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The Influence of External Additional Loading on the Muscle Activity and Ground Reaction Forces during Gait

The Influence of External Additional Loading on the Muscle Activity and Ground Reaction Forces... Hindawi Applied Bionics and Biomechanics Volume 2021, Article ID 5532012, 10 pages https://doi.org/10.1155/2021/5532012 Research Article The Influence of External Additional Loading on the Muscle Activity and Ground Reaction Forces during Gait 1 1 2 Bartłomiej Zagrodny , Michał Ludwicki , and Wiktoria Wojnicz Department of Automation, Biomechanics and Mechatronics, Faculty of Mechanical Engineering, Łódź University of Technology, 1/15 Stefanowskiego Str. 90-924 Łódź, Poland Faculty of Mechanical Engineering and Ship Technology, Gdansk University of Technology, 11/12 Narutowicza Str. 80-233 Gdańsk, Poland Correspondence should be addressed to Michał Ludwicki; michal.ludwicki@p.lodz.pl Received 14 April 2021; Revised 28 June 2021; Accepted 10 July 2021; Published 29 July 2021 Academic Editor: Fuhao Mo Copyright © 2021 Bartłomiej Zagrodny 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. Asymmetrical external loading acting on the musculoskeletal system is generally considered unhealthy. Despite this knowledge, carrying loads in an asymmetrical manner like carrying on one shoulder, with one hand, or on the strap across the torso is a common practice. This study is aimed at presenting the effects of the mentioned load carrying methods on muscle activity assessed by using thermal field and ground reaction forces. Infrared thermography and pedobarographic force platform (ground reaction force/pressure measurement) were used in this study. Experimental results point out an increased load-dependent asymmetry of temperature distribution on the chosen areas of torso and the influence of external loading on ground reaction forces. Results point out that wearing an asymmetrical load should be avoided and are showing which type of carrying the external load is potentially less and the most harmful. 1. Introduction ground reaction forces (GRFs) during normal gait. It means that in nonpathological cases, the ground reaction forces In a human body, there may exist physiological asymmetries for the left and right lower limb should be similar. Lack of in the musculoskeletal system at the level that we assume still GRF symmetry for both lower limbs can be linked with mus- cle imbalance or some problems with the nervous and/or in range of norm or already pathological. They can be under- stood as faulty posture (like scoliosis and different leg musculoskeletal system (like joint degeneration, injuries [2], or asymmetrical body load [3] caused by external factors). lengths) or connected with the kinetics of movement (when speaking about asymmetrical gait—different step lengths or Furthermore, the muscle activity should be symmetrical in ground reaction forces). Generally, almost any asymmetry the case of symmetrical loading. In contrary, asymmetrical loading causes asymmetrical muscle activation to compen- in the musculoskeletal system is seen as a defect. One has to know that the problem can be increased by loading a body sate for the influence of asymmetry [4]. with asymmetrical, external loading. This can have a short- Muscle contraction leads to increased blood flow to sup- or long-term negative effect on posture correctness and/or ply the activated muscles with all necessary nutrients and static and dynamical stability. It can cause an injury or oxygen as well as to remove metabolites [5, 6] and to cool the muscles down. The energy produced by muscles is mainly degeneration of muscles or joints. The consequence of that can be joints’ kinematic and kinetic imbalance and body seg- dissipated in the form of heat (up to 70% [7]) and is caused ments or components of the musculoskeletal system, either by its relatively low mechanical efficiency. In the thermal reg- active and passive tissues, leading to an injury [1]. The mus- ulation process, one of the important elements is the skin. It cular system of a healthy human undergoing symmetrical plays an important role, and due to vasoconstriction, sweat- ing, and shivering [8, 9], the human body can regulate the external loading should produce relatively symmetrical 2 Applied Bionics and Biomechanics most significant muscles involved in maintaining the correct temperature of the body shell and core. By observing the skin temperature, the most and less active surface skeletal muscles posture. An InfReC R300SR-S thermal camera (NEC-Avio, can be selected. Some works point out that with the use of the Japan, FPA-type sensor, spectral range 8−14·10−6 m and infrared technique (IRT), the level of muscle activity in sport NETD 0.08 K) was used. The supplementary data were and during daily activity can be estimated [10, 11]. To do obtained from a pedobarographic force platform 1.5 m long this, mainly an infrared camera is the most common choice with an additional 6 m walkway (Footscan, RSscan Interna- [12–16]. It is possible to assess muscle activity even at a low tional, 12288 sensors in a 192 × 64 matrix, frequency up to level of their activity [17]. In the literature, one can find that 200 Hz). Additionally, a motorised treadmill (York Fitness) temperature differences below 1 C are also considered, and was employed in this study. when the experiments are carried out under controlled con- Experiments were done in monitored conditions, accord- ditions, the thermal results are treated as scientifically signif- ing to the protocol described in detail in [17]. All objects with icant [15, 18]. The thermal imaging technique proves also its high reflectance or temperature were removed from the sur- usability in detecting asymmetrical muscle activity. In work rounding. The ambient laboratory temperature could be cho- [19], the influence of additional loads on chosen gait param- sen by the volunteer prior to the experiment in the range of ° ° eters and muscle activity was done with the meaning of ther- 21 C–24 C. The humidity was in the range of 30%–45% RH mal imaging and optoelectronic system. (depending on the external conditions). No humidifiers or In contrary to another popular method—surface electro- air-dryers were used. Both parameters were monitored during myography (sEMG), which allows determining the level of each experiment, stored, and used in further analysis. Air muscle activation by the meaning of electrical signals [20, movement in the laboratory was minimised. Each participant 21], IRT is a noncontact technique and allows observing had 20 minutes of thermal adaptation. The skin emissivity the whole body, not the muscles chosen a priori. was set to 0.98. In each case, the skin was free of tattoo, inflam- Recording of ground reaction forces (GRFs) is widely mation, or other types of dermatological or vascular problems. used to examine a normal and pathological gait [22–24]. To improve the reliability of the experiments, it was decided to The influence of different types of additional external askvolunteerstofulfil all additional restrictions described in loading on muscle activation has been determined in numer- [17]. The protocol is presented in detail in Supplementary ous studies. Load in a form of a hockey bag of different sizes Materials in Tables S1 and S2. The inclusion criteria for [25] or a backpack worn in different positions [26–29] was volunteers were as follows: male, age 20–27 years, and body examined. The influence of carrying an additional load in core temperature below 37 C. The exclusion criteria were as one or both hands in the range from 5 up to 30 kg on muscle follows: diagnosed neurological problems, cardiovascular drug activation was investigated in work [30]. In all aforemen- treatment, leg length difference greater than 0.5 cm, failure to tioned papers, muscle activity was assessed by sEMG. comply with the preparation rules of thermal imaging A bag is currently a common way of carrying the load. examination, skin inflammation, and visible “hot spots” on People keep them in hand, or hanging on the strap, put on the body in IR, or failure to pass the restricted Romberg test. the shoulders as support, or put a long strap across their Nine healthy male university students volunteered in this torso. Carrying backpacks on one shoulder is also popular experiment. All were without any injuries, neuromusculoskele- among the young generation [31]. These four methods of tal disorders, and visible asymmetry/faulty posture. To check carrying additional loads have been examined. for scoliosis, the Addams manoeuvre was used. Their age was This study is aimed at determining the relationship in the range 23:5±2:5;height, 181:1± 6:5cm; body weight, between different types of external asymmetrical musculo- 78:0±18:5kg;and body mass index, 23:7±4:2 kg/m .All par- skeletal loading (backpack on one shoulder, bag in one hand, ticipants declared as right hand and right leg dominant. Volun- bag on one shoulder, and bag with the strap across the torso, teers were instructed to walk barefoot during all trials. The with an additional linear distributed load normalized to the experiment was organized according to the Helsinki regulation, body weight of 5%, 10%, and 15%) and asymmetry of muscle and all participants were informed in detail about its aim, scope, activity assessed by using thermal fields of the torso chosen and procedure and signed the written consent, accepted by the areas (trapezius, latissimus dorsi, and obliquus abdominis). local ethical board (Committee of Research Ethics with Human That asymmetrical external load influences human posture Participation at Gdansk University of Technology). and can be treated as a preliminary study as limited to young Each participant was assigned randomly to carry the addi- male volunteers. The additional loading is treated as an tional load in one of four different ways, as shown in Figure 1, external perturbation. According to [32], it is important to i.e., respectively: (a) backpack on one shoulder (backpack), (2) gain a broader knowledge in the field of muscle coordination bag in one hand (bag one hand), (3) bag on one shoulder (bag in daily life, especially when the musculoskeletal system shoulder), and (4) bag with the strap across the torso (bag undergoes different types of perturbations. across), with an additional linear distributed load normalized to their body weight of 5%, 10%, and 15% (as in work [3]), 2. Materials and Methods as well as to perform a control gait without an additional load to determine the effects of each load. Infrared thermography was used to assess torso muscle The experimental procedure was identical for each par- activity. The muscles chosen for analysis are right and left latissimus dorsi, right and left trapezius, and right and left ticipant and was as follows: firstly, volunteers were asked to remove clothing from the upper body and to acclimate for obliquus abdominis. They were selected as the biggest and Applied Bionics and Biomechanics 3 (a) (b) (c) (d) Figure 1: Four investigated methods of carrying the load: (a) backpack on one shoulder, (b) bag in one hand, (c) bag on one shoulder, and (d) bag with strap across torso. 20 minutes to obtain stable skin temperature. Next, initial Each sequence of mentioned measures (one type of carry- upper-body thermograms were taken (anterior and posterior ing the load with given level) took approximately 45 minutes side of the torso) with the thermal camera positioned 3 m away per person. The next weight/load type combination was done from subjects on a tripod. Then, volunteers were asked to walk on a different day to minimise the influence of each set on on a pedobarographic force platform with the same load and another one. type of carrying as it was done for thermal imaging. Next, the The results of thermal imaging were analysed in the ded- main task starts (within 30 s) with a gait on a motorised tread- icated software InfReC Analyzer NS9500 Standard. For each mill for a 1 km distance with a velocity equal to 4 km/h. This volunteer, the areas of the left and right trapezius, latissimus speed was chosen as an average, comfortable speed for most dorsi, and obliquus abdominis were marked as shown in of the volunteers after pretrials, which is slower by 0.5 km/h Figure 2(a). Additionally, the whole trunk skin average tem- than the comfortable speed on a treadmill mentioned in [17] perature was measured just before (second thermogram) and as a result of a natural tendency to walk slower when carrying 5 minutes after gait (third thermogram), separately for the a load [4]. A second thermogram was taken right after the gait ventral and dorsal part of the torso. The results presented sequence (also within 30 s; this time takes to move from the as the change of average temperature were calculated as the front of camera to the treadmill). A third thermal image was difference of average temperatures between the right and taken 5 minutes after the second one due to the presence of the left muscle, before and after each experiment (first and sweat on the skin after the activity (especially in places where second thermogram). the bag strap contacts the skin). It is worth noticing that due The results for the pedobarographic force platform were to thermoregulation and especially sweating which has a cool- also analysed in dedicated software, later exported for further ing effect on the skin [33], it was decided to examine the asym- calculations. Volunteers performed 5 crossings on a pedobaro- metry of temperature distribution and changes of this graphic force platform. For further analysis, automatically cal- asymmetry as an indicator of uneven loading of the left and culated average results of these 5 crossings were used. Walk on right muscle part (difference: left − right). the pedobarographic force platform was performed just after 4 Applied Bionics and Biomechanics WA PO C 400 MS D C F E 0 100 200 300 400 500 600 700 800 Time (ms) (a) (b) Figure 2: (a) Exemplary thermal image of a volunteer with muscles marked in the software: A/B—trapezius (right/left), C/D—latissimus dorsi (right/left), and E/F—obliquus abdominis (left/right). (b) Chosen results of ground reaction forces. finishing the first thermal imaging with the same weight/load the bag held on one shoulder with 10% of body load type combination. Three ground reaction forces were consid- (10% increase). ered (see Figure 2(b)): maximal weight acceptance force In the case of the latissimus dorsi and obliquus abdominis (WA), force in midstance (MS) (local minimum), and maxi- with additional external loading on the right side, the left side mal force in push-off gait phase (PO). of the muscles was warmer in comparison to the right side. In Using the Shapiro-Wilk test, a normality of data distribu- the case of the trapezius muscle, we can observe an opposite tion was verified. To set linear relationships for normal phenomenon, and this can be explained by the scapula and distributed groups, the Pearson correlation coefficient r was clavicle stabilization done by this muscle. defined by considering the statistical significance threshold p =0:1.Todefine linear relationships for nonnormal distrib- 3.2. Pedobarographic Examination. Figures 6–8 are present- uted groups, the Spearman correlation coefficient r was used ing the percentage ratio of maximal weight acceptance force by assuming the statistical significance threshold p =0:05. (WA) (Figure 6), maximal force in midstance (MS) Linear regressions were set between three measured muscle (Figure 7), and maximal force in push-off (PO) (Figure 8) group temperature mean differences (left side minus right side) as averages for all volunteers with standard deviations. The and three measured ground reaction forces (WA, MS and PO). value “both” means an average for the left and right site. The statistical calculations were performed by using the Stat- Results for all types of load are presented regarding Soft Statistica 13.1 package. Trying to classify the strength of each time to the nonloaded case. As it can be observed, the correlation relationship, we adopted the following ranges, an increase in WA, MS, and PO forces is visible in all cases givenin[34]: ð0; 0:2—poor, ð0:2;0:5—fair, ð0:5;0:7 of external loading. The WA was the highest in the case —moderate, ð0:7;0:9—very strong, and ð0:9;1:0—perfect. when the bag was carried in one hand. This result can indi- cate the impact of this type of carrying on the gait dynam- ics and its stability [35]. 3. Results The highest values for MS are obtained for the bag carried on one shoulder, and the lowest are surprisingly for the bag 3.1. Thermal Imaging. Results of thermal measurements were assessed as average values with standard deviations for all carried in one hand. The hypothesis is put forward; it relates volunteers (Figures 3–5). They should be interpreted as an to balance in the frontal plane, but it needs deeper investiga- tion. In the case of PO force, it cannot be distinguished by asymmetry of temperature distribution on the chosen muscle area (trapezius—right/left, latissimus dorsi—right/left, and any dominant type of load/carrying method that generates the highest values; thus, only a graduation from the lowest obliquus abdominis—left/right) after the exercise. In each case, the reference level was a thermal image done just before to highest values is seen, dependent on the value of external the experiment, after acclimatization. The presented values loading. There is no statistically significant difference for the majority of cases between the forces recorded for the left are relative and calculated as difference: left ðLÞ − right ðRÞ. The initial asymmetry in temperature distribution varies or right leg; similar conclusions are published in paper [12]. from 0.04 K for the obliquus abdominis and 0.07 K for the latissimus dorsi up to 0.11 K for the trapezius muscle. The 3.3. Relationship Investigation. According to the tests highest differences after the experiment were reached for performed, it was defined that 104/108 samples related to thermal parameters and force parameters have normal distri- the obliquus abdominis (Figure 5) 15% load carried on the shoulder (0.37 K). For the latissimus dorsi (Figure 3), the butions. In Table 1 are given statistically significant results highest asymmetry was observed in the case of 10% load, for one side (right or left) or both sides between thermal bag in one hand (0.2 K), and slightly less for bag on one parameters (trapezius (right/left), latissimus dorsi (right/left), shoulder with 5% of the load (0.19 K). For the trapezius and obliquus abdominis (left/right)) and force parameters (m (Figure 4) muscle, the highest asymmetry was observed for aximal weight acceptance force (WA), maximal force in Force (N) Applied Bionics and Biomechanics 5 Bag shoulder Bag one hand Bag across Back pack –0.20 –0.15 –0.10 –0.05 0.00 0.05 0.10 0.15 0.20 0.25 Differences in temperatures (K) 15% 5% 10% 0% Figure 3: Average differences for latissimus in the function of normalized load. Bag shoulder Bag one hand Bag across Back pack –0.20 –0.10 0.00 0.10 0.20 0.30 0.40 0.50 Differences in temperatures (K) 15% 5% 10% 0% Figure 4: Average differences for trapezius in the function of normalized load. Bag shoulder Bag one hand Bag across Back pack –0.20 –0.10 0.00 0.10 0.20 0.30 0.40 0.50 Differences in temperatures (K) 15% 5% 10% 0% Figure 5: Average differences for obliquus abdominis in the function of normalized load. Percentage of load normalised to the Percentage of load normalised to the Percentage of load normalised to the body weight (%) body weight (%) body weight (%) 6 Applied Bionics and Biomechanics 5% 5% 5% 10% 10% 10% 15% 15% 15% left right both left right both left right both Backpack Bag shoulder Bag one hand Bag across Figure 6: Maximal weight acceptance changes for the left, right, and average of both (left and right side) for different levels of additional load. 5% 5% 5% 10% 10% 10% 15% 15% 15% left right both left right both left right both Backpack Bag shoulder Bag one hand Bag across Figure 7: Midstance force changes for the left, right, and average of both (left and right side) for different levels of additional load. ff 5% 5% 5% 10% 10% 10% 15% 15% 15% left right both left right both left right both Backpack Bag shoulder Bag one hand Bag across Figure 8: Push-off forces for the left, right, and average of both (left and right side) for different levels of additional load. Average percentage difference in weight Average percentage difference in push o acceptance (%) (%) Average percentage difference in mid stance (%) Applied Bionics and Biomechanics 7 Table 1: Statistical relationships between thermal and force parameters for three muscle groups: trapezius (TT), latissimus dorsi (TL), and obliquus abdominis (TO), and three ground reaction force values: maximal weight acceptance force (WA), maximal force in midstance (MS), and maximal force in push-off gait phase (PO), for the left and right leg, respectively. Significant relations (p <0:1 or p <0:05 for Spearman’s test) are written in bold. Left side Right side Load (%) Load type Force Muscle ∗ 2 ∗ 2 r or r pr description r r or r pr description r 5% Backpack MS TL -0.757 0.018 Very strong negative 0.573 0.311 0.415 Fair positive 0.097 5% Backpack MS TT -0.233 0.547 Fair negative 0.054 0.878 0.002 Very strong positive 0.771 5% Backpack PO TL -0.852 0.004 Very strong negative 0.726 0.881 0.002 Very strong positive 0.777 5% Backpack WA TO 0.691 0.039 Moderate positive 0.477 0.123 0.753 Poor positive 0.015 10% Backpack PO TL 0.351 0.354 Fair positive 0.123 -0.629 0.069 Moderate negative 0.396 10% Backpack WA TL 0.177 0.649 Poor positive 0.031 -0.805 0.009 Very strong negative 0.649 15% Backpack MS TT 0.134 0.731 Poor positive 0.018 -0.867 0.002 Very strong negative 0.752 15% Backpack WA TT 0.135 0.729 Poor positive 0.018 -0.621 0.075 Moderate negative 0.385 15% Bag across MS TO -0.707 0.033 Very strong negative 0.500 0.586 0.097 Moderate positive 0.344 15% Bag across PO TL -0.696 0.037 Moderate negative 0.485 0.130 0.739 Poor positive 0.017 15% Bag across WA TL -0.382 0.311 Fair negative 0.146 0.733 0.025 Very strong positive 0.537 15% Bag across WA TO -0.334 0.380 Fair negative 0.111 0.711 0.032 Very strong positive 0.505 5% Bag one hand PO TT 0.378 0.209 Fair positive 0.143 -0.585 0.098 Moderate negative 0.342 15% Bag one hand MS TL -0.756 <0.05 Very strong negative — 0.235 >0.05 Fair positive — 15% Bag one hand MS TT 0.031 0.937 Poor positive 0.001 -0.599 0.088 Moderate negative 0.359 15% Bag one hand PO TL -0.807 <0.05 Very strong negative — 0.521 >0.05 Moderate positive — 15% Bag one hand WA TL -0.277 >0.05 Fair negative — 0.731 <0.05 Very strong positive — 15% Bag one hand WA TT 0.636 0.066 Moderate positive 0.404 -0.026 0.947 Poor negative 0.001 5% Bag shoulder MS TO 0.792 0.011 Very strong positive 0.628 -0.385 0.306 Fair negative 0.148 15% Bag shoulder MS TL 0.586 0.097 Moderate positive 0.343 -0.240 0.534 Fair negative 0.058 15% Bag shoulder MS TO 0.329 0.387 Fair positive 0.108 -0.641 0.063 Moderate negative 0.411 15% Bag shoulder PO TO 0.673 0.047 Moderate positive 0.453 -0.259 0.501 Fair negative 0.067 15% Bag shoulder PO TT -0.373 0.322 Fair negative 0.139 0.750 0.020 Very strong positive 0.562 15% Bag shoulder WA TO 0.757 0.018 Very strong positive 0.573 -0.132 0.736 Poor negative 0.017 As expected, almost any asymmetrical load induces an midstance (MS), and maximal force in push-off gait phase (PO)). For normal distributed sets, the Pearson coefficients increase in the asymmetry of temperature distribution, and generally, it can be stated that higher asymmetrical load and coefficient of determination r are given (p =0:1). For nonnormal distributed sets, the Spearman coefficients are causes higher asymmetry in temperature distribution. The main exception to the rule is the case of the highest presented (p =0:05). load—15% of the body mass. It can be assumed that the addi- tional load influences the position of the center of mass which changes the kinematics of the body and excessive 4. Discussion physical effort causes sweating, and this influences the tem- The experiment was focused on the effects of an asymmetri- perature distribution. Similar phenomena were observed in other works [36, 37]. cal load on the work of trunk muscles and differences in ground reaction forces. In particular, the asymmetry of tem- Results reveal asymmetrical muscle work caused by their perature distribution was observed (Figures 3–5). The high- asymmetric activity and force production caused by an asym- est differences were reached for the obliquus abdominis in metric external load. A similar testing procedure to the pre- the case of 15% load carried on the shoulder (0.37 K) and sented one was done in work [38], but the technique of for the latissimus dorsi for 10% load in the case of a bag car- muscle activity recording was surface electromyography. ried in one hand (0.2 K), and it was slightly less for a bag on Results in the mentioned study pointed out statistically sig- one shoulder with 5% of the load (0.19 K). For the trapezius nificant differences only for the trapezius and erector spinae muscle, the highest asymmetry was reached for the bag car- but not statistically significant differences in latissimus dorsi ried on one shoulder with 10% of body load (10% increase). and obliquus abdominis activity. Based on those results, we can assume that a COM Results presented in this study showed such dependence (center of mass) translation and compensation of the asym- in all cases except for the cross-body bag. However, one metrical load cause a counterbalance of spine lateral flexion might try to define nonlinear relationships between thermal and lead to asymmetrical trunk muscle activation. and ground reaction force parameters, but this demands to 8 Applied Bionics and Biomechanics linear correlations is similar to those identified for the bag test a bigger number of subjects. According to the experiment carried out and presented in the paper [39], the biggest differ- carried in one hand but mostly for the left side of the body ences should be visible for the volunteer carrying a bag in the and for the obliquus abdominis muscle (see Table 1). Considering a bag carried across the body (on the right position lower than the level of the shoulder. In this study, this is not proven. For most volunteers, it may be concluded side) (the best one), one can induce that external load is sta- that the posture is not exactly symmetrical according to the bilized, and that is why this is the less fatigable position. sagittal plane and this is perfectly normal. Increased activation of contraction of the opposite trapezius Additional COM translation verification may be consid- and abdominis should be expected. ered here, e.g., by using motion capture or IMU systems [40]. The bigger number of statistically significant linear corre- The results of the experiment carried out with children’s lations was obtained for the left side and only for obliquus participation [41] prove the asymmetrical muscle activity abdominis and latissimus dorsi muscles (see Table 1). among those with the problem of scoliosis with one curve as well as double curve one. In the presented study, the tem- 5. Conclusions perature difference between right and left muscles before any activity is positive value and shows an asymmetrical muscle Obtained results show that during gait with an additional activity. Generally, the trapezius muscle is increasingly acti- load held asymmetrically, the symmetry of muscle force pro- vated with increasing external load on the right side. If the duction changes. With the increasing weight of the carried load is not distributed bilaterally, there is an increased muscle load, the differences of temperature become higher; however, activity of the superior part of the trapezius on the side that different types of loading cause different patterns of the bag is worn on. The same conclusion was found in the compensation and influence the ground reaction forces in publication [38]. In all examined cases where the additional different ways. load was distributed nonuniformly, the trapezius was more A general observation allows us to make a statement. that activated on the side where the strap was held on. This is in the case of the asymmetrical way of carrying the external probably due to the volunteers trying to maintain the proper load, the less harmful for the musculoskeletal system seems scapula and clavicle position to ensure the strap of the bag is to be the placing the strap across the torso because in this kept over the shoulder while the trunk is laterally flexed so case, the smallest increase in temperature asymmetry was that the center of mass of the body remains over the support observed. On the other hand, the worst method is to keep area during gait. the load in one hand or on the shoulder especially when we The asymmetry of GRFs is revealed in Figures 6–8. Gen- use to carry the load only one side almost every time—in this erally, the highest asymmetry is obtained for MS forces. case, the highest increase in temperature asymmetry was Based on the obtained results and those found in literature, present. we can assume that a COM translation and compensation Generally, it should be underlined that the results of the asymmetrical load present in a form of counterbalance indicate that walking with the asymmetric load inducts cause spine lateral flexion and result in asymmetrical trunk compensation made by muscles and posture and increases muscle activation. Repeating this type of asymmetrical load- the possibility of muscle injury and leads to or increases ing of the musculoskeletal system is linked with greater shear faulty posture, even if this study will be treated as a prelimi- and compressive forces present in the spine [37]. The authors nary study, limited to relatively young and fit males. of [37] pointed out also that “asymmetric lifting is more stressful than frontally symmetric lifting.” Considering the backpack load type (carried on the right Data Availability side of the body), increased activation of the right abdominis and right latissimus muscles should be expected. The bigger The thermography image data and pedobarographic force number of statistically significant linear correlations was platform data used to support the findings of this study are obtained for the right side, mostly for the trapezius and latis- available from the corresponding author upon request. simus dorsi muscles (see Table 1). Considering a bag carried in the right hand, increased activation of the right opposite trapezius, latissimus, and Conflicts of Interest abdominis should be expected. The position of external load with respect to the COM of the body is the most distant with The authors declare that there is no conflict of interest respect to the other configurations of the load, and that is regarding the publication of this paper. why one should expect that this carrying could be the most fatigable ones. To avoid fatigue, the musculoskeletal should activate different muscle groups, and that is why the lowest Acknowledgments number of statistically significant linear correlation (for trapezius and latissimus dorsi muscles) was found in this case We want to thank students Anna Frątczak, Angelika (see Table 1). Puchalska, Jarosław Chruściel, and Siam Streibl for their help Considering a bag carried on right shoulder, increased in preparation and conducting experiments. This paper was activation of the right trapezius, abdominis, and latissimus supported by the Grant for Young Scientists Lodz University should be expected. 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The Influence of External Additional Loading on the Muscle Activity and Ground Reaction Forces during Gait

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Hindawi Applied Bionics and Biomechanics Volume 2021, Article ID 5532012, 10 pages https://doi.org/10.1155/2021/5532012 Research Article The Influence of External Additional Loading on the Muscle Activity and Ground Reaction Forces during Gait 1 1 2 Bartłomiej Zagrodny , Michał Ludwicki , and Wiktoria Wojnicz Department of Automation, Biomechanics and Mechatronics, Faculty of Mechanical Engineering, Łódź University of Technology, 1/15 Stefanowskiego Str. 90-924 Łódź, Poland Faculty of Mechanical Engineering and Ship Technology, Gdansk University of Technology, 11/12 Narutowicza Str. 80-233 Gdańsk, Poland Correspondence should be addressed to Michał Ludwicki; michal.ludwicki@p.lodz.pl Received 14 April 2021; Revised 28 June 2021; Accepted 10 July 2021; Published 29 July 2021 Academic Editor: Fuhao Mo Copyright © 2021 Bartłomiej Zagrodny 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. Asymmetrical external loading acting on the musculoskeletal system is generally considered unhealthy. Despite this knowledge, carrying loads in an asymmetrical manner like carrying on one shoulder, with one hand, or on the strap across the torso is a common practice. This study is aimed at presenting the effects of the mentioned load carrying methods on muscle activity assessed by using thermal field and ground reaction forces. Infrared thermography and pedobarographic force platform (ground reaction force/pressure measurement) were used in this study. Experimental results point out an increased load-dependent asymmetry of temperature distribution on the chosen areas of torso and the influence of external loading on ground reaction forces. Results point out that wearing an asymmetrical load should be avoided and are showing which type of carrying the external load is potentially less and the most harmful. 1. Introduction ground reaction forces (GRFs) during normal gait. It means that in nonpathological cases, the ground reaction forces In a human body, there may exist physiological asymmetries for the left and right lower limb should be similar. Lack of in the musculoskeletal system at the level that we assume still GRF symmetry for both lower limbs can be linked with mus- cle imbalance or some problems with the nervous and/or in range of norm or already pathological. They can be under- stood as faulty posture (like scoliosis and different leg musculoskeletal system (like joint degeneration, injuries [2], or asymmetrical body load [3] caused by external factors). lengths) or connected with the kinetics of movement (when speaking about asymmetrical gait—different step lengths or Furthermore, the muscle activity should be symmetrical in ground reaction forces). Generally, almost any asymmetry the case of symmetrical loading. In contrary, asymmetrical loading causes asymmetrical muscle activation to compen- in the musculoskeletal system is seen as a defect. One has to know that the problem can be increased by loading a body sate for the influence of asymmetry [4]. with asymmetrical, external loading. This can have a short- Muscle contraction leads to increased blood flow to sup- or long-term negative effect on posture correctness and/or ply the activated muscles with all necessary nutrients and static and dynamical stability. It can cause an injury or oxygen as well as to remove metabolites [5, 6] and to cool the muscles down. The energy produced by muscles is mainly degeneration of muscles or joints. The consequence of that can be joints’ kinematic and kinetic imbalance and body seg- dissipated in the form of heat (up to 70% [7]) and is caused ments or components of the musculoskeletal system, either by its relatively low mechanical efficiency. In the thermal reg- active and passive tissues, leading to an injury [1]. The mus- ulation process, one of the important elements is the skin. It cular system of a healthy human undergoing symmetrical plays an important role, and due to vasoconstriction, sweat- ing, and shivering [8, 9], the human body can regulate the external loading should produce relatively symmetrical 2 Applied Bionics and Biomechanics most significant muscles involved in maintaining the correct temperature of the body shell and core. By observing the skin temperature, the most and less active surface skeletal muscles posture. An InfReC R300SR-S thermal camera (NEC-Avio, can be selected. Some works point out that with the use of the Japan, FPA-type sensor, spectral range 8−14·10−6 m and infrared technique (IRT), the level of muscle activity in sport NETD 0.08 K) was used. The supplementary data were and during daily activity can be estimated [10, 11]. To do obtained from a pedobarographic force platform 1.5 m long this, mainly an infrared camera is the most common choice with an additional 6 m walkway (Footscan, RSscan Interna- [12–16]. It is possible to assess muscle activity even at a low tional, 12288 sensors in a 192 × 64 matrix, frequency up to level of their activity [17]. In the literature, one can find that 200 Hz). Additionally, a motorised treadmill (York Fitness) temperature differences below 1 C are also considered, and was employed in this study. when the experiments are carried out under controlled con- Experiments were done in monitored conditions, accord- ditions, the thermal results are treated as scientifically signif- ing to the protocol described in detail in [17]. All objects with icant [15, 18]. The thermal imaging technique proves also its high reflectance or temperature were removed from the sur- usability in detecting asymmetrical muscle activity. In work rounding. The ambient laboratory temperature could be cho- [19], the influence of additional loads on chosen gait param- sen by the volunteer prior to the experiment in the range of ° ° eters and muscle activity was done with the meaning of ther- 21 C–24 C. The humidity was in the range of 30%–45% RH mal imaging and optoelectronic system. (depending on the external conditions). No humidifiers or In contrary to another popular method—surface electro- air-dryers were used. Both parameters were monitored during myography (sEMG), which allows determining the level of each experiment, stored, and used in further analysis. Air muscle activation by the meaning of electrical signals [20, movement in the laboratory was minimised. Each participant 21], IRT is a noncontact technique and allows observing had 20 minutes of thermal adaptation. The skin emissivity the whole body, not the muscles chosen a priori. was set to 0.98. In each case, the skin was free of tattoo, inflam- Recording of ground reaction forces (GRFs) is widely mation, or other types of dermatological or vascular problems. used to examine a normal and pathological gait [22–24]. To improve the reliability of the experiments, it was decided to The influence of different types of additional external askvolunteerstofulfil all additional restrictions described in loading on muscle activation has been determined in numer- [17]. The protocol is presented in detail in Supplementary ous studies. Load in a form of a hockey bag of different sizes Materials in Tables S1 and S2. The inclusion criteria for [25] or a backpack worn in different positions [26–29] was volunteers were as follows: male, age 20–27 years, and body examined. The influence of carrying an additional load in core temperature below 37 C. The exclusion criteria were as one or both hands in the range from 5 up to 30 kg on muscle follows: diagnosed neurological problems, cardiovascular drug activation was investigated in work [30]. In all aforemen- treatment, leg length difference greater than 0.5 cm, failure to tioned papers, muscle activity was assessed by sEMG. comply with the preparation rules of thermal imaging A bag is currently a common way of carrying the load. examination, skin inflammation, and visible “hot spots” on People keep them in hand, or hanging on the strap, put on the body in IR, or failure to pass the restricted Romberg test. the shoulders as support, or put a long strap across their Nine healthy male university students volunteered in this torso. Carrying backpacks on one shoulder is also popular experiment. All were without any injuries, neuromusculoskele- among the young generation [31]. These four methods of tal disorders, and visible asymmetry/faulty posture. To check carrying additional loads have been examined. for scoliosis, the Addams manoeuvre was used. Their age was This study is aimed at determining the relationship in the range 23:5±2:5;height, 181:1± 6:5cm; body weight, between different types of external asymmetrical musculo- 78:0±18:5kg;and body mass index, 23:7±4:2 kg/m .All par- skeletal loading (backpack on one shoulder, bag in one hand, ticipants declared as right hand and right leg dominant. Volun- bag on one shoulder, and bag with the strap across the torso, teers were instructed to walk barefoot during all trials. The with an additional linear distributed load normalized to the experiment was organized according to the Helsinki regulation, body weight of 5%, 10%, and 15%) and asymmetry of muscle and all participants were informed in detail about its aim, scope, activity assessed by using thermal fields of the torso chosen and procedure and signed the written consent, accepted by the areas (trapezius, latissimus dorsi, and obliquus abdominis). local ethical board (Committee of Research Ethics with Human That asymmetrical external load influences human posture Participation at Gdansk University of Technology). and can be treated as a preliminary study as limited to young Each participant was assigned randomly to carry the addi- male volunteers. The additional loading is treated as an tional load in one of four different ways, as shown in Figure 1, external perturbation. According to [32], it is important to i.e., respectively: (a) backpack on one shoulder (backpack), (2) gain a broader knowledge in the field of muscle coordination bag in one hand (bag one hand), (3) bag on one shoulder (bag in daily life, especially when the musculoskeletal system shoulder), and (4) bag with the strap across the torso (bag undergoes different types of perturbations. across), with an additional linear distributed load normalized to their body weight of 5%, 10%, and 15% (as in work [3]), 2. Materials and Methods as well as to perform a control gait without an additional load to determine the effects of each load. Infrared thermography was used to assess torso muscle The experimental procedure was identical for each par- activity. The muscles chosen for analysis are right and left latissimus dorsi, right and left trapezius, and right and left ticipant and was as follows: firstly, volunteers were asked to remove clothing from the upper body and to acclimate for obliquus abdominis. They were selected as the biggest and Applied Bionics and Biomechanics 3 (a) (b) (c) (d) Figure 1: Four investigated methods of carrying the load: (a) backpack on one shoulder, (b) bag in one hand, (c) bag on one shoulder, and (d) bag with strap across torso. 20 minutes to obtain stable skin temperature. Next, initial Each sequence of mentioned measures (one type of carry- upper-body thermograms were taken (anterior and posterior ing the load with given level) took approximately 45 minutes side of the torso) with the thermal camera positioned 3 m away per person. The next weight/load type combination was done from subjects on a tripod. Then, volunteers were asked to walk on a different day to minimise the influence of each set on on a pedobarographic force platform with the same load and another one. type of carrying as it was done for thermal imaging. Next, the The results of thermal imaging were analysed in the ded- main task starts (within 30 s) with a gait on a motorised tread- icated software InfReC Analyzer NS9500 Standard. For each mill for a 1 km distance with a velocity equal to 4 km/h. This volunteer, the areas of the left and right trapezius, latissimus speed was chosen as an average, comfortable speed for most dorsi, and obliquus abdominis were marked as shown in of the volunteers after pretrials, which is slower by 0.5 km/h Figure 2(a). Additionally, the whole trunk skin average tem- than the comfortable speed on a treadmill mentioned in [17] perature was measured just before (second thermogram) and as a result of a natural tendency to walk slower when carrying 5 minutes after gait (third thermogram), separately for the a load [4]. A second thermogram was taken right after the gait ventral and dorsal part of the torso. The results presented sequence (also within 30 s; this time takes to move from the as the change of average temperature were calculated as the front of camera to the treadmill). A third thermal image was difference of average temperatures between the right and taken 5 minutes after the second one due to the presence of the left muscle, before and after each experiment (first and sweat on the skin after the activity (especially in places where second thermogram). the bag strap contacts the skin). It is worth noticing that due The results for the pedobarographic force platform were to thermoregulation and especially sweating which has a cool- also analysed in dedicated software, later exported for further ing effect on the skin [33], it was decided to examine the asym- calculations. Volunteers performed 5 crossings on a pedobaro- metry of temperature distribution and changes of this graphic force platform. For further analysis, automatically cal- asymmetry as an indicator of uneven loading of the left and culated average results of these 5 crossings were used. Walk on right muscle part (difference: left − right). the pedobarographic force platform was performed just after 4 Applied Bionics and Biomechanics WA PO C 400 MS D C F E 0 100 200 300 400 500 600 700 800 Time (ms) (a) (b) Figure 2: (a) Exemplary thermal image of a volunteer with muscles marked in the software: A/B—trapezius (right/left), C/D—latissimus dorsi (right/left), and E/F—obliquus abdominis (left/right). (b) Chosen results of ground reaction forces. finishing the first thermal imaging with the same weight/load the bag held on one shoulder with 10% of body load type combination. Three ground reaction forces were consid- (10% increase). ered (see Figure 2(b)): maximal weight acceptance force In the case of the latissimus dorsi and obliquus abdominis (WA), force in midstance (MS) (local minimum), and maxi- with additional external loading on the right side, the left side mal force in push-off gait phase (PO). of the muscles was warmer in comparison to the right side. In Using the Shapiro-Wilk test, a normality of data distribu- the case of the trapezius muscle, we can observe an opposite tion was verified. To set linear relationships for normal phenomenon, and this can be explained by the scapula and distributed groups, the Pearson correlation coefficient r was clavicle stabilization done by this muscle. defined by considering the statistical significance threshold p =0:1.Todefine linear relationships for nonnormal distrib- 3.2. Pedobarographic Examination. Figures 6–8 are present- uted groups, the Spearman correlation coefficient r was used ing the percentage ratio of maximal weight acceptance force by assuming the statistical significance threshold p =0:05. (WA) (Figure 6), maximal force in midstance (MS) Linear regressions were set between three measured muscle (Figure 7), and maximal force in push-off (PO) (Figure 8) group temperature mean differences (left side minus right side) as averages for all volunteers with standard deviations. The and three measured ground reaction forces (WA, MS and PO). value “both” means an average for the left and right site. The statistical calculations were performed by using the Stat- Results for all types of load are presented regarding Soft Statistica 13.1 package. Trying to classify the strength of each time to the nonloaded case. As it can be observed, the correlation relationship, we adopted the following ranges, an increase in WA, MS, and PO forces is visible in all cases givenin[34]: ð0; 0:2—poor, ð0:2;0:5—fair, ð0:5;0:7 of external loading. The WA was the highest in the case —moderate, ð0:7;0:9—very strong, and ð0:9;1:0—perfect. when the bag was carried in one hand. This result can indi- cate the impact of this type of carrying on the gait dynam- ics and its stability [35]. 3. Results The highest values for MS are obtained for the bag carried on one shoulder, and the lowest are surprisingly for the bag 3.1. Thermal Imaging. Results of thermal measurements were assessed as average values with standard deviations for all carried in one hand. The hypothesis is put forward; it relates volunteers (Figures 3–5). They should be interpreted as an to balance in the frontal plane, but it needs deeper investiga- tion. In the case of PO force, it cannot be distinguished by asymmetry of temperature distribution on the chosen muscle area (trapezius—right/left, latissimus dorsi—right/left, and any dominant type of load/carrying method that generates the highest values; thus, only a graduation from the lowest obliquus abdominis—left/right) after the exercise. In each case, the reference level was a thermal image done just before to highest values is seen, dependent on the value of external the experiment, after acclimatization. The presented values loading. There is no statistically significant difference for the majority of cases between the forces recorded for the left are relative and calculated as difference: left ðLÞ − right ðRÞ. The initial asymmetry in temperature distribution varies or right leg; similar conclusions are published in paper [12]. from 0.04 K for the obliquus abdominis and 0.07 K for the latissimus dorsi up to 0.11 K for the trapezius muscle. The 3.3. Relationship Investigation. According to the tests highest differences after the experiment were reached for performed, it was defined that 104/108 samples related to thermal parameters and force parameters have normal distri- the obliquus abdominis (Figure 5) 15% load carried on the shoulder (0.37 K). For the latissimus dorsi (Figure 3), the butions. In Table 1 are given statistically significant results highest asymmetry was observed in the case of 10% load, for one side (right or left) or both sides between thermal bag in one hand (0.2 K), and slightly less for bag on one parameters (trapezius (right/left), latissimus dorsi (right/left), shoulder with 5% of the load (0.19 K). For the trapezius and obliquus abdominis (left/right)) and force parameters (m (Figure 4) muscle, the highest asymmetry was observed for aximal weight acceptance force (WA), maximal force in Force (N) Applied Bionics and Biomechanics 5 Bag shoulder Bag one hand Bag across Back pack –0.20 –0.15 –0.10 –0.05 0.00 0.05 0.10 0.15 0.20 0.25 Differences in temperatures (K) 15% 5% 10% 0% Figure 3: Average differences for latissimus in the function of normalized load. Bag shoulder Bag one hand Bag across Back pack –0.20 –0.10 0.00 0.10 0.20 0.30 0.40 0.50 Differences in temperatures (K) 15% 5% 10% 0% Figure 4: Average differences for trapezius in the function of normalized load. Bag shoulder Bag one hand Bag across Back pack –0.20 –0.10 0.00 0.10 0.20 0.30 0.40 0.50 Differences in temperatures (K) 15% 5% 10% 0% Figure 5: Average differences for obliquus abdominis in the function of normalized load. Percentage of load normalised to the Percentage of load normalised to the Percentage of load normalised to the body weight (%) body weight (%) body weight (%) 6 Applied Bionics and Biomechanics 5% 5% 5% 10% 10% 10% 15% 15% 15% left right both left right both left right both Backpack Bag shoulder Bag one hand Bag across Figure 6: Maximal weight acceptance changes for the left, right, and average of both (left and right side) for different levels of additional load. 5% 5% 5% 10% 10% 10% 15% 15% 15% left right both left right both left right both Backpack Bag shoulder Bag one hand Bag across Figure 7: Midstance force changes for the left, right, and average of both (left and right side) for different levels of additional load. ff 5% 5% 5% 10% 10% 10% 15% 15% 15% left right both left right both left right both Backpack Bag shoulder Bag one hand Bag across Figure 8: Push-off forces for the left, right, and average of both (left and right side) for different levels of additional load. Average percentage difference in weight Average percentage difference in push o acceptance (%) (%) Average percentage difference in mid stance (%) Applied Bionics and Biomechanics 7 Table 1: Statistical relationships between thermal and force parameters for three muscle groups: trapezius (TT), latissimus dorsi (TL), and obliquus abdominis (TO), and three ground reaction force values: maximal weight acceptance force (WA), maximal force in midstance (MS), and maximal force in push-off gait phase (PO), for the left and right leg, respectively. Significant relations (p <0:1 or p <0:05 for Spearman’s test) are written in bold. Left side Right side Load (%) Load type Force Muscle ∗ 2 ∗ 2 r or r pr description r r or r pr description r 5% Backpack MS TL -0.757 0.018 Very strong negative 0.573 0.311 0.415 Fair positive 0.097 5% Backpack MS TT -0.233 0.547 Fair negative 0.054 0.878 0.002 Very strong positive 0.771 5% Backpack PO TL -0.852 0.004 Very strong negative 0.726 0.881 0.002 Very strong positive 0.777 5% Backpack WA TO 0.691 0.039 Moderate positive 0.477 0.123 0.753 Poor positive 0.015 10% Backpack PO TL 0.351 0.354 Fair positive 0.123 -0.629 0.069 Moderate negative 0.396 10% Backpack WA TL 0.177 0.649 Poor positive 0.031 -0.805 0.009 Very strong negative 0.649 15% Backpack MS TT 0.134 0.731 Poor positive 0.018 -0.867 0.002 Very strong negative 0.752 15% Backpack WA TT 0.135 0.729 Poor positive 0.018 -0.621 0.075 Moderate negative 0.385 15% Bag across MS TO -0.707 0.033 Very strong negative 0.500 0.586 0.097 Moderate positive 0.344 15% Bag across PO TL -0.696 0.037 Moderate negative 0.485 0.130 0.739 Poor positive 0.017 15% Bag across WA TL -0.382 0.311 Fair negative 0.146 0.733 0.025 Very strong positive 0.537 15% Bag across WA TO -0.334 0.380 Fair negative 0.111 0.711 0.032 Very strong positive 0.505 5% Bag one hand PO TT 0.378 0.209 Fair positive 0.143 -0.585 0.098 Moderate negative 0.342 15% Bag one hand MS TL -0.756 <0.05 Very strong negative — 0.235 >0.05 Fair positive — 15% Bag one hand MS TT 0.031 0.937 Poor positive 0.001 -0.599 0.088 Moderate negative 0.359 15% Bag one hand PO TL -0.807 <0.05 Very strong negative — 0.521 >0.05 Moderate positive — 15% Bag one hand WA TL -0.277 >0.05 Fair negative — 0.731 <0.05 Very strong positive — 15% Bag one hand WA TT 0.636 0.066 Moderate positive 0.404 -0.026 0.947 Poor negative 0.001 5% Bag shoulder MS TO 0.792 0.011 Very strong positive 0.628 -0.385 0.306 Fair negative 0.148 15% Bag shoulder MS TL 0.586 0.097 Moderate positive 0.343 -0.240 0.534 Fair negative 0.058 15% Bag shoulder MS TO 0.329 0.387 Fair positive 0.108 -0.641 0.063 Moderate negative 0.411 15% Bag shoulder PO TO 0.673 0.047 Moderate positive 0.453 -0.259 0.501 Fair negative 0.067 15% Bag shoulder PO TT -0.373 0.322 Fair negative 0.139 0.750 0.020 Very strong positive 0.562 15% Bag shoulder WA TO 0.757 0.018 Very strong positive 0.573 -0.132 0.736 Poor negative 0.017 As expected, almost any asymmetrical load induces an midstance (MS), and maximal force in push-off gait phase (PO)). For normal distributed sets, the Pearson coefficients increase in the asymmetry of temperature distribution, and generally, it can be stated that higher asymmetrical load and coefficient of determination r are given (p =0:1). For nonnormal distributed sets, the Spearman coefficients are causes higher asymmetry in temperature distribution. The main exception to the rule is the case of the highest presented (p =0:05). load—15% of the body mass. It can be assumed that the addi- tional load influences the position of the center of mass which changes the kinematics of the body and excessive 4. Discussion physical effort causes sweating, and this influences the tem- The experiment was focused on the effects of an asymmetri- perature distribution. Similar phenomena were observed in other works [36, 37]. cal load on the work of trunk muscles and differences in ground reaction forces. In particular, the asymmetry of tem- Results reveal asymmetrical muscle work caused by their perature distribution was observed (Figures 3–5). The high- asymmetric activity and force production caused by an asym- est differences were reached for the obliquus abdominis in metric external load. A similar testing procedure to the pre- the case of 15% load carried on the shoulder (0.37 K) and sented one was done in work [38], but the technique of for the latissimus dorsi for 10% load in the case of a bag car- muscle activity recording was surface electromyography. ried in one hand (0.2 K), and it was slightly less for a bag on Results in the mentioned study pointed out statistically sig- one shoulder with 5% of the load (0.19 K). For the trapezius nificant differences only for the trapezius and erector spinae muscle, the highest asymmetry was reached for the bag car- but not statistically significant differences in latissimus dorsi ried on one shoulder with 10% of body load (10% increase). and obliquus abdominis activity. Based on those results, we can assume that a COM Results presented in this study showed such dependence (center of mass) translation and compensation of the asym- in all cases except for the cross-body bag. However, one metrical load cause a counterbalance of spine lateral flexion might try to define nonlinear relationships between thermal and lead to asymmetrical trunk muscle activation. and ground reaction force parameters, but this demands to 8 Applied Bionics and Biomechanics linear correlations is similar to those identified for the bag test a bigger number of subjects. According to the experiment carried out and presented in the paper [39], the biggest differ- carried in one hand but mostly for the left side of the body ences should be visible for the volunteer carrying a bag in the and for the obliquus abdominis muscle (see Table 1). Considering a bag carried across the body (on the right position lower than the level of the shoulder. In this study, this is not proven. For most volunteers, it may be concluded side) (the best one), one can induce that external load is sta- that the posture is not exactly symmetrical according to the bilized, and that is why this is the less fatigable position. sagittal plane and this is perfectly normal. Increased activation of contraction of the opposite trapezius Additional COM translation verification may be consid- and abdominis should be expected. ered here, e.g., by using motion capture or IMU systems [40]. The bigger number of statistically significant linear corre- The results of the experiment carried out with children’s lations was obtained for the left side and only for obliquus participation [41] prove the asymmetrical muscle activity abdominis and latissimus dorsi muscles (see Table 1). among those with the problem of scoliosis with one curve as well as double curve one. In the presented study, the tem- 5. Conclusions perature difference between right and left muscles before any activity is positive value and shows an asymmetrical muscle Obtained results show that during gait with an additional activity. Generally, the trapezius muscle is increasingly acti- load held asymmetrically, the symmetry of muscle force pro- vated with increasing external load on the right side. If the duction changes. With the increasing weight of the carried load is not distributed bilaterally, there is an increased muscle load, the differences of temperature become higher; however, activity of the superior part of the trapezius on the side that different types of loading cause different patterns of the bag is worn on. The same conclusion was found in the compensation and influence the ground reaction forces in publication [38]. In all examined cases where the additional different ways. load was distributed nonuniformly, the trapezius was more A general observation allows us to make a statement. that activated on the side where the strap was held on. This is in the case of the asymmetrical way of carrying the external probably due to the volunteers trying to maintain the proper load, the less harmful for the musculoskeletal system seems scapula and clavicle position to ensure the strap of the bag is to be the placing the strap across the torso because in this kept over the shoulder while the trunk is laterally flexed so case, the smallest increase in temperature asymmetry was that the center of mass of the body remains over the support observed. On the other hand, the worst method is to keep area during gait. the load in one hand or on the shoulder especially when we The asymmetry of GRFs is revealed in Figures 6–8. Gen- use to carry the load only one side almost every time—in this erally, the highest asymmetry is obtained for MS forces. case, the highest increase in temperature asymmetry was Based on the obtained results and those found in literature, present. we can assume that a COM translation and compensation Generally, it should be underlined that the results of the asymmetrical load present in a form of counterbalance indicate that walking with the asymmetric load inducts cause spine lateral flexion and result in asymmetrical trunk compensation made by muscles and posture and increases muscle activation. Repeating this type of asymmetrical load- the possibility of muscle injury and leads to or increases ing of the musculoskeletal system is linked with greater shear faulty posture, even if this study will be treated as a prelimi- and compressive forces present in the spine [37]. The authors nary study, limited to relatively young and fit males. of [37] pointed out also that “asymmetric lifting is more stressful than frontally symmetric lifting.” Considering the backpack load type (carried on the right Data Availability side of the body), increased activation of the right abdominis and right latissimus muscles should be expected. The bigger The thermography image data and pedobarographic force number of statistically significant linear correlations was platform data used to support the findings of this study are obtained for the right side, mostly for the trapezius and latis- available from the corresponding author upon request. simus dorsi muscles (see Table 1). Considering a bag carried in the right hand, increased activation of the right opposite trapezius, latissimus, and Conflicts of Interest abdominis should be expected. The position of external load with respect to the COM of the body is the most distant with The authors declare that there is no conflict of interest respect to the other configurations of the load, and that is regarding the publication of this paper. why one should expect that this carrying could be the most fatigable ones. To avoid fatigue, the musculoskeletal should activate different muscle groups, and that is why the lowest Acknowledgments number of statistically significant linear correlation (for trapezius and latissimus dorsi muscles) was found in this case We want to thank students Anna Frątczak, Angelika (see Table 1). Puchalska, Jarosław Chruściel, and Siam Streibl for their help Considering a bag carried on right shoulder, increased in preparation and conducting experiments. This paper was activation of the right trapezius, abdominis, and latissimus supported by the Grant for Young Scientists Lodz University should be expected. 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Applied Bionics and BiomechanicsHindawi Publishing Corporation

Published: Jul 29, 2021

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