of this exercise was to promote a more global were filtered with a fourth-order, Butterworth, low-pass fil- strengthening, for the muscles that can help extend and rotate the hip and trunk. It was performed in a weight-bearing situ- ter, with a cut-off frequency of 1.25 Hz. The torques gener- ated by the shank, foot, and dynamometer’s lever arm ation such as the stance phase of walking. Although this last weights were subtracted from the total torque [4]. exercise was performed in weight bearing, one objective of For the passive torque, the mean torque produced during the present study was to investigate the kinematic effects of the first 20 of hip internal rotation was calculated, in Newton changes in the active and passive functions of the muscles regardless of the exercises being performed in open- or meters (Nm), for each test repetition [4]. This amplitude of hip internal rotation was chosen as an approximation of the closed-chain situations. average range of hip rotation during walking [31]. For the active torques, the peak values of the concentric and eccentric 2.6. Statistical Analysis. Mixed analyses of variance (ANO- torques were calculated for each repetition. For statistical VAs) were carried out for each dependent variable: excursion of pelvic anterior rotation, pelvic drop excursion, hip internal analysis, the mean of the three repetitions was used, for the passive, concentric, and eccentric torques. rotation excursion, and hip adduction excursion; passive hip torque; and concentric and eccentric hip external rotator tor- 2.5. Muscle Strengthening Protocol. Hip and trunk muscle ques. Each ANOVA had two between-subject effects with strengthening was performed three times a week for two two levels (varus alignment: larger and smaller; group: con- trol and intervention) and one within-subject effect with months. The period between the prestrengthening evaluation 6 Applied Bionics and Biomechanics (a) (b) (c) (d) Figure 2: Continued. Applied Bionics and Biomechanics 7 (e) Figure 2: Strengthening exercises of the hip and trunk muscles: (a) hip external rotators, (b) gluteus medius, (c) latissimus dorsi, (d) abdominal oblique and quadratus lumborum, and (e) hip and trunk rotators and extensors in closed kinematic chain. Source: [4]. Table 2: Significance of the kinematic variables for the interactions two levels (condition: pre- and postintervention). Each of interest. mixed ANOVA performed for each dependent variable Group × condition × generated the following interactions of interest: group × Group × condition Variables varus alignment condition and group × condition × varus alignment. When a PF P F significant difference was found in the interaction effect, pre- planned contrasts were used to identify which group and Pelvis frontal 0.95 0.004 0.01 7.12 subgroup comparisons showed significant differences. Pelvis transverse 0.63 0.23 0.30 1.11 After verifying data normality by means of Shapiro- Hip frontal 0.85 0.03 0.43 0.63 Wilk tests, independent t-tests were performed to compare Hip transverse 0.48 0.50 0.54 0.38 the rearfoot-shank eversion angle (data with normal distri- P ≤ 0 05; F: F value for the interaction in mixed ANOVA. bution) between subgroups of smaller and larger varus alignments. Moreover, the Mann-Whitney test was carried out to compare the forefoot-shank eversion angle (data varus, a marginal P value (P =0 06) was observed, which with nonnormal distribution) between subgroups of smaller shows a tendency of increase in pelvic drop during walking and larger varus alignments. For all analyses, a type 1 error (Table 3). In addition, both control groups with smaller and probability of 5% (α =0 05) was considered. larger varus alignments did not show significant differences in pelvic drop after eight weeks (P =0 70 and P =0 81, 3. Results respectively). Thus, the intervention group showed a change after the intervention period, for pelvic drop, only when it Descriptive data of all outcome variables are presented in was divided into smaller and larger varus alignment sub- Supplementary Materials (see Table S1). groups. And the same subgroups in the control group did not show any changes. 3.1. Pelvis and Hip Kinematics. ANOVAs revealed no signif- icant group × condition interaction effects for the excursions of pelvic anterior rotation (P =0 63), pelvic drop (P =0 95), 3.2. Isokinetic Variables. For the passive hip torque, ANOVAs demonstrated significant effects for group × condition inter- hip adduction (P =0 85), and hip internal rotation (P =0 48) during walking (Table 2). Therefore, the interven- action (P =0 002) and no significant effect for group × tion and control groups did not show changes after the inter- condition × varus alignment interaction (P =0 98) (Table 4). vention period. The contrasts revealed that the intervention group increased However, a significant effect for the interaction group × the passive torque (P =0 001) after muscle strengthening, condition × varus alignment was demonstrated for pelvic and the control group did not change after eight weeks drop (P =0 01). The contrasts showed that the subgroup of (P =0 25) (Table 5). Therefore, the intervention group smaller varus alignment reduced pelvic drop after strength- showed a change while the control group did not, and these ening (P =0 03) (Table 3). For the subgroup of larger FAC results were not dependent on the varus alignment. 8 Applied Bionics and Biomechanics Table 3: Mean, SD, and significance for the pelvic drop excursions of the varus alignment subgroups, in the intervention and control groups, before and after strengthening. Pelvic drop excursion ( ) Effect size Subgroups Condition Pt Power Mean (SD) Cohen’s d Preinterv. 5.62 (2.11) 0.03 SVI 2.42 0.68 0.38 Postinterv. 5.06 (2.18) Preinterv. 6.24 (2.45) LVI 0.06 -2.11 0.58 0.49 Postinterv. 6.80 (2.17) Preinterv. 4.95 (1.42) SVC 0.70 -0.39 0.10 0.07 Postinterv. 5.04 (1.42) Preinterv. 3.25 (2.03) LVC 0.81 0.25 0.07 0.06 Postinterv. 3.20 (2.16) SD: standard deviation; t: t value for the t-test (contrast); interv.: intervention; ( ): degrees; LVI: larger varus intervention; SVI: smaller varus intervention; LVC: larger varus control; SVC: smaller varus control. P ≤ 0 05 in the comparison between the pre- and postintervention conditions of the varus alignment subgroups, in the control and intervention groups. 4. Discussion Table 4: Significance of the interactions of interest for the passive and active torques. Hip and trunk muscular strengthening significantly reduced Group × condition the excursions of pelvic drop during walking, exclusively in Group × condition Variables × varus alignment the subgroup of individuals with smaller values of FAC varus PF P F alignment. There was also an increase in pelvic drop, with a 0.002 Hip passive torque 10.96 0.98 0.001 tendency towards statistical significance, in the subgroup with larger FAC varus alignment. When considering all indi- <0.001 Concentric torque peak 28.01 0.21 1.64 ∗ viduals (without subgrouping by varus alignment), no kine- <0.001 Eccentric torque peak 41.27 0.10 2.82 matic changes were found in the intervention group or in P ≤ 0 05; F: F value for the interaction in mixed ANOVA. the control group, after the intervention period. Muscular strengthening increased hip active torques (concentric and eccentric) and hip passive torque, independently of FAC ANOVAs showed significant group × condition interac- alignment. Consistent with previous studies [14, 15], the tions for the concentric (P <0 001) and eccentric (P <0 001) assumption that women with larger FAC varus alignment peak torques of the hip external rotators (Table 4). However, would have greater excursions of FAC pronation was no significant effect was found for the interaction group × confirmed for the forefoot-shank eversion excursion. The condition × varus alignment (concentric torque P =0 21 present findings showed that the effect of the muscle and eccentric torque P =0 10) (Table 4). The contrasts strengthening program on pelvic drop depended on the mag- revealed that the intervention group increased the concen- nitude of the FAC varus alignment. The following were tric peak torque (P <0 001) and the eccentric peak torque observed: (a) reduction in pelvic drop only in the subgroup (P <0 001) after the strengthening program (Table 5). No of women with smaller varus alignment and (b) a tendency change in concentric (P =0 62) and eccentric (P =0 22) tor- for pelvic drop increase in the subgroup of women with ques was observed in the control group after eight weeks larger varus alignment. (Table 5). Thus, the intervention group showed changes Previous studies that investigated consequences of hip while the control group did not, and these results were not strengthening on the kinematics of the pelvis [11] and hip dependent on the varus alignment. kinetics [12] during walking found no effects. Kendall et al. [11] identified that strength increases of hip abductors did 3.3. Foot-Ankle Complex (FAC) Kinematics. The Mann- not reduce the pelvic drop during walking, in patients with Whitney test revealed that, in the preintervention condition, nonspecific low back pain. This finding coincides with the participants with smaller varus alignment had lower excur- results of the present study, when all participants were con- sions of forefoot-shank eversion (9 86 ± 4 09) compared to sidered together (Table 2). This is a possible consistency across findings, although there are important methodological the participants with larger varus alignment (14 88 ± 4 17) (P <0 001). Moreover, the independent t-test showed no and sample differences among the studies. In contrast to the significant difference in rearfoot-shank eversion during observed absence of kinematic effects of strengthening, the stance phase of walking between the groups with larger present study found significant effects on pelvic kinematics, and smaller varuses in the preintervention condition when FAC varus alignment was considered. Increases in torque did not differ between individuals (9 18 ± 2 78 and 7 80 ± 3 25, respectively) (P =0 10). There- fore, the participants with smaller varus alignment showed with larger and smaller varus alignments. Thus, the pelvic lower forefoot-shank eversion than the participants with drop reduction observed only in the subgroup of individuals larger varus alignment. with smaller FAC varus alignment does not seem to be Applied Bionics and Biomechanics 9 Table 5: Mean, SD, and significance of mean hip passive torque and concentric and eccentric peak torques before and after strengthening, in the intervention and control groups. Passive mean Concentric peak Eccentric peak Groups Condition torque (Nm) Pt torque (Nm) Pt torque (Nm) Pt Mean (SD) Mean (SD) Mean (SD) Preinterv. 1.28 (0.59) 25.16 (5.03) 29.38 (6.23) ∗ ∗ ∗ 0.001 <0.001 <0.001 Intervention -3.97 -6.54 -7.67 Postinterv. 1.60 (0.67) 34.56 (8.32) 40.11 (9.24) Preinterv. 1.28 (0.58) 27.29 (7.20) 30.28 (6.88) Control 0.25 1.19 0.62 -0.50 0.22 -1.27 Postinterv. 1.15 (0.63) 27.77 (5.54) 31.18 (6.30) SD: standard deviation; Nm: Newton meter; interv.: intervention; t: t value for the t-test (contrast). P ≤ 0 05. related with particular increases of active and passive hip tor- interventions would allow the motor system to explore the ques in this subgroup. Thus, other factors may also contrib- new resources provided by strengthening (i.e., greater passive ute to the control of the pelvis motion in the frontal plane. torque and capability of producing greater active torques). It has been reported that individuals with larger varus align- Functional training in addition to muscle strengthening ment show greater FAC pronation [14, 15] and tend to have might be more effective in changing excursions of pelvic greater hip adduction and pelvic drop [19]. The relation anterior rotation and hip internal rotation and adduction between increased FAC varus alignment and increased fore- [2, 3, 37–39]. In addition, strengthening programs with foot eversion during walking was confirmed in the present greater training volume (i.e., capable of generating greater study. Therefore, the present results suggest that torque modifications in the musculoskeletal tissue and muscular increases after strengthening interacted with the presence of properties) could be necessary to produce kinematic effects smaller FAC varus alignment to reduce pelvic drop. These on the pelvis in the transverse plane and the hip in the frontal findings suggest that the strengthening program is recom- and transverse planes. Although the increase in maximum mended to reduce pelvic drop in individuals with smaller active torque produced during an isokinetic test does not FAC varus alignment. necessarily mean that an active torque increase will occur The subgroup with larger FAC varus alignment had a during walking [40], the increase in passive joint torque mea- sured isokinetically will contribute to the motions in walking. tendency to increase pelvic drop after strengthening, with a marginal significance (P =0 06). As the effect size was mod- Hence, greater increases in passive torque could result in erate and the achieved statistical power was low (less than greater kinematic changes after strengthening. However, it 80%) (Table 3), it is possible that a larger sample could reach is important to note that the strengthening program used in statistical significance. In addition, this subgroup demon- this study can be considered to have a medium-to-high vol- ume training [32]. strated a high variability in pelvic drop changes, which may have also reduced the study’s statistical power (Table 3). This It should be noted that the average 0.56 reduction in possible increase in pelvic drop may be due to hip and trunk pelvic drop observed in the smaller varus subgroup could adaptations to factors not measured in this study, which be viewed as a small change with limited clinical relevance. could have happened in response to the stimuli provided by However, this change represents approximately 13% of the the muscle strength training. For example, hip abductor pas- average total pelvic drop excursion observed. Pelvic and hip sive torque may be reduced when the muscles are used in kinematic changes of similar magnitudes may be relevant. greater lengths during daily activities [36]. People with For example, runners with patellofemoral pain have 11% increased foot pronation, such as those with larger varus more hip adduction compared to healthy controls [41]. Gait alignment, have greater hip adduction [19, 20]. This along retraining reduced pelvic drop in 24% and reduced pain in with the muscle training might have led to adaptations in runners with patellofemoral pain [42]. Since hip adduction the abductor muscles. However, this is very speculative and is related to closed-chain pelvic drop [9], the reduction in would need further investigation. Therefore, further studies pelvic drop found in the present study might contribute to are needed to better investigate the effects of hip and trunk clinical improvements. In addition, a similar rationale strengthening in people with larger varus alignment. At this can be applied for the increase in pelvic drop observed point, caution is advised in the use of the studied muscle in the larger varus subgroup (average increase of 0.56 ). strengthening program for individuals with larger FAC varus It is also possible that this small change could be poten- alignment, considering the possible increase in pelvic drop. tially harmful [5, 6]. However, this needs to be subjected The increases in hip (external rotator) passive torque and to further investigation. active concentric and eccentric torques in the intervention Some limitations of the present study can be pointed out. group did not influence hip excursion in the frontal and First, there is a technical difficulty to adequately capture thigh transverse planes and pelvis excursion in the transverse kinematics, especially in the transverse plane, due to large plane. Perhaps, the implementation of neuromuscular train- errors related to soft tissue artifacts [25, 43]. In addition to ing during walking and/or the use of weight-bearing exercises its contribution to greater data variability, this difficulty performed in conditions more similar to the stance phase of may have prevented the detection of strengthening effects walking could produce more consistent results. These in hip kinematics. Unfortunately, this is a limitation of the 10 Applied Bionics and Biomechanics noninvasive motion-tracking procedure that is currently rec- Supplementary Materials ommended for hip kinematic assessment [43]. Another lim- Figure S1: measurement of foot-ankle complex varus align- itation was the nonrandom allocation of the participants in ment (forefoot-shank angle): (a) posterior view and (b) groups. Participants were allocated to groups according to lateral view [15]. Table S1: descriptive data (mean and stan- their availability to participate in the program (convenience dard deviation) of the kinematic and isokinetic variables method), which was necessary to make the study data collec- before and after the intervention for the intervention and tion feasible. Finally, only able-bodied and asymptomatic control groups and for the subgroups related to the foot- women participated in the study, which limits results’ gener- ankle complex varus alignment. (Supplementary Materials) alization. However, the study results may apply to programs that are aimed at preventing orthopedic problems in the lum- References bopelvic complex, in this population. Future studies could evaluate the effect of hip and trunk muscle strengthening in [1] K. R. Snyder, J. E. Earl, K. M. O’Connor, and K. T. 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