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Influences of Different Drop Height Training on Lower Extremity Kinematics and Stiffness during Repetitive Drop Jump

Influences of Different Drop Height Training on Lower Extremity Kinematics and Stiffness during... Hindawi Applied Bionics and Biomechanics Volume 2021, Article ID 5551199, 9 pages https://doi.org/10.1155/2021/5551199 Research Article Influences of Different Drop Height Training on Lower Extremity Kinematics and Stiffness during Repetitive Drop Jump 1 1 2 2 2 2 I-Lin Wang , Yi-Ming Chen , Ke-Ke Zhang , Yu-Ge Li , Yu Su , Chou Wu , 3,4 and Chun-Sheng Ho College of Physical Education, Hubei Normal University, Huangshi 435002, China Graduate Institute, Jilin Sport University, Changchun, 130022 Jilin, China Division of Physical Medicine and Rehabilitation, Lo-Hsu Medical Foundation, Inc., Lotung Poh-Ai Hospital, Yilan 26546, Taiwan Department of Physical Therapy, College of Medical and Health Science, Asia University, Taichung 41354, Taiwan Correspondence should be addressed to Yi-Ming Chen; 1021302@ntsu.edu.tw and Chun-Sheng Ho; cochonho@gmail.com Received 22 January 2021; Revised 7 February 2021; Accepted 22 February 2021; Published 4 March 2021 Academic Editor: Donato Romano Copyright © 2021 I-Lin Wang 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. Drop jump (DJ) is often used as a plyometric exercise to improve jumping performance. Training from improper drop heights and for improper durations lead to unfavorable biomechanical changes in the lower extremities when landing, which result in reduced training effects and even lower extremity injuries. Purpose. To study the effects of repeated DJ training at drop heights of 30 cm, 40 cm, and 50 cm (drop jump height (DJH) 30, DJH40, and DJH50) on lower extremity kinematics and kinetics. The 1st, 50th, 100th, 150th, and 200th DJs (DJ1, DJs50, DJs100, DJs150, and DJs200) were recorded by using a BTS motion capture system and force platform. The MATLAB software was used to compare the kinematic and stiffness data of DJ1, DJs50, DJs100, DJs150, and DJs200 with one-way ANOVA repeated measure. If there were significant differences, the LSD method was used for post hoc comparisons. Methods. Twenty healthy male Division III athlete volunteers were selected as subjects, and 200 drop jumps (DJs200) were performed from DJH30, DJH40, and DJH50. Results. The jumping height (JH), contact time (CT), and GRF increased with drop height, and the stiffness of the legs and ankle at DJH30 was higher than that at DJH40 and DJH50 (p <0:05). Conclusion. Within DJs200, training at DJH50 yield the high impact easily leads to lower extremity injury; training at DJH30 can increase the stiffnesses of the legs and ankle joints, thus effectively utilizing the SSC benefits to store and release elastic energy, reducing the risk of lower extremity musculoskeletal injury. Therefore, coaches can choose different drop heights and training quantities for each person to better prevent lower extremity injury. extremity injury [3]. Therefore, too high of a drop height 1. Introduction leads to excessive GRFs and lower extremity injury. The pre- Plyometric exercise is a type of exercise in which the muscle activation phase characteristics in DJ training systematically is stretched directly before it is explosively contracted during change with the drop height; therefore, lower extremity the stretch-shortening cycle (SSC) to generate high levels of strength can be increased during DJ training [4]. Choosing force and power, and the DJ is often performed during plyo- the appropriate drop height during the DJ task can not only metric training [1]. DJ training with maximum vertical help improve performance by inducing the best training- jumps performed immediately from a platform can be used related physiological adaptations but also help avoid injury to improve jumping performance [2]. Eccentric contraction to the muscle tendon and bone caused by overload on the during the downward phase immediately followed by a rapid lower extremities during jumps from high heights [5, 6]. Compared to the optimal drop height, a lower drop height concentric contraction during the takeoff is needed to com- plete DJ action with the participant of the SSC. However, results in interlimb asymmetry in strength [7], and a higher an excessive landing force with decreased physiological drop height does not enable small adjustments in muscle absorption causes large knee valgus, which leads to lower activity, which can even decrease rather than increase 2 Applied Bionics and Biomechanics studies have shown that ankle stiffness decreases gradually power output [4, 8]. Therefore, the optimal drop height may need to be selected according to the jumping ability with increasing drop height, resulting in smaller SSC benefits of each participant [9]. [6]. A drop height that is too high causes the DJ to over- stretch the muscles during landing, decreasing lower extrem- In competitions, athletes jump and land multiple times to complete multiple high-intensity short-duration sprints, ity stiffness, which easily induces the neuroprotective cuts, and spins [10], and all of these movements require a inhibition process and reduces Hoffman reflex activity [24, high level of reactive strength and force-generating capabili- 25]. An appropriate level of joint stiffness can effectively trig- ties of the lower extremities [11]. High athletic performance ger the SSC mechanism to enhance the training effect, while repeated DJs induce muscle fatigue and changes in stiffness requires an adequate level of lower extremity strength [12], and DJ training yields adequate training effects [13]. Athletes and the landing strategy, which limits jumping performance usually perform plyometric jumps to improve their explosive [20]. Therefore, the stiffness of lower extremity joints is jump performance, and the DJ is the most common plyomet- affected by both drop height and training volume. The opti- ric exercise [6]. DJ training can improve muscle power by mal drop height and training volume can effectively trigger the SSC mechanism to yield an appropriate stiffness, reduce SSC mechanism, thereby enhancing athletic and vertical jumping performance [1, 14, 15]. Therefore, most athletes the risk of lower extremity injury, and enhance jumping can use strength training with repeated jumps to improve performance during repeated DJ training. the strength and biomechanical characteristics of the lower In summary, drop height and training volume affect DJ extremities. In addition, DJ training improves the ability of landing performance, and changes in these factors yield tendons and muscles to store and release elastic energy different training effects. An improper height and training within the landing phase of jumps [16], thus increasing the volume lead to lower extremity musculoskeletal injuries. In lower extremity strength and allowing individuals to jump this study, it was hypothesized that JH, CT, RSI, and GRF from higher heights. Jumping height can predict muscle increase as the drop height and training volume increase strength in the lower extremities, so various vertical jumps and that stiffness decreases as the drop height increases. With are often included in a standard test of athletic performance the optimal drop height and training volume, the SSC mech- [2]. However, repeated DJ training from different platforms anism may more effectively increase muscle spindle sensitiv- is likely to lead to neuromuscular fatigue and changes in ity, enhance endurance, improve athletic performance, and lower extremity dynamics, which can lead to injury. Landing prevent lower extremity injury during DJ training. The main strategies, including strategies of bouncing and absorbing objectives of this study were to explore the training effects of energy, affect athletic performance [17], and improvements highly repetitive DJs from DJH30, DJH40, and DJH50 on the in the stretch reflex may lead to higher takeoff speeds [18]. kinematics and stiffness of the lower extremities. The characteristics of preactivation can change with the drop height, and DJs from platforms higher than the optimal 2. Methods height do not allow the individual to effectively adjust muscle preactivation to adapt to the landing impact [4]; moreover, 2.1. Participants. The subjects involved in the study were 20 SSC fatigue after exercise leads to decreased stretch-reflex healthy male Division III athlete volunteers (age = 21:5±0:9 sensitivity and muscle injury during DJ training [19]. When years old, height = 174:6±4:7 cm, weight = 67:9±7:9 kg) repeated DJs performed with more extended lower extremi- from Jilin Sport University. None of the subjects had a history ties, the individuals induced muscle fatigue will increase of muscle or bone issues in the lower extremity or neurological ankle plantar flexion to absorb the impact forces as the disease within 2 years. The procedure and possible risks were compensation for increased knee extension and the change explained to subjects, and they signed written consent forms in landing strategy under this circumstance results in poor before the study began. The study was approved by the jumping performance [20]. A study showed that muscle per- regional ethics committee, and all subjects signed informed formance changed after DJs100 was repeated, and knee joint consent forms (JLSU-IRB2020004). extensor fatigue caused the jump height to decrease by 26 ±14% [21]. Therefore, repeated DJ training is likely to 2.2. Protocol. Before the study, the subjects performed a stan- induce lower extremity fatigue and muscle injury, and jumps dard dynamic warm-up for the major muscle groups of the from the optimal drop height and the optimal training lower limbs (running on a treadmill at a speed of 8 km/h volume for DJs can prevent the risk of poor performance for 10 minutes). During the study, the subjects wore standard and injury caused by excessive fatigue and help individuals shoes provided by the laboratory to control for differences in complete reinforcement training. the absorption characteristics of the soles of shoes. Three DJ The risk of lower extremity injury may be related to experiments (DJH30, DJH40, DJH50) were conducted in a changes in joint stiffness; excessive joint stiffness increases random order over 3 separate days, with 4 days of rest the risk of bone injury, while insufficient joint stiffness may between each dropping height experiment. Before data col- lead to joint instability and soft tissue injury [22]. DJ training lection, the subjects were required to practice the jump five from different drop heights is widely used to assess the risk of times to ensure that their hands were on their waist and their lower extremity injury [5], so drop height is a key factor feet were on the two force plates during the experiment. The affecting joint stiffness during landing. The optimal drop subjects were encouraged to jump with maximum effort height can regulate the lower extremity stiffness, leading to within the shortest ground contact time [26]. The data for the best SSC to enhance jumping performance [23]. Previous DJ1, DJs50, DJs100, DJs150, and DJs200 were recorded, Applied Bionics and Biomechanics 3 and a 10-second break was provided between jumps. The K was calculated by the following formula: joint framework for the proposed methodology is shown in Figure 1. ΔM ht joint K BW ∗ = , ð2Þ joint rad Δθ 2.3. Data Collection. Twenty-one reflective markers (19 mm joint in diameter) were attached to anatomical landmarks on the legs and pelvis to define a seven-segment rigid link model where the change in joint moment between the instant of of the lower extremities, according to the Helen Hayes peak joint flexion and ground contact is defined as ΔM joint marker set [27]. The three-dimensional (3D) trajectories of and the angular displacement between the maximum joint the reflective markers on the participants were collected with flexion and the contact position is Δθ . joint 10 cameras (BTS DX400, BTS Bioengineering, Milano, Italy) at a sampling frequency of 200 Hz. Two force plates (40 ∗ 60 2.5. Statistical Analysis. The MATLAB software (R2016a; cm) were used to collect GRF data during each trial at a sam- MathWorks, Inc., Natick, MA) was used for various statisti- pling frequency of 400 Hz (BTS P6000, BTS Bioengineering, cal analysis. The variables were analyzed using one-way Milano, Italy). The infrared camera data were synchronized ANOVA repeated measure for DJH30, DJH40 and DJH50 with the force plate data via the Qualisys 64 channel A/D at DJ1, DJs50, DJs100, DJs150, and DJs200. When significant plate. results were found, post hoc analysis was performed with LSD (p <0:05) pairwise comparisons to compare the mea- 2.4. Data Analysis. A kinematic model was generated by sured values between different drop heights. The effect size defining the skeletal segments (foot, talus, shank, thigh of (ES) is used to determine whether a difference is a practical both extremities, and pelvis) in the standing trial. The central correlation difference. The modified Cohen scale was used position of the hip joint was calculated by the method pro- to determine the size of variation differences in three drop posed by Bell et al. [28]. The center of the ankle joint was height, <0.2 means trivial difference, 0.2-0.6 means small dif- defined as the midpoint between the medial and lateral ference, 0.6-1.2 means moderate difference, and 1.2-2.0 malleolus. The midpoint between the medial and lateral epi- means large difference [29]. condyles was defined as the knee joint center. The anatomic coordinate systems of the thigh and shank were determined 3. Results by the static calibration test. The vertical axis was defined as the line from the distal to proximal centers of the joint, Figure 2 presents the mean deviations of each dependent while the anteroposterior axis was perpendicular to the verti- kinematic variable of the lower extremities. Jumping height cal axis; the third axis was defined as the cross product of the and contact time increased significantly overall (all p < anteroposterior and vertical axes and used to obtain the 0:005) across the three increasing drop heights, and post dynamic coordinate systems of the pelvis, thigh, and shank. hoc analysis revealed significant differences between We performed all calculations using a custom MATLAB DJH30, DJH40, and DJH50. Our results show that jumping program (Mathworks, Natick, RI, USA). height was 1.05-, 1.08-, 1.04-, 1.07-, and 1.08-fold higher The landing phase was defined as the time interval from (all p <0:048; ES varying from 0.48 to 0.73) during DJH40 when the foot contacted the ground to the lowest center-of- than DJH30; 1.13-, 1.15-, 1.07-, 1.13-, and 1.16-fold higher mass position. A fourth-order low-pass Butterworth digital (all p <0:006; ES varying from 0.71 to 1.35) during DJH50 filter with a cutoff frequency of 50 Hz was used to smooth than DJH30; and 1.07-, 1.07-, 1.04-, 1.06-, and 1.07-fold the GRF data. Jumping height (JH) was calculated by the fol- higher (all p <0:046; ES varying from 0.48 to 0.67) during lowing formula: JH = gT /8. Contact time (CT) was defined DJH50 than DJH40 at DJ1, DJs50, DJs100, DJs150, and as the time from initial ground contact to toe-off during the DJs200, respectively (Figure 2(a)). The post hoc comparisons foot ground contact phase. The reaction strength index showed that contact time was 1.08-, 1.08-, 1.09-, 1.08-, and (RSI) was calculated as follows: RSI = JH/CT. The peak 1.07-fold higher (all p <0:049; ES varying from 0.47 to vertical ground reaction force (PVGRF) was defined as the 0.68) during DJH40 than DJH30; was 1.19-, 1.23-, 1.24-, maximum PVGRF at the initial point of contact with the 1.23-, and 1.18-fold higher (all p <0:002; ES varying from ground to the maximum angle of knee flexion. The PGRF 0.85 to 1.57) during DJH50 than DJH30; and 1.10-, 1.13-, was normalized by the subjects’ body weight (BW). 1.13-, 1.14-, and 1.11-fold higher (all p <0:041; ES varying K was calculated using the following formula: leg from 0.49 to 0.82) during DJH50 than DJH40 at DJ1, DJs50, DJs100, DJs150, and DJs200, respectively (Figure 2(b)). The reaction strength index value during vertical GRF ht hip−lowest DJH50 was significantly higher than DJH30 and DJH40 K BW ∗ = , ð1Þ leg rad ΔL leg (p <0:050), and the post hoc comparisons showed that dur- ing DJH50 was 1.14-fold (p =0:048; ES = 0:47) higher than DJH30 and 1.14-fold (p =0:021; ES = 0:56) higher than where the vertical GRF at the lowest position of the hip joint DJH40 at DJ1. The reaction strength index value during is the vertical GRF and ΔL represents the vertical DJH40 was significantly higher than DJH30 and DJH50 (all hip−lowest leg displacement of the hip from the contact position to the p <0:050), and the post hoc comparisons showed that the lowest position [26]. values were 1.08-, 1.06-, 1.12-, and 1.17-fold higher (all 4 Applied Bionics and Biomechanics Running on a treadmill at a speed Warm up of 8km/h for 10 minutes Markers attach Jumping with the maximum effort Five DJs for practice in the shortest ground contact time DJs200 from DJH30 cm R andomization DJ1, DJs50, DJs100, DJs150 and DJs200 from DJH40 cm DJs200 for data analysis DJs200 from DJH50 cm Figure 1: Framework for the proposed methodology. p <0:028; ES varying from 0.54 to 0.74) during DJH40 than decreased significantly overall (all p <0:050) across the three DJH30 and were 10.26%, 13.94%, 14.87%, and 13.14% lower increasing drop heights, with the post hoc results showing during DJH50 than DJH40 (all p <0:029; ES varying from differences between DJH30, DJH40, and DJH50. The post 0.53 to 0.70) at DJs50, DJs100, DJs150, and DJs200, respec- hoc comparisons showed that the leg stiffness was lower dur- tively (Figure 2(c)). ing DJH40 than DJH30, with ∇ values of 10.46%, 15.43%, Figure 2 presents the mean deviations of each dependent 17.62%, 12.38%, and 7.53% (all p <0:047; ES varying from ground reaction force variable for the lower extremities. The 0.48 to 0.64) and lower during DJH50 than DJH30, with ∇ peak ground reaction force and leg ground reaction force sig- values of 20.97%, 30.05%, 32.03%, 25.06%, and 23.82% (all nificantly increased overall (all p <0:050) across the three p <0:030; ES varying from 0.53 to 0.87) at DJ1, DJs50, increasing drop heights, with the post hoc results showing DJs100, DJs150, and DJs200, respectively; the values were differences between DJH30, DJH40, and DJH50. The post lower during DJH50 than DJH40, with ∇ values of 17.28%, hoc comparisons showed that peak ground reaction force 18.31%, 14.47%, and 17.62% (all p <0:043; ES varying from was 1.05-, 1.05-, and 1.07-fold higher (all p <0:018; ES vary- 0.49 to 0.58) at DJs50, DJs100, DJs150, and DJs200, respec- ing from 0.59 to 0.84) during DJH40 than DJH30 at DJs100, tively (Figure 3(a)). The post hoc comparisons showed that DJs150, and DJs200, respectively; 1.20-, 1.18-, 1.20-, 1.17-, ankle stiffness during DJH40 was lower than DJH30, with ∇ and 1.21-fold higher (all p <0:001; ES varying from 1.03 to values of 19.35%, 32.00%, 25.00%, 19.30%, and 19.09% (all 2.23) during DJH50 than DJH30; and 1.19-, 1.15-, 1.14-, p <0:040; ES varying from 0.18 to 0.91) and lower during 1.11-, and 1.13-fold higher (all p <0:001; ES varying from DJH50 than DJH30, with ∇ values of 25.81%, 30.40%, 0.91 to 1.82) during DJH50 than DJH40 at DJ1, DJs50, 37.88%, 23.68%, and 30.00% (all p <0:019; ES varying from DJs100, DJs150, and DJs200, respectively (Figure 2(e)). The 0.22 to 0.78) at DJ1, DJs50, DJs100, DJs150, and DJs200, post hoc comparisons showed that the right leg ground reac- respectively (Figure 3(d)). There were no significant differ- tion force was 1.11-, 1.05-, and 1.06-fold higher (all p <0:022; ences in knee or hip stiffness between DJH30, DJH40, and ES varying from 0.56 to 0.86) during DJH40 than DJH30 at DJH50 (Figures 3(b) and 3(c)). DJs100, DJs150, and DJs200, respectively; 1.17-, 1.21-, 1.23-, 1.16-, and 1.18-fold higher (all p <0:002; ES varying from 0.87 to 1.25) during DJH50 than DJH30; and 1.24-, 1.15 4. Discussion 1.11-, 1.11-, and 1.11-fold higher (all p <0:008; ES varying from 0.67 to 1.77) during DJH50 than DJH40 at DJ1, The purposes of this study were to investigate the effects of DJs50, DJs100, DJs150, and DJs200, respectively highly repetitive DJs from DJH30, DJH40, and DJH50 on (Figure 2(d)). The post hoc comparisons showed that the left lower extremity kinematics and stiffness and to determine leg ground reaction force was 1.15-, 1.13-, 1.14-, 1.14-, and the appropriate drop height and training volume of drop 1.15-fold higher (all p <0:050; ES varying from 0.56 to jump training. The results show that jumping height and 1.04) during DJH50 than DJH30 at DJ1, DJs50, DJs100, contact time reached the maximum values within DJs200 at DJs150, and DJs200, respectively, and 1.08-, 1.10-, and DJH50, and training at this height and volume can improve 1.11-fold (all p <0:005; ES varying from 0.72 to 0.81) higher jumping performance; however, the large ground reaction than during DJH40 at DJs100, DJs150, and DJs200, respec- force generates a high impact force, which can easily lead to tively (Figure 2(f)). lower extremity injury. Leg and ankle stiffness are maximal Figure 3 presents the mean deviations of each dependent at DJH30, which can reduce the risk of lower extremity mus- lower extremity stiffness variable. The leg and ankle stiffness culoskeletal injury and effectively utilize stretch-shortening Applied Bionics and Biomechanics 5 DJs100 DJs100 42 †‡ †‡ † DJs150 DJs150 0.4 † †‡ †‡ DJs50 †‡ DJs50 †‡ † 0.2 † 0 0.0 DJs200 DJs200 –14 †‡ –0.2 †‡ †‡ †‡ –28 DJ1 DJ1 –0.4 –42 (a) (b) DJs100 DJs100 †‡ 1.8 DJs150 DJs150 1.2 24 DJs50 † DJs50 †‡ †‡ 0.6 0.0 –12 DJs200 –0.6 DJs200 †‡ †‡ †‡ –24 –1.2 DJ1 DJ1 –36 –1.8 –48 (c) (d) DJs100 DJs100 †‡ †‡ DJs150 DJs150 1.2 †‡ †‡ † DJs50 †‡ DJs50 0.6 0 0.0 –1 DJs200 DJs200 –0.6 †‡ † †‡ †‡ –2 DJ1 DJ1 –1.2 –3 DJH30 DJH40 DJH50 (e) (f) Figure 2: The jumping height, contact time, reaction strength index, the peak vertical GRF, and right and left leg GRF during drop jumps from three heights at DJ1, DJs50, DJs100, DJs150, and DJs200. Asterisk † indicates that a significant difference with DJH30; ‡ indicates that a significant difference with DJH40; § indicates that a significant difference with DJH50. p values <0.05 were considered to significantly differ. cycle benefits to store and release elastic energy to improve can follow the natural trend of the substrate recoil, thus wast- jumping performance. ing a minimum amount of energy [32]. In this study, jump- In this study, within DJs200, jumping height and contact ing height increased gradually with drop height, which may time gradually increased with increasing drop height. Previ- have been caused by the jumping ability increasing with ous studies have shown that jumping height and contact time increasing contact time. Therefore, the DJH50 height had a increase with increasing drop height [6, 30] and that the longer contact time than did different jumps and exhibited training intensity can be enhanced and the values of jump a jumping height increase, which may have produced a better parameters such as jumping height and contact time can be training effect. In this study, reaction strength index was influenced by the drop height [6]. However, some studies higher during DJH50 than during DJH30 and DJH40 at have shown that jumping height decreases with drop height DJ1, while when landing, the reaction strength index was [6]. Increased contact time results in increased knee flexion higher during DJH40, than during DJH30 and DJH50 at to absorb the increased landing force and thus greater jump- DJs50, DJs100, DJs150, and DJs200. The differences in reac- ing ability [7, 31]. And the long contact time with the ground tion strength index according to the drop height and jump Jumping height (cm) PGRF (BW) RSI (cm/s) LGRF (BW) RGRF (BW) Contact time (s) 6 Applied Bionics and Biomechanics DJs100 DJs100 0.08 DJs150 ‡ 0.06 DJs150 3.2 DJs50 0.04 DJs50 1.6 0.02 0.0 0.0 –0.02 DJs200 DJs200 –1.6 –0.04 DJ1 DJ1 –3.2 –0.06 –0.08 (a) (b) DJs100 DJs100 0.15 0.2 DJs150 DJs150 0.10 DJs50 DJs50 0.1 0.05 0.0 0.00 DJs200 DJs200 –0.05 –0.1 DJ1 DJ1 –0.10 –0.2 –0.15 DJH30 DJH40 DJH50 (c) (d) Figure 3: The right leg, hip, knee, and ankle stiffness during drop jumps from three heights at DJ1, DJs50, DJs100, DJs150, and DJs200. Asterisk † indicates that a significant difference with DJH30; ‡ indicates that a significant difference with DJH40; § indicates that a significant difference with DJH50. p values <0.05 were considered to significantly differ. time are due to the changes in jumping height and contact findings, our results show that the resistance training inten- time. The higher the jumping height and the shorter the con- sity can be controlled by the drop height, resulting in the ground reaction force gradually increasing with increasing tact time are, the higher the reaction strength index [33, 34]. Too high of a drop height altitude will produce a large land- drop height [35]. High drop heights cause individuals to land ing impact and is not conducive to muscle fine-tuning which during DJs with high impact intensity [6], which can lead to can even decrease rather than increase power output; after ankle sprains, anterior cruciate ligament tears, and patellofe- repeated DJs, muscle fatigue will lead to a smaller stretch- moral pain syndrome [36]. Therefore, landing with high shortening cycle benefit and reaction strength index differ- impact during DJH50 can cause lower extremity injury and ence at different drop heights [4, 8, 19]. Thus, the gradual is not suitable for repeated contact time training. There were increase in drop height may lead to a change in the reaction significant differences in ground reaction force between strength index difference when the DJH40 and DJH50 jump DJH30 and DJH40 at DJs100, DJs150, and DJs200. These dif- times are different. This study showed that after DJ1, the ferences may have been caused by the differences in the initial DJH40 height produces a larger reaction strength index, peak vertical ground reaction force at ground contact due to which can have a larger training effect, while after repeat fatigue and individual changes in joint stiffness [17, 37]. drop jump training at the DJH50 height, muscle fatigue Therefore, the impact force can be changed by controlling may decrease the stretch-shortening cycle benefit, resulting the training intensity at different drop heights. In this study, in a decrease in the reaction strength index. Therefore, drop smaller ground reaction forces reduced the risk of lower heights of DJH40 and DJH50 can produce greater reaction extremity musculoskeletal injury when landing at DJ1, strength index values, and the reaction strength index value DJs50, DJs100, DJs150, and DJs200 from the height of may be more suitable for drop jump training; however, train- DJH30. In this study, during landing from DJH40 and DJH50 ing from DJH50 for 200 consecutive times produces a lower reaction strength index, which may easily cause muscle within DJs200, the stiffnesses of the legs and ankle joints were fatigue and poor jumping performance. lower than those during landing from DJH30, while there The results of this study show that the ground reaction were no differences in the stiffnesses of the knees and hips force produced at DJH50 within DJs200 is greater than those between other drop heights. Consistent with previous find- ings, the stiffnesses of the legs and ankle gradually decreased produced at DJH30 and DJH40. Consistent with previous Hip stiffness(BW ht/rad) Leg stiffness(BW ht/rad) ⁎ ⁎ Ankle stiffness(BW ht/rad) Knee stiffness(BW ht/rad) Applied Bionics and Biomechanics 7 and stiffness by the drop height will affect the stability of with increasing drop height, while the stiffnesses of the knees and hips did not significantly differ across drop heights [6, the knee joint. Within DJs200, training at the height of 26, 38]. The ankle stiffness decreased gradually with increas- DJH50 can yield better jumping performance; however, ing drop height, resulting in a decrease in the stretch- because the high impact easily leads to lower extremity shortening cycle benefit when drop jump training [6]; there- injury, training at the drop height of DJH30 can increase fore, the smaller ankle stiffness may have affected the training the stiffnesses of the legs and ankle joints, thus effectively uti- effect. Increasing stiffness enables better storage and release lizing the SSC benefits to store and release elastic energy, of stretch-shortening cycle-based elastic energy [38]. In addi- improving jumping performance and reducing the risk of tion, jumping training can increase the joint stiffness of the lower extremity musculoskeletal injury. lower extremities during landing, reduce the risk of injury, and improve athletic performance by strengthening the Abbreviations lower extremity muscles [39]. The higher leg and ankle stiff- DJ: Drop jump nesses generated by highly repetitive drop jump training at DJH: Drop jump height DJH30 in this study can lead to greater stretch-shortening JH: Jumping height cycle benefits regarding the storage and release of elastic CT: Contact time energy and reduce the incidence of lower extremity injuries, SSC: Stretch-shortening cycle which may be suitable for repetitive drop jump training. Past RSI: Reaction strength index studies have shown that the longer the contact time at drop BWs: Body weights jump landing is, the lower the stiffness of the lower extremi- ES: Effective size ties [40]. In this study, contact time increased gradually with GRF: Ground reaction force increasing drop height, so the stiffnesses of the legs and ankle PGRF: Peak ground reaction force may be related to the increase in contact time. Therefore, if RGRF: Right leg ground reaction force athletes can consciously control the contact time during LGRF: Left leg ground reaction force training, they may adjust the lower extremity stiffnesses at PVGRF: Peak vertical ground reaction force. landing according to the drop height. The stiffnesses of lower extremity joints are affected by joint torques. In this study, the knee and hip stiffnesses showed no differences after Data Availability repeated drop jump training, which may have occurred The data results are included in the manuscript. because the knee and hip torques did not change significantly between the drop heights. In summary, drop jump training Conflicts of Interest with the appropriate lower extremity stiffness or stiffness adjustments during repeated jumping training can reduce All authors declare that they have no conflicts of interest with the risk of lower extremity injury and enhance the training regard to the contents of this article. effect. This study showed that landing from the DJH30 height within DJs200 produces larger leg and ankle stiffnesses, Authors’ Contributions which can yield greater stretch-shortening cycle benefits, thereby improving jumping performance and reducing the YMC and ILW designed the experiments. YMC, ILW, and risk of lower extremity injury, so these parameters are YSC carried out the supplement preparation and laboratory suitable for repeated drop jump training. experiments. ILW, WCC, and YMC analyzed the data, inter- preted the results, prepared the figures, and wrote the 4.1. Limitations. Limitations need to be considered when manuscript. WCC, SZ, and YMC contributed the reagents, interpreting the results. Firstly, amounts of drop height are materials, and the analysis platforms. not sufficient, so we need lower and higher DJH such as 20 cm and 60 cm. Secondly, the subjects were obviously not Acknowledgments blinded to the DJH, so the central nervous system may apply a protective strategy, and this could introduce performance The authors would like to thank all colleagues and students bias. Thirdly, electromyographic was not used in this study, who contributed to this study. This work was supported by so the activity of the lower limb muscles is unknown during the Research on Hubei province education department landing and jumping. science and technology research program (grant number D20202502). This manuscript was edited by American Jour- 5. Conclusion nal Experts Editing. In summary, with increasing drop height, the kinematics and References stiffnesses of the lower extremities varied during landing. DJ training from a high drop height produces a high impact [1] M. Walsh, A. Arampatzis, F. Schade, and G. P. Brüggemann, intensity, resulting in a greater impact. Compared with the “The effect of drop jump starting height and contact time on heights of DJH30 and DJH40, the DJH50 height yielded power, work performed, and moment of force,” Journal of higher JH, CT, and GRF values, as well as smaller leg and Strength and Conditioning Research, vol. 18, no. 3, pp. 561– ankle stiffnesses during landing; the changes in kinematics 566, 2004. 8 Applied Bionics and Biomechanics [18] P. V. Komi and A. Gollhofer, “Stretch reflexes can have an [2] D. Matavulj, M. Kukolj, D. Ugarkovic, J. Tihanyi, and S. Jaric, “Effects of pylometric training on jumping performance in important role in force enhancement during SSC exercise,” junior basketball players,” Journal of sports medicine and phys- Journal of applied biomechanics, vol. 13, no. 4, pp. 451–460, ical fitness, vol. 41, no. 2, pp. 159–164, 2001. 1997. [3] K. J. Simpson and L. Kanter, “Jump distance of dance landings [19] T. Horita, P. Komi, I. Hämäläinen, and J. Avela, “Exhausting influencing internal joint forces: I. Axial forces,” Medicine and stretch-shortening cycle (SSC) exercise causes greater impair- science in sports and Exercise, vol. 29, no. 7, pp. 916–927, 1997. ment in SSC performance than in pure concentric perfor- mance,” European Journal of Applied Physiology, vol. 88, [4] V. Mrdakovic, D. B. Ilic, N. Jankovic, Z. Rajkovic, and no. 6, pp. 527–534, 2003. D. Stefanovic, “Pre-activity modulation of lower extremity muscles within different types and heights of deep jump,” Jour- [20] J. T. Weinhandl, J. D. Smith, and E. L. Dugan, “The effects of nal of sports science and medicine, vol. 7, no. 2, p. 269, 2008. repetitive drop jumps on impact phase joint kinematics and kinetics,” Journal of Applied Biomechanics, vol. 27, no. 2, [5] H.-T. Peng, T. W. Kernozek, and C. Y. Song, “Quadricep and pp. 108–115, 2011. hamstring activation during drop jumps with changes in drop height,” Physical Therapy in Sport, vol. 12, no. 3, pp. 127–132, [21] K. Kubo, H. Kanehisa, and T. Fukunaga, “Influences of repet- 2011. itive drop jump and isometric leg press exercises on tendon properties in knee extensors,” Journal of strength and condi- [6] H.-T. Peng, “Changes in biomechanical properties during tioning research, vol. 19, no. 4, pp. 864–870, 2005. drop jumps of incremental height,” Journal of Strength and Conditioning Research, vol. 25, no. 9, pp. 2510–2518, 2011. [22] R. J. Butler, H. P. Crowell III, and I. M. C. Davis, “Lower extremity stiffness: implications for performance and injury,” [7] N. B. Ball, C. G. Stock, and J. C. Scurr, “Bilateral contact Clinical biomechanics, vol. 18, no. 6, pp. 511–517, 2003. ground reaction forces and contact times during plyometric drop jumping,” Journal of Strength and Conditioning Research, [23] P. J. Byrne, K. Moran, P. Rankin, and S. Kinsella, “A compar- vol. 24, no. 10, pp. 2762–2769, 2010. ison of methods used to identify ‘Optimal’ Drop height for early phase adaptations in depth jump training,” Journal of [8] M. Ruan and L. Li, “Influence of a horizontal approach on the Strength and Conditioning Research, vol. 24, no. 8, pp. 2050– mechanical output during drop jumps,” Research quarterly for 2055, 2010. exercise and sport, vol. 79, no. 1, pp. 1–9, 2008. [24] N. J. Chimera, K. A. Swanik, C. B. Swanik, and S. J. Straub, [9] M. S. Matic, N. R. Pazin, V. D. Mrdakovic, N. N. Jankovic, “Effects of plyometric training on muscle-activation strategies D. B. Ilic, and D. L. J. Stefanovic, “Optimum drop height for and performance in female athletes,” Journal of athletic train- maximizing power output in drop jump: the effect of maximal ing, vol. 39, no. 1, pp. 24–31, 2004. muscle strength,” Journal of Strength and Conditioning Research, vol. 29, no. 12, pp. 3300–3310, 2015. [25] W. Taube, C. Leukel, B. Lauber, and A. Gollhofer, “The drop height determines neuromuscular adaptations and changes [10] S. McInnes, J. S. Carlson, C. J. Jones, and M. J. McKenna, “The in jump performance in stretch-shortening cycle training,” physiological load imposed on basketball players during com- Scandinavian journal of Medicine and Science in Sports, petition,” Journal of Sports Sciences, vol. 13, no. 5, pp. 387–397, vol. 22, no. 5, pp. 671–683, 2012. [26] I.-L. Wang, S. Y. Wang, and L. I. Wang, “Sex differences in [11] C. Thomas, I. Kyriakidou, T. Dos’Santos, and P. A. J. S. Jones, lower extremity stiffness and kinematics alterations during “Differences in vertical jump force-time characteristics double-legged drop landings with changes in drop height,” between stronger and weaker adolescent basketball players,” Sports biomechanics, vol. 14, no. 4, pp. 404–412, 2015. Sports, vol. 5, no. 3, p. 63, 2017. [12] U. Alemdaroğlu, “The relationship between muscle strength, [27] I.-L. Wang et al., “Nanobubbles water curcumin extract reduces injury risks on drop jumps in women: a pilot study,” anaerobic performance, agility, sprint ability and vertical jump performance in professional basketball players,” Journal of Evidence-Based Complementary and Alternative Medicine, vol. 2019, Article ID 8647587, 9 pages, 2019. human kinetics, vol. 31, no. 1, pp. 149–158, 2012. [13] M. F. Bobbert, “Drop jumping as a training method for jump- [28] A. L. Bell, D. R. Pedersen, and R. A. Brand, “A comparison of the accuracy of several hip center location prediction ing ability,” Sports medicine, vol. 9, no. 1, pp. 7–22, 1990. methods,” Journal of biomechanics, vol. 23, no. 6, pp. 617– [14] W. R. Holcomb, J. E. Lander, R. M. Rutland, and G. D. Wilson, 621, 1990. “The effectiveness of a modified plyometric program on power and the vertical jump,” Journal of Strength and Conditioning [29] W. G. Hopkins, S. W. Marshall, A. M. Batterham, and Research, vol. 10, no. 2, pp. 89–92, 1996. J. Hanin, “Progressive statistics for studies in sports medicine and exercise science,” Medicine and Science in Sports and Exer- [15] G. J. Wilson, R. U. Newton, A. J. Murphy, and B. J. Humphries, cise, vol. 41, no. 1, pp. 3–13, 2009. “The optimal training load for the development of dynamic [30] H.-T. Peng, C. T. Khuat, T. W. Kernozek, B. J. Wallace, S. L. athletic performance,” Medicine and Science in Sports and Exercise, vol. 25, no. 11, pp. 1279–1286, 1993. Lo, and C. Y. Song, “Optimum drop jump height in division III athletes: under 75% of vertical jump height,” International [16] M. F. Bobbert, P. A. Huijing, and G. J. van Ingen Schenau, journal of sports medicine, vol. 38, no. 11, pp. 842–846, 2017. “Drop jumping. I. The influence of jumping technique on the [31] W. J. Markwick, S. P. Bird, J. J. Tufano, L. B. Seitz, and G. G. biomechanics of jumping,” Medicine and Science in Sports and Exercise, vol. 19, no. 4, pp. 332–338, 1987. Haff, “The intraday reliability of the reactive strength index calculated from a drop jump in professional men’s basketball,” [17] T. Horita, P. Komi, C. Nicol, and H. Kyröläinen, “Interaction International Journal of Sports Physiology and Performance, between pre-landing activities and stiffness regulation of the vol. 10, no. 4, pp. 482–488, 2015. knee joint musculoskeletal system in the drop jump: implica- tions to performance,” European journal of applied physiology, [32] X. Mo, D. Romano, M. Miraglia, W. Ge, and C. Stefanini, vol. 88, no. 1-2, pp. 76–84, 2002. “Effect of substrates' compliance on the jumping mechanism Applied Bionics and Biomechanics 9 of Locusta migratoria,” Frontiers in bioengineering and bio- technology, vol. 8, p. 661, 2020. [33] K. Beattie, B. P. Carson, M. Lyons, and I. C. Kenny, “The rela- tionship between maximal strength and reactive strength,” International Journal of Sports Physiology and Performance, vol. 12, no. 4, pp. 548–553, 2017. [34] C. Feldmann, L. W. Weiss, L. C. Ferreira, B. K. Schilling, and K. G. Hammond, “Reactive strength index and ground contact time: reliability, precision, and association with drop vertical jump displacement,” Journal of Strength and Conditioning Research, vol. 25, p. S1, 2011. [35] H. Makaruk and T. Sacewicz, “The effect of drop height and body mass on drop jump intensity,” Biology of Sport, vol. 28, no. 1, pp. 63–67, 2011. [36] B. D. Beynnon, P. M. Vacek, D. Murphy, D. Alosa, and D. Paller, “First-time inversion ankle ligament trauma: the effects of sex, level of competition, and sport on the incidence of injury,” The American journal of sports medicine, vol. 33, no. 10, pp. 1485–1491, 2005. [37] C. Nicol, P. Komi, and P. Marconnet, “Fatigue effects of mar- athon running on neuromuscular performance: I. Changes in muscle force and stiffness characteristics,” Scandinavian Jour- nal of Medicine and Science in Sports, vol. 1, no. 1, pp. 10–17, [38] L. Wang and H. T. Peng, “Biomechanical comparisons of single-and double-legged drop jumps with changes in drop height,” International Journal of Sports Medicine, vol. 35, no. 6, pp. 522–527, 2014. [39] M. J. Barr and V. W. Nolte, “The importance of maximal leg strength for female athletes when performing drop jumps,” Journal of Strength and Conditioning Research, vol. 28, no. 2, pp. 373–380, 2014. [40] A. Arampatzis, F. Schade, M. Walsh, and G. P. Brüggemann, “Influence of leg stiffness and its effect on myodynamic jump- ing performance,” Journal of electromyography and kinesiol- ogy, vol. 11, no. 5, pp. 355–364, 2001. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Applied Bionics and Biomechanics Hindawi Publishing Corporation

Influences of Different Drop Height Training on Lower Extremity Kinematics and Stiffness during Repetitive Drop Jump

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Hindawi Applied Bionics and Biomechanics Volume 2021, Article ID 5551199, 9 pages https://doi.org/10.1155/2021/5551199 Research Article Influences of Different Drop Height Training on Lower Extremity Kinematics and Stiffness during Repetitive Drop Jump 1 1 2 2 2 2 I-Lin Wang , Yi-Ming Chen , Ke-Ke Zhang , Yu-Ge Li , Yu Su , Chou Wu , 3,4 and Chun-Sheng Ho College of Physical Education, Hubei Normal University, Huangshi 435002, China Graduate Institute, Jilin Sport University, Changchun, 130022 Jilin, China Division of Physical Medicine and Rehabilitation, Lo-Hsu Medical Foundation, Inc., Lotung Poh-Ai Hospital, Yilan 26546, Taiwan Department of Physical Therapy, College of Medical and Health Science, Asia University, Taichung 41354, Taiwan Correspondence should be addressed to Yi-Ming Chen; 1021302@ntsu.edu.tw and Chun-Sheng Ho; cochonho@gmail.com Received 22 January 2021; Revised 7 February 2021; Accepted 22 February 2021; Published 4 March 2021 Academic Editor: Donato Romano Copyright © 2021 I-Lin Wang 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. Drop jump (DJ) is often used as a plyometric exercise to improve jumping performance. Training from improper drop heights and for improper durations lead to unfavorable biomechanical changes in the lower extremities when landing, which result in reduced training effects and even lower extremity injuries. Purpose. To study the effects of repeated DJ training at drop heights of 30 cm, 40 cm, and 50 cm (drop jump height (DJH) 30, DJH40, and DJH50) on lower extremity kinematics and kinetics. The 1st, 50th, 100th, 150th, and 200th DJs (DJ1, DJs50, DJs100, DJs150, and DJs200) were recorded by using a BTS motion capture system and force platform. The MATLAB software was used to compare the kinematic and stiffness data of DJ1, DJs50, DJs100, DJs150, and DJs200 with one-way ANOVA repeated measure. If there were significant differences, the LSD method was used for post hoc comparisons. Methods. Twenty healthy male Division III athlete volunteers were selected as subjects, and 200 drop jumps (DJs200) were performed from DJH30, DJH40, and DJH50. Results. The jumping height (JH), contact time (CT), and GRF increased with drop height, and the stiffness of the legs and ankle at DJH30 was higher than that at DJH40 and DJH50 (p <0:05). Conclusion. Within DJs200, training at DJH50 yield the high impact easily leads to lower extremity injury; training at DJH30 can increase the stiffnesses of the legs and ankle joints, thus effectively utilizing the SSC benefits to store and release elastic energy, reducing the risk of lower extremity musculoskeletal injury. Therefore, coaches can choose different drop heights and training quantities for each person to better prevent lower extremity injury. extremity injury [3]. Therefore, too high of a drop height 1. Introduction leads to excessive GRFs and lower extremity injury. The pre- Plyometric exercise is a type of exercise in which the muscle activation phase characteristics in DJ training systematically is stretched directly before it is explosively contracted during change with the drop height; therefore, lower extremity the stretch-shortening cycle (SSC) to generate high levels of strength can be increased during DJ training [4]. Choosing force and power, and the DJ is often performed during plyo- the appropriate drop height during the DJ task can not only metric training [1]. DJ training with maximum vertical help improve performance by inducing the best training- jumps performed immediately from a platform can be used related physiological adaptations but also help avoid injury to improve jumping performance [2]. Eccentric contraction to the muscle tendon and bone caused by overload on the during the downward phase immediately followed by a rapid lower extremities during jumps from high heights [5, 6]. Compared to the optimal drop height, a lower drop height concentric contraction during the takeoff is needed to com- plete DJ action with the participant of the SSC. However, results in interlimb asymmetry in strength [7], and a higher an excessive landing force with decreased physiological drop height does not enable small adjustments in muscle absorption causes large knee valgus, which leads to lower activity, which can even decrease rather than increase 2 Applied Bionics and Biomechanics studies have shown that ankle stiffness decreases gradually power output [4, 8]. Therefore, the optimal drop height may need to be selected according to the jumping ability with increasing drop height, resulting in smaller SSC benefits of each participant [9]. [6]. A drop height that is too high causes the DJ to over- stretch the muscles during landing, decreasing lower extrem- In competitions, athletes jump and land multiple times to complete multiple high-intensity short-duration sprints, ity stiffness, which easily induces the neuroprotective cuts, and spins [10], and all of these movements require a inhibition process and reduces Hoffman reflex activity [24, high level of reactive strength and force-generating capabili- 25]. An appropriate level of joint stiffness can effectively trig- ties of the lower extremities [11]. High athletic performance ger the SSC mechanism to enhance the training effect, while repeated DJs induce muscle fatigue and changes in stiffness requires an adequate level of lower extremity strength [12], and DJ training yields adequate training effects [13]. Athletes and the landing strategy, which limits jumping performance usually perform plyometric jumps to improve their explosive [20]. Therefore, the stiffness of lower extremity joints is jump performance, and the DJ is the most common plyomet- affected by both drop height and training volume. The opti- ric exercise [6]. DJ training can improve muscle power by mal drop height and training volume can effectively trigger the SSC mechanism to yield an appropriate stiffness, reduce SSC mechanism, thereby enhancing athletic and vertical jumping performance [1, 14, 15]. Therefore, most athletes the risk of lower extremity injury, and enhance jumping can use strength training with repeated jumps to improve performance during repeated DJ training. the strength and biomechanical characteristics of the lower In summary, drop height and training volume affect DJ extremities. In addition, DJ training improves the ability of landing performance, and changes in these factors yield tendons and muscles to store and release elastic energy different training effects. An improper height and training within the landing phase of jumps [16], thus increasing the volume lead to lower extremity musculoskeletal injuries. In lower extremity strength and allowing individuals to jump this study, it was hypothesized that JH, CT, RSI, and GRF from higher heights. Jumping height can predict muscle increase as the drop height and training volume increase strength in the lower extremities, so various vertical jumps and that stiffness decreases as the drop height increases. With are often included in a standard test of athletic performance the optimal drop height and training volume, the SSC mech- [2]. However, repeated DJ training from different platforms anism may more effectively increase muscle spindle sensitiv- is likely to lead to neuromuscular fatigue and changes in ity, enhance endurance, improve athletic performance, and lower extremity dynamics, which can lead to injury. Landing prevent lower extremity injury during DJ training. The main strategies, including strategies of bouncing and absorbing objectives of this study were to explore the training effects of energy, affect athletic performance [17], and improvements highly repetitive DJs from DJH30, DJH40, and DJH50 on the in the stretch reflex may lead to higher takeoff speeds [18]. kinematics and stiffness of the lower extremities. The characteristics of preactivation can change with the drop height, and DJs from platforms higher than the optimal 2. Methods height do not allow the individual to effectively adjust muscle preactivation to adapt to the landing impact [4]; moreover, 2.1. Participants. The subjects involved in the study were 20 SSC fatigue after exercise leads to decreased stretch-reflex healthy male Division III athlete volunteers (age = 21:5±0:9 sensitivity and muscle injury during DJ training [19]. When years old, height = 174:6±4:7 cm, weight = 67:9±7:9 kg) repeated DJs performed with more extended lower extremi- from Jilin Sport University. None of the subjects had a history ties, the individuals induced muscle fatigue will increase of muscle or bone issues in the lower extremity or neurological ankle plantar flexion to absorb the impact forces as the disease within 2 years. The procedure and possible risks were compensation for increased knee extension and the change explained to subjects, and they signed written consent forms in landing strategy under this circumstance results in poor before the study began. The study was approved by the jumping performance [20]. A study showed that muscle per- regional ethics committee, and all subjects signed informed formance changed after DJs100 was repeated, and knee joint consent forms (JLSU-IRB2020004). extensor fatigue caused the jump height to decrease by 26 ±14% [21]. Therefore, repeated DJ training is likely to 2.2. Protocol. Before the study, the subjects performed a stan- induce lower extremity fatigue and muscle injury, and jumps dard dynamic warm-up for the major muscle groups of the from the optimal drop height and the optimal training lower limbs (running on a treadmill at a speed of 8 km/h volume for DJs can prevent the risk of poor performance for 10 minutes). During the study, the subjects wore standard and injury caused by excessive fatigue and help individuals shoes provided by the laboratory to control for differences in complete reinforcement training. the absorption characteristics of the soles of shoes. Three DJ The risk of lower extremity injury may be related to experiments (DJH30, DJH40, DJH50) were conducted in a changes in joint stiffness; excessive joint stiffness increases random order over 3 separate days, with 4 days of rest the risk of bone injury, while insufficient joint stiffness may between each dropping height experiment. Before data col- lead to joint instability and soft tissue injury [22]. DJ training lection, the subjects were required to practice the jump five from different drop heights is widely used to assess the risk of times to ensure that their hands were on their waist and their lower extremity injury [5], so drop height is a key factor feet were on the two force plates during the experiment. The affecting joint stiffness during landing. The optimal drop subjects were encouraged to jump with maximum effort height can regulate the lower extremity stiffness, leading to within the shortest ground contact time [26]. The data for the best SSC to enhance jumping performance [23]. Previous DJ1, DJs50, DJs100, DJs150, and DJs200 were recorded, Applied Bionics and Biomechanics 3 and a 10-second break was provided between jumps. The K was calculated by the following formula: joint framework for the proposed methodology is shown in Figure 1. ΔM ht joint K BW ∗ = , ð2Þ joint rad Δθ 2.3. Data Collection. Twenty-one reflective markers (19 mm joint in diameter) were attached to anatomical landmarks on the legs and pelvis to define a seven-segment rigid link model where the change in joint moment between the instant of of the lower extremities, according to the Helen Hayes peak joint flexion and ground contact is defined as ΔM joint marker set [27]. The three-dimensional (3D) trajectories of and the angular displacement between the maximum joint the reflective markers on the participants were collected with flexion and the contact position is Δθ . joint 10 cameras (BTS DX400, BTS Bioengineering, Milano, Italy) at a sampling frequency of 200 Hz. Two force plates (40 ∗ 60 2.5. Statistical Analysis. The MATLAB software (R2016a; cm) were used to collect GRF data during each trial at a sam- MathWorks, Inc., Natick, MA) was used for various statisti- pling frequency of 400 Hz (BTS P6000, BTS Bioengineering, cal analysis. The variables were analyzed using one-way Milano, Italy). The infrared camera data were synchronized ANOVA repeated measure for DJH30, DJH40 and DJH50 with the force plate data via the Qualisys 64 channel A/D at DJ1, DJs50, DJs100, DJs150, and DJs200. When significant plate. results were found, post hoc analysis was performed with LSD (p <0:05) pairwise comparisons to compare the mea- 2.4. Data Analysis. A kinematic model was generated by sured values between different drop heights. The effect size defining the skeletal segments (foot, talus, shank, thigh of (ES) is used to determine whether a difference is a practical both extremities, and pelvis) in the standing trial. The central correlation difference. The modified Cohen scale was used position of the hip joint was calculated by the method pro- to determine the size of variation differences in three drop posed by Bell et al. [28]. The center of the ankle joint was height, <0.2 means trivial difference, 0.2-0.6 means small dif- defined as the midpoint between the medial and lateral ference, 0.6-1.2 means moderate difference, and 1.2-2.0 malleolus. The midpoint between the medial and lateral epi- means large difference [29]. condyles was defined as the knee joint center. The anatomic coordinate systems of the thigh and shank were determined 3. Results by the static calibration test. The vertical axis was defined as the line from the distal to proximal centers of the joint, Figure 2 presents the mean deviations of each dependent while the anteroposterior axis was perpendicular to the verti- kinematic variable of the lower extremities. Jumping height cal axis; the third axis was defined as the cross product of the and contact time increased significantly overall (all p < anteroposterior and vertical axes and used to obtain the 0:005) across the three increasing drop heights, and post dynamic coordinate systems of the pelvis, thigh, and shank. hoc analysis revealed significant differences between We performed all calculations using a custom MATLAB DJH30, DJH40, and DJH50. Our results show that jumping program (Mathworks, Natick, RI, USA). height was 1.05-, 1.08-, 1.04-, 1.07-, and 1.08-fold higher The landing phase was defined as the time interval from (all p <0:048; ES varying from 0.48 to 0.73) during DJH40 when the foot contacted the ground to the lowest center-of- than DJH30; 1.13-, 1.15-, 1.07-, 1.13-, and 1.16-fold higher mass position. A fourth-order low-pass Butterworth digital (all p <0:006; ES varying from 0.71 to 1.35) during DJH50 filter with a cutoff frequency of 50 Hz was used to smooth than DJH30; and 1.07-, 1.07-, 1.04-, 1.06-, and 1.07-fold the GRF data. Jumping height (JH) was calculated by the fol- higher (all p <0:046; ES varying from 0.48 to 0.67) during lowing formula: JH = gT /8. Contact time (CT) was defined DJH50 than DJH40 at DJ1, DJs50, DJs100, DJs150, and as the time from initial ground contact to toe-off during the DJs200, respectively (Figure 2(a)). The post hoc comparisons foot ground contact phase. The reaction strength index showed that contact time was 1.08-, 1.08-, 1.09-, 1.08-, and (RSI) was calculated as follows: RSI = JH/CT. The peak 1.07-fold higher (all p <0:049; ES varying from 0.47 to vertical ground reaction force (PVGRF) was defined as the 0.68) during DJH40 than DJH30; was 1.19-, 1.23-, 1.24-, maximum PVGRF at the initial point of contact with the 1.23-, and 1.18-fold higher (all p <0:002; ES varying from ground to the maximum angle of knee flexion. The PGRF 0.85 to 1.57) during DJH50 than DJH30; and 1.10-, 1.13-, was normalized by the subjects’ body weight (BW). 1.13-, 1.14-, and 1.11-fold higher (all p <0:041; ES varying K was calculated using the following formula: leg from 0.49 to 0.82) during DJH50 than DJH40 at DJ1, DJs50, DJs100, DJs150, and DJs200, respectively (Figure 2(b)). The reaction strength index value during vertical GRF ht hip−lowest DJH50 was significantly higher than DJH30 and DJH40 K BW ∗ = , ð1Þ leg rad ΔL leg (p <0:050), and the post hoc comparisons showed that dur- ing DJH50 was 1.14-fold (p =0:048; ES = 0:47) higher than DJH30 and 1.14-fold (p =0:021; ES = 0:56) higher than where the vertical GRF at the lowest position of the hip joint DJH40 at DJ1. The reaction strength index value during is the vertical GRF and ΔL represents the vertical DJH40 was significantly higher than DJH30 and DJH50 (all hip−lowest leg displacement of the hip from the contact position to the p <0:050), and the post hoc comparisons showed that the lowest position [26]. values were 1.08-, 1.06-, 1.12-, and 1.17-fold higher (all 4 Applied Bionics and Biomechanics Running on a treadmill at a speed Warm up of 8km/h for 10 minutes Markers attach Jumping with the maximum effort Five DJs for practice in the shortest ground contact time DJs200 from DJH30 cm R andomization DJ1, DJs50, DJs100, DJs150 and DJs200 from DJH40 cm DJs200 for data analysis DJs200 from DJH50 cm Figure 1: Framework for the proposed methodology. p <0:028; ES varying from 0.54 to 0.74) during DJH40 than decreased significantly overall (all p <0:050) across the three DJH30 and were 10.26%, 13.94%, 14.87%, and 13.14% lower increasing drop heights, with the post hoc results showing during DJH50 than DJH40 (all p <0:029; ES varying from differences between DJH30, DJH40, and DJH50. The post 0.53 to 0.70) at DJs50, DJs100, DJs150, and DJs200, respec- hoc comparisons showed that the leg stiffness was lower dur- tively (Figure 2(c)). ing DJH40 than DJH30, with ∇ values of 10.46%, 15.43%, Figure 2 presents the mean deviations of each dependent 17.62%, 12.38%, and 7.53% (all p <0:047; ES varying from ground reaction force variable for the lower extremities. The 0.48 to 0.64) and lower during DJH50 than DJH30, with ∇ peak ground reaction force and leg ground reaction force sig- values of 20.97%, 30.05%, 32.03%, 25.06%, and 23.82% (all nificantly increased overall (all p <0:050) across the three p <0:030; ES varying from 0.53 to 0.87) at DJ1, DJs50, increasing drop heights, with the post hoc results showing DJs100, DJs150, and DJs200, respectively; the values were differences between DJH30, DJH40, and DJH50. The post lower during DJH50 than DJH40, with ∇ values of 17.28%, hoc comparisons showed that peak ground reaction force 18.31%, 14.47%, and 17.62% (all p <0:043; ES varying from was 1.05-, 1.05-, and 1.07-fold higher (all p <0:018; ES vary- 0.49 to 0.58) at DJs50, DJs100, DJs150, and DJs200, respec- ing from 0.59 to 0.84) during DJH40 than DJH30 at DJs100, tively (Figure 3(a)). The post hoc comparisons showed that DJs150, and DJs200, respectively; 1.20-, 1.18-, 1.20-, 1.17-, ankle stiffness during DJH40 was lower than DJH30, with ∇ and 1.21-fold higher (all p <0:001; ES varying from 1.03 to values of 19.35%, 32.00%, 25.00%, 19.30%, and 19.09% (all 2.23) during DJH50 than DJH30; and 1.19-, 1.15-, 1.14-, p <0:040; ES varying from 0.18 to 0.91) and lower during 1.11-, and 1.13-fold higher (all p <0:001; ES varying from DJH50 than DJH30, with ∇ values of 25.81%, 30.40%, 0.91 to 1.82) during DJH50 than DJH40 at DJ1, DJs50, 37.88%, 23.68%, and 30.00% (all p <0:019; ES varying from DJs100, DJs150, and DJs200, respectively (Figure 2(e)). The 0.22 to 0.78) at DJ1, DJs50, DJs100, DJs150, and DJs200, post hoc comparisons showed that the right leg ground reac- respectively (Figure 3(d)). There were no significant differ- tion force was 1.11-, 1.05-, and 1.06-fold higher (all p <0:022; ences in knee or hip stiffness between DJH30, DJH40, and ES varying from 0.56 to 0.86) during DJH40 than DJH30 at DJH50 (Figures 3(b) and 3(c)). DJs100, DJs150, and DJs200, respectively; 1.17-, 1.21-, 1.23-, 1.16-, and 1.18-fold higher (all p <0:002; ES varying from 0.87 to 1.25) during DJH50 than DJH30; and 1.24-, 1.15 4. Discussion 1.11-, 1.11-, and 1.11-fold higher (all p <0:008; ES varying from 0.67 to 1.77) during DJH50 than DJH40 at DJ1, The purposes of this study were to investigate the effects of DJs50, DJs100, DJs150, and DJs200, respectively highly repetitive DJs from DJH30, DJH40, and DJH50 on (Figure 2(d)). The post hoc comparisons showed that the left lower extremity kinematics and stiffness and to determine leg ground reaction force was 1.15-, 1.13-, 1.14-, 1.14-, and the appropriate drop height and training volume of drop 1.15-fold higher (all p <0:050; ES varying from 0.56 to jump training. The results show that jumping height and 1.04) during DJH50 than DJH30 at DJ1, DJs50, DJs100, contact time reached the maximum values within DJs200 at DJs150, and DJs200, respectively, and 1.08-, 1.10-, and DJH50, and training at this height and volume can improve 1.11-fold (all p <0:005; ES varying from 0.72 to 0.81) higher jumping performance; however, the large ground reaction than during DJH40 at DJs100, DJs150, and DJs200, respec- force generates a high impact force, which can easily lead to tively (Figure 2(f)). lower extremity injury. Leg and ankle stiffness are maximal Figure 3 presents the mean deviations of each dependent at DJH30, which can reduce the risk of lower extremity mus- lower extremity stiffness variable. The leg and ankle stiffness culoskeletal injury and effectively utilize stretch-shortening Applied Bionics and Biomechanics 5 DJs100 DJs100 42 †‡ †‡ † DJs150 DJs150 0.4 † †‡ †‡ DJs50 †‡ DJs50 †‡ † 0.2 † 0 0.0 DJs200 DJs200 –14 †‡ –0.2 †‡ †‡ †‡ –28 DJ1 DJ1 –0.4 –42 (a) (b) DJs100 DJs100 †‡ 1.8 DJs150 DJs150 1.2 24 DJs50 † DJs50 †‡ †‡ 0.6 0.0 –12 DJs200 –0.6 DJs200 †‡ †‡ †‡ –24 –1.2 DJ1 DJ1 –36 –1.8 –48 (c) (d) DJs100 DJs100 †‡ †‡ DJs150 DJs150 1.2 †‡ †‡ † DJs50 †‡ DJs50 0.6 0 0.0 –1 DJs200 DJs200 –0.6 †‡ † †‡ †‡ –2 DJ1 DJ1 –1.2 –3 DJH30 DJH40 DJH50 (e) (f) Figure 2: The jumping height, contact time, reaction strength index, the peak vertical GRF, and right and left leg GRF during drop jumps from three heights at DJ1, DJs50, DJs100, DJs150, and DJs200. Asterisk † indicates that a significant difference with DJH30; ‡ indicates that a significant difference with DJH40; § indicates that a significant difference with DJH50. p values <0.05 were considered to significantly differ. cycle benefits to store and release elastic energy to improve can follow the natural trend of the substrate recoil, thus wast- jumping performance. ing a minimum amount of energy [32]. In this study, jump- In this study, within DJs200, jumping height and contact ing height increased gradually with drop height, which may time gradually increased with increasing drop height. Previ- have been caused by the jumping ability increasing with ous studies have shown that jumping height and contact time increasing contact time. Therefore, the DJH50 height had a increase with increasing drop height [6, 30] and that the longer contact time than did different jumps and exhibited training intensity can be enhanced and the values of jump a jumping height increase, which may have produced a better parameters such as jumping height and contact time can be training effect. In this study, reaction strength index was influenced by the drop height [6]. However, some studies higher during DJH50 than during DJH30 and DJH40 at have shown that jumping height decreases with drop height DJ1, while when landing, the reaction strength index was [6]. Increased contact time results in increased knee flexion higher during DJH40, than during DJH30 and DJH50 at to absorb the increased landing force and thus greater jump- DJs50, DJs100, DJs150, and DJs200. The differences in reac- ing ability [7, 31]. And the long contact time with the ground tion strength index according to the drop height and jump Jumping height (cm) PGRF (BW) RSI (cm/s) LGRF (BW) RGRF (BW) Contact time (s) 6 Applied Bionics and Biomechanics DJs100 DJs100 0.08 DJs150 ‡ 0.06 DJs150 3.2 DJs50 0.04 DJs50 1.6 0.02 0.0 0.0 –0.02 DJs200 DJs200 –1.6 –0.04 DJ1 DJ1 –3.2 –0.06 –0.08 (a) (b) DJs100 DJs100 0.15 0.2 DJs150 DJs150 0.10 DJs50 DJs50 0.1 0.05 0.0 0.00 DJs200 DJs200 –0.05 –0.1 DJ1 DJ1 –0.10 –0.2 –0.15 DJH30 DJH40 DJH50 (c) (d) Figure 3: The right leg, hip, knee, and ankle stiffness during drop jumps from three heights at DJ1, DJs50, DJs100, DJs150, and DJs200. Asterisk † indicates that a significant difference with DJH30; ‡ indicates that a significant difference with DJH40; § indicates that a significant difference with DJH50. p values <0.05 were considered to significantly differ. time are due to the changes in jumping height and contact findings, our results show that the resistance training inten- time. The higher the jumping height and the shorter the con- sity can be controlled by the drop height, resulting in the ground reaction force gradually increasing with increasing tact time are, the higher the reaction strength index [33, 34]. Too high of a drop height altitude will produce a large land- drop height [35]. High drop heights cause individuals to land ing impact and is not conducive to muscle fine-tuning which during DJs with high impact intensity [6], which can lead to can even decrease rather than increase power output; after ankle sprains, anterior cruciate ligament tears, and patellofe- repeated DJs, muscle fatigue will lead to a smaller stretch- moral pain syndrome [36]. Therefore, landing with high shortening cycle benefit and reaction strength index differ- impact during DJH50 can cause lower extremity injury and ence at different drop heights [4, 8, 19]. Thus, the gradual is not suitable for repeated contact time training. There were increase in drop height may lead to a change in the reaction significant differences in ground reaction force between strength index difference when the DJH40 and DJH50 jump DJH30 and DJH40 at DJs100, DJs150, and DJs200. These dif- times are different. This study showed that after DJ1, the ferences may have been caused by the differences in the initial DJH40 height produces a larger reaction strength index, peak vertical ground reaction force at ground contact due to which can have a larger training effect, while after repeat fatigue and individual changes in joint stiffness [17, 37]. drop jump training at the DJH50 height, muscle fatigue Therefore, the impact force can be changed by controlling may decrease the stretch-shortening cycle benefit, resulting the training intensity at different drop heights. In this study, in a decrease in the reaction strength index. Therefore, drop smaller ground reaction forces reduced the risk of lower heights of DJH40 and DJH50 can produce greater reaction extremity musculoskeletal injury when landing at DJ1, strength index values, and the reaction strength index value DJs50, DJs100, DJs150, and DJs200 from the height of may be more suitable for drop jump training; however, train- DJH30. In this study, during landing from DJH40 and DJH50 ing from DJH50 for 200 consecutive times produces a lower reaction strength index, which may easily cause muscle within DJs200, the stiffnesses of the legs and ankle joints were fatigue and poor jumping performance. lower than those during landing from DJH30, while there The results of this study show that the ground reaction were no differences in the stiffnesses of the knees and hips force produced at DJH50 within DJs200 is greater than those between other drop heights. Consistent with previous find- ings, the stiffnesses of the legs and ankle gradually decreased produced at DJH30 and DJH40. Consistent with previous Hip stiffness(BW ht/rad) Leg stiffness(BW ht/rad) ⁎ ⁎ Ankle stiffness(BW ht/rad) Knee stiffness(BW ht/rad) Applied Bionics and Biomechanics 7 and stiffness by the drop height will affect the stability of with increasing drop height, while the stiffnesses of the knees and hips did not significantly differ across drop heights [6, the knee joint. Within DJs200, training at the height of 26, 38]. The ankle stiffness decreased gradually with increas- DJH50 can yield better jumping performance; however, ing drop height, resulting in a decrease in the stretch- because the high impact easily leads to lower extremity shortening cycle benefit when drop jump training [6]; there- injury, training at the drop height of DJH30 can increase fore, the smaller ankle stiffness may have affected the training the stiffnesses of the legs and ankle joints, thus effectively uti- effect. Increasing stiffness enables better storage and release lizing the SSC benefits to store and release elastic energy, of stretch-shortening cycle-based elastic energy [38]. In addi- improving jumping performance and reducing the risk of tion, jumping training can increase the joint stiffness of the lower extremity musculoskeletal injury. lower extremities during landing, reduce the risk of injury, and improve athletic performance by strengthening the Abbreviations lower extremity muscles [39]. The higher leg and ankle stiff- DJ: Drop jump nesses generated by highly repetitive drop jump training at DJH: Drop jump height DJH30 in this study can lead to greater stretch-shortening JH: Jumping height cycle benefits regarding the storage and release of elastic CT: Contact time energy and reduce the incidence of lower extremity injuries, SSC: Stretch-shortening cycle which may be suitable for repetitive drop jump training. Past RSI: Reaction strength index studies have shown that the longer the contact time at drop BWs: Body weights jump landing is, the lower the stiffness of the lower extremi- ES: Effective size ties [40]. In this study, contact time increased gradually with GRF: Ground reaction force increasing drop height, so the stiffnesses of the legs and ankle PGRF: Peak ground reaction force may be related to the increase in contact time. Therefore, if RGRF: Right leg ground reaction force athletes can consciously control the contact time during LGRF: Left leg ground reaction force training, they may adjust the lower extremity stiffnesses at PVGRF: Peak vertical ground reaction force. landing according to the drop height. The stiffnesses of lower extremity joints are affected by joint torques. In this study, the knee and hip stiffnesses showed no differences after Data Availability repeated drop jump training, which may have occurred The data results are included in the manuscript. because the knee and hip torques did not change significantly between the drop heights. In summary, drop jump training Conflicts of Interest with the appropriate lower extremity stiffness or stiffness adjustments during repeated jumping training can reduce All authors declare that they have no conflicts of interest with the risk of lower extremity injury and enhance the training regard to the contents of this article. effect. This study showed that landing from the DJH30 height within DJs200 produces larger leg and ankle stiffnesses, Authors’ Contributions which can yield greater stretch-shortening cycle benefits, thereby improving jumping performance and reducing the YMC and ILW designed the experiments. YMC, ILW, and risk of lower extremity injury, so these parameters are YSC carried out the supplement preparation and laboratory suitable for repeated drop jump training. experiments. ILW, WCC, and YMC analyzed the data, inter- preted the results, prepared the figures, and wrote the 4.1. Limitations. Limitations need to be considered when manuscript. WCC, SZ, and YMC contributed the reagents, interpreting the results. Firstly, amounts of drop height are materials, and the analysis platforms. not sufficient, so we need lower and higher DJH such as 20 cm and 60 cm. Secondly, the subjects were obviously not Acknowledgments blinded to the DJH, so the central nervous system may apply a protective strategy, and this could introduce performance The authors would like to thank all colleagues and students bias. Thirdly, electromyographic was not used in this study, who contributed to this study. This work was supported by so the activity of the lower limb muscles is unknown during the Research on Hubei province education department landing and jumping. science and technology research program (grant number D20202502). This manuscript was edited by American Jour- 5. Conclusion nal Experts Editing. In summary, with increasing drop height, the kinematics and References stiffnesses of the lower extremities varied during landing. DJ training from a high drop height produces a high impact [1] M. Walsh, A. Arampatzis, F. Schade, and G. P. Brüggemann, intensity, resulting in a greater impact. Compared with the “The effect of drop jump starting height and contact time on heights of DJH30 and DJH40, the DJH50 height yielded power, work performed, and moment of force,” Journal of higher JH, CT, and GRF values, as well as smaller leg and Strength and Conditioning Research, vol. 18, no. 3, pp. 561– ankle stiffnesses during landing; the changes in kinematics 566, 2004. 8 Applied Bionics and Biomechanics [18] P. V. Komi and A. Gollhofer, “Stretch reflexes can have an [2] D. Matavulj, M. Kukolj, D. Ugarkovic, J. Tihanyi, and S. Jaric, “Effects of pylometric training on jumping performance in important role in force enhancement during SSC exercise,” junior basketball players,” Journal of sports medicine and phys- Journal of applied biomechanics, vol. 13, no. 4, pp. 451–460, ical fitness, vol. 41, no. 2, pp. 159–164, 2001. 1997. [3] K. J. Simpson and L. Kanter, “Jump distance of dance landings [19] T. Horita, P. Komi, I. Hämäläinen, and J. Avela, “Exhausting influencing internal joint forces: I. Axial forces,” Medicine and stretch-shortening cycle (SSC) exercise causes greater impair- science in sports and Exercise, vol. 29, no. 7, pp. 916–927, 1997. ment in SSC performance than in pure concentric perfor- mance,” European Journal of Applied Physiology, vol. 88, [4] V. Mrdakovic, D. B. Ilic, N. Jankovic, Z. Rajkovic, and no. 6, pp. 527–534, 2003. D. Stefanovic, “Pre-activity modulation of lower extremity muscles within different types and heights of deep jump,” Jour- [20] J. T. Weinhandl, J. D. Smith, and E. L. Dugan, “The effects of nal of sports science and medicine, vol. 7, no. 2, p. 269, 2008. repetitive drop jumps on impact phase joint kinematics and kinetics,” Journal of Applied Biomechanics, vol. 27, no. 2, [5] H.-T. Peng, T. W. Kernozek, and C. Y. Song, “Quadricep and pp. 108–115, 2011. hamstring activation during drop jumps with changes in drop height,” Physical Therapy in Sport, vol. 12, no. 3, pp. 127–132, [21] K. Kubo, H. Kanehisa, and T. Fukunaga, “Influences of repet- 2011. itive drop jump and isometric leg press exercises on tendon properties in knee extensors,” Journal of strength and condi- [6] H.-T. Peng, “Changes in biomechanical properties during tioning research, vol. 19, no. 4, pp. 864–870, 2005. drop jumps of incremental height,” Journal of Strength and Conditioning Research, vol. 25, no. 9, pp. 2510–2518, 2011. [22] R. J. Butler, H. P. Crowell III, and I. M. C. Davis, “Lower extremity stiffness: implications for performance and injury,” [7] N. B. Ball, C. G. Stock, and J. C. Scurr, “Bilateral contact Clinical biomechanics, vol. 18, no. 6, pp. 511–517, 2003. ground reaction forces and contact times during plyometric drop jumping,” Journal of Strength and Conditioning Research, [23] P. J. Byrne, K. Moran, P. Rankin, and S. Kinsella, “A compar- vol. 24, no. 10, pp. 2762–2769, 2010. ison of methods used to identify ‘Optimal’ Drop height for early phase adaptations in depth jump training,” Journal of [8] M. Ruan and L. Li, “Influence of a horizontal approach on the Strength and Conditioning Research, vol. 24, no. 8, pp. 2050– mechanical output during drop jumps,” Research quarterly for 2055, 2010. exercise and sport, vol. 79, no. 1, pp. 1–9, 2008. [24] N. J. Chimera, K. A. Swanik, C. B. Swanik, and S. J. Straub, [9] M. S. Matic, N. R. Pazin, V. D. Mrdakovic, N. N. Jankovic, “Effects of plyometric training on muscle-activation strategies D. B. Ilic, and D. L. J. Stefanovic, “Optimum drop height for and performance in female athletes,” Journal of athletic train- maximizing power output in drop jump: the effect of maximal ing, vol. 39, no. 1, pp. 24–31, 2004. muscle strength,” Journal of Strength and Conditioning Research, vol. 29, no. 12, pp. 3300–3310, 2015. [25] W. Taube, C. Leukel, B. Lauber, and A. Gollhofer, “The drop height determines neuromuscular adaptations and changes [10] S. McInnes, J. S. Carlson, C. J. Jones, and M. J. McKenna, “The in jump performance in stretch-shortening cycle training,” physiological load imposed on basketball players during com- Scandinavian journal of Medicine and Science in Sports, petition,” Journal of Sports Sciences, vol. 13, no. 5, pp. 387–397, vol. 22, no. 5, pp. 671–683, 2012. [26] I.-L. Wang, S. Y. Wang, and L. I. Wang, “Sex differences in [11] C. Thomas, I. Kyriakidou, T. Dos’Santos, and P. A. J. S. Jones, lower extremity stiffness and kinematics alterations during “Differences in vertical jump force-time characteristics double-legged drop landings with changes in drop height,” between stronger and weaker adolescent basketball players,” Sports biomechanics, vol. 14, no. 4, pp. 404–412, 2015. Sports, vol. 5, no. 3, p. 63, 2017. [12] U. Alemdaroğlu, “The relationship between muscle strength, [27] I.-L. Wang et al., “Nanobubbles water curcumin extract reduces injury risks on drop jumps in women: a pilot study,” anaerobic performance, agility, sprint ability and vertical jump performance in professional basketball players,” Journal of Evidence-Based Complementary and Alternative Medicine, vol. 2019, Article ID 8647587, 9 pages, 2019. human kinetics, vol. 31, no. 1, pp. 149–158, 2012. [13] M. F. Bobbert, “Drop jumping as a training method for jump- [28] A. L. Bell, D. R. Pedersen, and R. A. Brand, “A comparison of the accuracy of several hip center location prediction ing ability,” Sports medicine, vol. 9, no. 1, pp. 7–22, 1990. methods,” Journal of biomechanics, vol. 23, no. 6, pp. 617– [14] W. R. Holcomb, J. E. Lander, R. M. Rutland, and G. D. Wilson, 621, 1990. “The effectiveness of a modified plyometric program on power and the vertical jump,” Journal of Strength and Conditioning [29] W. G. Hopkins, S. W. Marshall, A. M. Batterham, and Research, vol. 10, no. 2, pp. 89–92, 1996. J. Hanin, “Progressive statistics for studies in sports medicine and exercise science,” Medicine and Science in Sports and Exer- [15] G. J. Wilson, R. U. Newton, A. J. Murphy, and B. J. Humphries, cise, vol. 41, no. 1, pp. 3–13, 2009. “The optimal training load for the development of dynamic [30] H.-T. Peng, C. T. Khuat, T. W. Kernozek, B. J. Wallace, S. L. athletic performance,” Medicine and Science in Sports and Exercise, vol. 25, no. 11, pp. 1279–1286, 1993. Lo, and C. Y. Song, “Optimum drop jump height in division III athletes: under 75% of vertical jump height,” International [16] M. F. Bobbert, P. A. Huijing, and G. J. van Ingen Schenau, journal of sports medicine, vol. 38, no. 11, pp. 842–846, 2017. “Drop jumping. I. The influence of jumping technique on the [31] W. J. Markwick, S. P. Bird, J. J. Tufano, L. B. Seitz, and G. G. biomechanics of jumping,” Medicine and Science in Sports and Exercise, vol. 19, no. 4, pp. 332–338, 1987. Haff, “The intraday reliability of the reactive strength index calculated from a drop jump in professional men’s basketball,” [17] T. Horita, P. Komi, C. Nicol, and H. Kyröläinen, “Interaction International Journal of Sports Physiology and Performance, between pre-landing activities and stiffness regulation of the vol. 10, no. 4, pp. 482–488, 2015. knee joint musculoskeletal system in the drop jump: implica- tions to performance,” European journal of applied physiology, [32] X. Mo, D. Romano, M. Miraglia, W. Ge, and C. Stefanini, vol. 88, no. 1-2, pp. 76–84, 2002. “Effect of substrates' compliance on the jumping mechanism Applied Bionics and Biomechanics 9 of Locusta migratoria,” Frontiers in bioengineering and bio- technology, vol. 8, p. 661, 2020. [33] K. Beattie, B. P. Carson, M. Lyons, and I. C. Kenny, “The rela- tionship between maximal strength and reactive strength,” International Journal of Sports Physiology and Performance, vol. 12, no. 4, pp. 548–553, 2017. [34] C. Feldmann, L. W. Weiss, L. C. Ferreira, B. K. Schilling, and K. G. Hammond, “Reactive strength index and ground contact time: reliability, precision, and association with drop vertical jump displacement,” Journal of Strength and Conditioning Research, vol. 25, p. S1, 2011. [35] H. Makaruk and T. Sacewicz, “The effect of drop height and body mass on drop jump intensity,” Biology of Sport, vol. 28, no. 1, pp. 63–67, 2011. [36] B. D. Beynnon, P. M. Vacek, D. Murphy, D. Alosa, and D. Paller, “First-time inversion ankle ligament trauma: the effects of sex, level of competition, and sport on the incidence of injury,” The American journal of sports medicine, vol. 33, no. 10, pp. 1485–1491, 2005. [37] C. Nicol, P. Komi, and P. Marconnet, “Fatigue effects of mar- athon running on neuromuscular performance: I. Changes in muscle force and stiffness characteristics,” Scandinavian Jour- nal of Medicine and Science in Sports, vol. 1, no. 1, pp. 10–17, [38] L. Wang and H. T. Peng, “Biomechanical comparisons of single-and double-legged drop jumps with changes in drop height,” International Journal of Sports Medicine, vol. 35, no. 6, pp. 522–527, 2014. [39] M. J. Barr and V. W. Nolte, “The importance of maximal leg strength for female athletes when performing drop jumps,” Journal of Strength and Conditioning Research, vol. 28, no. 2, pp. 373–380, 2014. [40] A. Arampatzis, F. Schade, M. Walsh, and G. P. Brüggemann, “Influence of leg stiffness and its effect on myodynamic jump- ing performance,” Journal of electromyography and kinesiol- ogy, vol. 11, no. 5, pp. 355–364, 2001.

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Applied Bionics and BiomechanicsHindawi Publishing Corporation

Published: Mar 4, 2021

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