Introduction
In an attempt to emulate barefoot conditions, minimal footwear are constructed with lighter and more flexible materials and have a lower heel-to-toe drop than standard footwear (12). The effects of minimal footwear on running biomechanics as they relate to injury risks and performance have been investigated (15). Few studies have investigated the biomechanical implications of wearing minimal footwear during sporting tasks other than running such as jumping. Vertical jumping displacement is predictive of sport performance (4,9,10). Therefore, understanding the effects of footwear on jump performance is of interest to athletes, coaches, and trainers.
There is currently contradicting evidence of footwear effects on countermovement vertical jump (CMVJ) displacement (5,11,16,18). Differences in the definition of minimal footwear, study design, and tested population may explain the different footwear effects on jumping performance in the literature. Minimal footwear produce lower soleus but higher vastus medialis muscle activation during the concentric phase of jumping compared with standard training shoes when jumping performance is not different between minimal and standard footwear (16). These differences in muscle activity between footwear may suggest lower plantarflexor and higher knee extensor mechanical outputs during jumping. However, the amplitude of muscle activity is not directly related to muscle force production during dynamic contractions (30). Because minimal footwear yields greater peak-negative and peak-positive sagittal ankle power and work but smaller peak-negative and peak-positive sagittal knee power and work compared with neutral cushioning shoes during the propulsive phase of running (14,24), similar differences in joint kinetics between footwear may be expected during CMVJ. Peak sagittal ankle and hip power production are both good predictors of CMVJ performance (2), and therefore, comparing lower-limb joint kinetics during jumping would provide useful insight regarding potential loci of adaptation from CMVJ training in different footwear. Joint mechanics data could serve as justification for joint-specific CMVJ training programming using different footwear.
Kinetic variables during CMVJ, including lower concentric peak power of vertical ground reaction force (GRF) (22) and peak vertical GRF during propulsion (26), may explain sex differences in jumping performance (8). These mechanical sex differences have been attributed to greater type II muscle fiber force production capacity (23), longer and thicker quadriceps fascicles (1), and more quadriceps muscle mass (23,27) in men. If men can produce more force with larger muscles, this would explain much of the sex difference in CMVJ performance. Lower-limb joint powers and work are often measured to explain joint function during CMVJ performance (13,16). These kinetic parameters may provide mechanisms to explain any sex or footwear effects on jumping performance.
The purpose of this investigation was to examine effects of footwear and sex on CMVJ performance and lower-limb sagittal plane joint kinetics. We expected no footwear effects on CMVJ displacement but greater sagittal peak-positive and peak-negative ankle joint powers and lower peak-positive and peak-negative knee powers in minimal compared with standard footwear. We also expected greater CMVJ displacement in men compared with women, and men would jump with greater peak moments and negative and positive joint kinetics compared with women because power is related to vertical jump performance. The findings of this investigation could be important to coaches because they will provide joint- and sex-specific jumping mechanics in different footwear that may help in programming details of vertical jump training.
Methods
Experimental Approach to the Problem
Although there seems to be no difference in maximal vertical jump height when jumping in minimal or standard footwear in men, this study aimed to understand whether wearing different footwear when jumping could alter jump performance and lower-limb joint mechanical output in men and women. We performed a mixed-design comparison of lower-limb joint kinetics during maximal vertical jumping in standard and minimal footwear in young men and women. This study was performed to understand whether footwear affected lower-limb joint kinetic contributions during jumping and whether footwear or jumping strategy explained why men jump higher than women.
Subjects
An a priori power analysis (G*Power, Düsseldorf, Germany) indicated that a total of 24 participants would be needed to obtain an F-test effect size f of 0.3, power of 0.80, and alpha level of 0.05 with 2 within-subject factors (footwear) and 2 between-subject factors (sex). As data from current literature could not be used to compute an effect size, an estimated F-test effect size f of 0.3 was selected to obtain a robust estimate of the required sample size. Twelve men and 12 women were recruited to participate in this study. Participants were recreationally trained college students aged between 18 and 30 years who trained at least 3 times per week and included vertical jumping movements in their training or sports activities (e.g., intramural sports) (Table 1). Participants were free of lower-body injury at time of testing and had never undergone any lower-limb surgeries. Before participation, each participant was informed of all procedures, potential risks, and benefits associated with the study through both verbal and written form in accordance with the procedures approved by the University of Memphis Institutional Review Board for Human Participants Research.
;)
Table 1.: Participant characteristics for each sex group (mean ± SD).*†
Procedures
Participant height and mass were measured using a calibrated stadiometer and digital scale, respectively. Participants performed CMVJ in 2 footwear conditions in randomized order: standard training shoe (MX623; New Balance, Boston, MA, USA) and minimal shoes (5 Finger KSO; Vibram, North Brookfield, MA, USA). The minimal index (MI) was used to quantify the level of minimalism for each footwear type (12) where 0% is the least minimal and 100% is entirely minimal. The minimal footwear had an MI of 84% with a heel-toe drop of 3.5 mm, and mass of 161.5 g while the standard training shoe had an MI of 12%, heel-toe drop of 10 mm, and mass of 358 g. All MI measures were taken with an analog caliper (Model 01291, LaFayette, IN, USA) using procedures previously described (12). A 9-camera motion capture system (240 Hz; Qualisys AB, Goteburg, Sweden) and force platform (1,200 Hz; AMTI, Watertown, MA, USA) were used to collect 3-dimensional (3D) kinematics and GRF data during all jumping trials. Participants jumped using both feet, but only the dominant foot was analyzed. Before vertical jump testing, participants completed a 5-minute stationary cycling warm-up and 3 twelve-touch dot drills. The dot-drill exercise requires the participant to jump from the center of a diamond-shaped tape arrangement on the floor to one of the 4 corners and then back to the center before jumping to the next corner, and jumping again to the center. The drill is continued for 12 foot contacts.
After the warm-up, participants wore the first footwear condition, and retroreflective markers were placed on the dominant lower extremity and pelvis. Initially, only clusters of 4 noncollinear markers on a thermoplastic semirigid shell were secured to the pelvis, thigh, and shank using a neoprene wrap, whereas a cluster of 3 noncollinear markers was secured to the heel counter of the shoe using adhesive tape. Each participant completed 3 practice vertical CMVJ trials using a Vertec (Sports Imports, Hilliard, OH, USA) instrument to provide an external target to ensure maximal effort. Three successful maximal CMJVs were then performed. A successful jump was defined by a countermovement where the feet were not repositioned during the countermovement, and the participants were able to touch the Vertec vanes with a 1-hand reach. Each jumping trial was followed by a 1-minute rest period for full recovery.
After jump trials in the first footwear condition, reflective markers were placed over specific anatomical landmarks. The pelvis was defined with iliac crests and greater trochanter markers, and the hip joint center was calculated at the location of 1-quarter the distance between the ipsilateral and contralateral greater trochanters (29). The thigh was defined by the greater trochanters and hip joint centers, and the femoral epicondyles. The shank was defined by the femoral epicondyles and the malleoli. The foot was defined with the malleoli and the first and fifth metatarsal heads. To account for the axial offset of the foot segment during standing, a modified coordinate system was created. Virtual landmarks located between the metatarsal heads and at the ankle joint center defined the anterior–posterior axis of the foot. The fifth metatarsal head marker was used to define the mediolateral axis with respect to the ankle joint location. The vertical axis of the foot segment was orthogonal to the mediolateral and anterior–posterior axes. A 1-second static calibration trial was collected to define joint centers and segment coordinate systems and dimensions. After this calibration trial, only heel cluster and metatarsal head markers were removed and participants put on the other testing footwear. The 3-marker cluster and anatomical markers were placed on the second footwear, and another calibration trial was collected specific to the second footwear condition. These procedures were used to ensure the high anatomical marker placement reliability between footwear conditions. Participants then performed 3 practice trials in the second footwear condition. Three maximal CMVJ trials were again completed using the same procedures as with the first footwear condition. Preferred stance width was used for individual participants and was controlled by placing adhesive tape over the force platforms for each participant during all jumping trials in both footwear conditions.
Data Analyses
To account for footwear sole thickness differences that could influence jump height, CMVJ displacement was calculated as the difference between peak pelvis marker height during the jump and pelvis marker height during the static trial in both footwear conditions. Visual3D biomechanical software (C-Motion, Inc., Germantown, MD, USA) was used to process and analyze all biomechanical data. Kinematic data were interpolated using a least-square fit of a third-order polynomial with a 3 data point fitting and a maximum gap of 10 frames. Kinematic and GRF data were then filtered using a fourth-order Butterworth low-pass filter with cutoff frequencies of 8 and 40 Hz, respectively. A right-hand rule was used to define joint rotation polarity, and a Cardan rotational sequence (X-y-z) was used for 3D angular computations where x represents the mediolateral axis, y represents the anteroposterior axis, and z represents the longitudinal axis. Ankle, knee, and hip joint angular kinetic variables were expressed in the shank, thigh, and pelvis coordinate systems, respectively. Newtonian inverse dynamics were used to compute net internal joint moments. Angular joint powers were computed as the dot product of joint moments and joint angular velocities. Angular joint work was calculated as the time integral of angular joint power using the trapezoidal rule. Total positive and negative lower-limb joint work was calculated as the positive and negative sum of ankle, knee, and hip angular work, respectively. Internal joint moments (N·m·kg−1), powers (W·kg−1), and work (J·kg−1) were normalized to body mass for between-group comparisons.
The CMVJ was broken down into 2 phases: countermovement phase and jumping phase. The countermovement phase (i.e., eccentric phase) was defined as the period between the initial downward movement of a posterior pelvic tracking marker and the lowest vertical position of the same pelvis marker. The jumping phase (i.e., concentric phase) was defined as the period between the lowest vertical position of the pelvis marker and takeoff (i.e., vertical GRF threshold below 20 N). Primary biomechanical variables included peak-negative joint angular powers and joint work during the countermovement and peak-positive joint angular powers and joint work during the jumping phase. Secondary biomechanical variables included peak ankle plantarflexor, knee extensor, and hip extensor moments, as well as ankle plantarflexion, knee extension, and hip extension range of motion (ROM) during both movement phases. The average of the peak joint moments and powers, and of joint work for the 3 maximal CMVJs, was used in statistical analyses to ensure a more robust analysis of each participant's movement patterns.
Statistical Analyses
Mixed-design (footwear × sex) analyses of variance were conducted for all dependent variables with footwear as the within-subject factor and sex as the between-subject factor (SPSS 23.0, Chicago, IL, USA). When interaction effects were observed, paired t-tests were used to compare footwear effects while independent t-tests were used to compare sexes. Sex differences in participant characteristics were compared using independent t-tests. Data normality was assessed using the Shapiro–Wilk test. Significance level was set at α = 0.05. Cohen's d effect sizes were also calculated to assess the magnitude of mean differences using the interpretation of Hopkins (small: d < 0.6; moderate: 0.6 < d < 1.2; large: d > 1.2) (19).
Results
Data from 1 female participant were problematic and had to be discarded from the analyses (women, n = 11). Men were heavier, taller, and had a lower body mass index than women (Table 1). No interaction (p = 0.48) or footwear main effects (p = 0.21) were observed for CMVJ displacement. A sex main effect was observed for CMVJ displacement as men (0.47 ± 0.08 m) jumped higher than women (0.28 ± 0.07 m; p < 0.001; d = 2.53; Figure 1).
Figure 1.: Countermovement vertical jump (CMVJ) displacements for women and men in standard and minimal footwear. *Sex main effect (p < 0.05).
No interaction effects were observed for peak joint moments (Table 2). A small footwear effect was observed for peak plantarflexor moment (Table 2) because standard footwear yielded smaller peak moments than minimal footwear (d = 0.20). Moderate to large sex effects were observed for peak ankle plantarflexor moment (d = 1.62), peak knee extensor moment (d = 1.62), and peak hip extensor moment (d = 0.99) (Table 2). Men jumped with greater peak plantarflexor moment, greater peak knee extensor moment, and greater peak hip extensor moment compared with women.
Table 2.: Peak moments, peak joint angular negative and positive power, and negative and positive joint work in both footwear conditions for men and women during maximal CMVJ (mean ± SD).*†
No interaction effects were observed for all peak-positive and peak-negative joint powers, and no footwear effects were observed for peak-positive ankle or hip powers. A small footwear effect (Figure 2) was observed for peak-positive sagittal knee power because minimal footwear produced smaller knee joint–positive power compared with standard footwear (d = 0.27) (Table 2). There were also moderate to large sex effects (Figure 3) for peak-positive sagittal ankle, knee, and hip powers (Table 2). Men produced greater positive ankle power (d = 1.31), knee power (d = 1.57), and hip power (d = 1.07) compared with women. There were no sex or footwear effects for peak-negative joint powers.
Figure 2.: Ensemble average curves for ankle (A), knee (B), and hip (C) angular powers during jumping in standard and minimal footwear when sex groups are pooled. *Footwear main effect (p < 0.05).
Figure 3.: Ensemble average curves for ankle (A), knee (B), and hip (C) angular powers during jumping in men and women when footwear groups are pooled. *Sex main effect (p < 0.05).
An interaction effect for total positive lower-limb joint work was observed (p = 0.01). Independent t-test revealed greater total positive work in men compared with women (d = 2.38) but only in standard footwear (Table 2). There were no main or interaction effects for total negative lower-limb joint work. There were no interaction effects for individual positive joint work, but small footwear effects for positive ankle (d = 0.34) and knee (d = 0.21) joint work were found as standard footwear yielded more joint work than minimal footwear (Table 2). Moderate to large sex effects for positive ankle (d = 1.04) and knee (d = 1.34) joint work were also observed because men produced more positive work than women (Table 2). Finally, no interaction, footwear, or sex effects was observed for negative joint work.
No interaction effects were observed for any joint ROM (Table 3). No sex or footwear effects were observed for any eccentric joint ROM or for knee and hip joint extension ROM during the jumping phase. Small footwear and moderate sex effects were observed for ankle plantarflexion ROM during the jumping phase (Table 3). Minimal footwear produced smaller ankle plantarflexion ROM compared with standard footwear (d = 0.68), and men jumped with smaller ankle plantarflexion ROM compared with women (d = 0.82) (Table 3).
Table 3.: Joint ROM during the countermovement (CM) and jumping phases in both footwear conditions for men and women during maximal CMVJ (mean ± SD).*†
Discussion
The purpose of this investigation was to examine the effects of footwear and sex on CMVJ performance and lower-limb joint sagittal powers. As expected, we did not detect any differences in CMVJ displacement between minimal and standard footwear. Previous studies have reported conflicting findings on CMVJ displacement while wearing different footwear. Contrary to our findings, research has shown higher CMVJ in minimal and barefoot conditions compared with standard footwear (5,20). Blache et al. (5) observed higher CMVJ displacement in barefoot and 6 different models of minimal footwear compared with standard basketball footwear in 1 national level basketball player. The case–study design in addition to a potential fatigue effect from performing jumps in 6 different minimal shoes in a single continuous session likely explains the contrary footwear effects on jump height. Furthermore, LaPorta et al. (20) reported greater jumping heights in minimal footwear and barefoot compared with traditional footwear. These jump height differences between footwear may be the result of footwear acclimatization because their testing protocol took place over 4 days. The exclusion of arm swing during the countermovement (20) could have also affected the footwear comparisons because the arm use influences jump performance (21). Our previous research on vertical jumping using identical footwear models included in the current study also observed no CMVJ displacement differences between footwear (16). As in the current study, those participants were allowed to use arm swing during the CMVJ. Since vertical jumping during sports generally involves arm swing actions, we suggest that CMVJ jumping, as a performance measure, is not different between standard and minimal footwear in both men and women. Although the current findings do not reveal differences in CMVJ between footwear conditions, the individual participant variances in CMVJ displacement were noteworthy. Nine of our 23 participants (5 men and 4 women) jumped slightly higher in minimal compared with standard footwear, which could be attributed to specific anthropometric or training-related factors between athletes. Although these performance differences were small (1–4 cm), previous research has noted that subtle increases in jump height (∼2 cm) are meaningful during competition (3). Thus, although certain body dimensions do not explain a large portion of the variance in CMVJ displacement (7), future studies should investigate footwear effects on jumping performance in individuals of different training backgrounds and anthropometric characteristics. Such characteristics may explain why previous research has observed footwear differences during CMVJ (20).
Our hypothesis that minimal compared with standard footwear would yield larger peak ankle powers, but lower knee joint powers were not supported. Although positive knee power and work were smaller in minimal compared with standard footwear, the effect magnitudes were small (d < 0.6). Although small, these footwear differences are in accordance with observed mechanical outputs during running (6,24), where peak-positive sagittal knee powers are greater in standard compared with minimal footwear likely due to a tendency to use a rearfoot striking pattern in standard running shoes (24). Although there is no allegory to a foot strike during CMVJ, our results suggest that standard footwear may yield a slightly more knee-dominant propulsion in jumping when compared with minimal footwear. It is doubtful that these small knee mechanical outputs have any training implications, but future studies should assess training footwear effects on jumping performance and joint mechanical output during jumping.
Contrary to our hypothesis, greater ankle mechanical output in minimal compared with standard footwear was not observed during CMVJ. Peak plantarflexor moment was in fact larger in minimal compared with standard footwear, but the small effect size suggests that this difference may not be meaningful. The similar peak ankle positive power between the current footwear is in contrast to observations during running, where minimal footwear yields greater peak-positive ankle power and peak-positive work compared with standard footwear (14,24). As expected, positive knee work and peak-positive knee power were smaller in minimal compared with standard footwear, which suggests slightly larger knee extensor contributions during jumping while wearing standard training footwear. The larger positive ankle work in standard footwear was unexpected, but because joint angular work is the product of the joint moment and angular displacement, the greater ankle work seems to be related to greater plantarflexion ROM during the jumping phase in standard compared with minimal footwear. Overall, we suggest that athletes could favor the use of standard footwear for movements akin to CMVJ when training for CMVJ displacement to increase concentric knee extensor and ankle plantarflexor work. However, considering the footwear differences were small, and the cross-sectional design of this study, future research should examine training footwear effects on individual joint mechanical output.
As expected, men jumped significantly higher and had greater peak-positive moments and powers at the ankle, knee, and hip joints in addition to greater positive ankle and knee joint work than women. The greater jump heights observed in men are echoed in other research (25,26) with anthropometric explanations of more skeletal muscle mass in men (23), thicker knee extensors (26) and longer fascicles in knee musculature in men (1), and lower body fat percentages in men (27,28). Stephens et al. (28) noted that men had lower thigh and shank body fat percentages when groups were matched for leg circumference, indicating a higher volume of muscle mass and a greater ability to produce maximal force. Men also have larger rectus femoris muscles (26) and longer vastus medialis fascicles (1), which may suggest men have a particular advantage for knee extensor force production. Furthermore, men exhibit higher rectus femoris EMG activity during the concentric portion of CMVJ compared with women (21). Higher EMG activity is potentially indicative of more motor unit recruitment and therefore greater knee extensor force generation. Another explanation for lower mechanical output and CMVJ performance in women may be attributed to women's postpubescent increases in Q-angle (25) (i.e., angle between anterior superior iliac spine and the line between the patella and tibial tuberosity). Increases in Q-angles often cause hip internal rotation and an inward collapse of the femur over the tibia during vertical jumping (25), which might predispose female jumpers to a less-efficient transfer of both vertical force during CMVJ and sagittal lower-limb joint mechanical output. It is clear that future research should examine the influence of Q-angle and nonsagittal plane lower-limb joint mechanics on jumping performance and sagittal lower-limb joint power production in men and women. Overall, our findings of greater lower-limb joint mechanical output when jumping further supports a greater capacity to produce force in men compared with women.
Contrary to our second hypothesis, none of the body mass normalized peak-negative lower-limb joint powers, and negative joint angular work was different between sexes. This is a novel and insightful finding that highlights potential joint-specific mechanical output differences between men and women during vertical jumping. Others have reported no sex differences in body mass normalized peak propulsive GRF magnitudes in strength-matched men and women (26). Our results therefore indicate that the sex differences detected for positive lower-limb joint mechanical output may be independent of body mass differences between sexes. Our results are consistent with findings of both greater absolute peak vertical power and higher CMVJ in men compared with women (26), indicating men have a greater capacity for concentric power production than women. In our study, greater positive joint mechanical output likely explains the greater CMVJ displacements in men compared with women. Although more mechanistic exploration is necessary, the similar negative (i.e., eccentric) but greater positive (i.e., concentric) joint mechanical output in men compared with women may indicate that men are able to better use the stretch-shortening cycle (SSC) to elicit an enhanced concentric response than women. In fact, recent evidence suggests that better vertical jumpers use a more rapid downward movement (i.e., unloading phase) compared with poor jumpers (17). Our finding of greater ankle plantarflexor ROM in women compared with men may explain the smaller positive peak power output in women because greater plantarflexor ROM during the concentric phase may indicate greater time of plantarflexor force application. Furthermore, research has shown increased ankle joint coactivation of the tibialis anterior and gastrocnemius during CMVJ jumping phase in women (27), which may suggest greater dorsiflexor moment contributions to the net sagittal ankle moment and a stiffer ankle joint compared with men. Too much stiffness would move through the plantarflexor ROM more slowly, reducing peak power if the net moment is unchanged. Also, Miller et al. (23) found men had stronger and larger type II vastus lateralis muscle fibers than women. However, because we did not assess muscle morphological properties in the current study, future studies should consider these measures to better understand the physiological mechanisms potentially responsible for sex differences in peak-positive joint powers during maximal CMVJ. Finally, considering the interaction effect found for total lower-limb–positive work, it seems that men are able to produce more total positive work from lower-limb joints especially in standard footwear conditions when compared with women (d = 3.85). Because no sex differences were observed in joint-specific negative work and total joint-negative work, this finding further supports the hypothesis that men, especially in standard training footwear, are capable of more optimal utilization of the SSC than women.
This study has some limitations. First, a chronic footwear acclimatization period was not provided, and therefore, only acute footwear effects were observed. We may have seen different footwear effects in joint mechanical output had we included a footwear acclimatization period, which could explain the higher CMVJ observed when some acclimatization period is provided (5,20). Second, the participants within our sample were not competitive or elite athletes, which limits the generalizability of our findings to a recreation population, because elite athletes may respond differently to alteration of footwear during CMVJ. Third, only 1 model of each of the footwear groups was tested. Footwear effects reported may only be applicable to the specific shoe models tested in the current study.
Practical Applications
The current findings indicate that men and women respond similarly to wearing minimal and standard training footwear with regard to maximal vertical jump height and lower-limb joint kinetic output. Thus, coaches and athletes may not need to recommend different training footwear for men and women. This study confirms the previous finding that women jump lower than men but provides novel biomechanical evidence that women produce less positive lower-limb joint kinetics but with similar negative lower-limb joint mechanical output than men. It therefore seems that men may have a better ability to use the SSC during maximal vertical jumping. Although more research is needed, this finding may suggest that coaches could develop training programs with a greater focus on rapid eccentric movements in female athletes to optimize SSC utilization during jumping movements. Finally, the slightly smaller ankle- and knee-positive mechanical output in minimal compared with standard footwear may deserve more attention in long-term use of such footwear. The training effects of wearing standard vs. minimal footwear on jumping performance and lower-limb joint involvement in male and female athletes are unclear and remain to be addressed.
Acknowledgments
The authors have no professional relationships with companies or manufacturers that might benefit from the results of the study. There is no financial support for this project, and no funds were received for this study. The results of this study do not constitute endorsement of any product by the authors or the National Strength and Conditioning Association. No funding was provided for this study.
References
1. Alegre LM, Lara AJ, Elvira JL, Aguado X. Muscle morphology and jump performance: Gender and intermuscular variability. J Sports Med Phys Fit 49: 320–326, 2009.
2. Aragón-Vargas LF, Gross MM. Kinesiological factors in vertical jump performance: Differences among individuals. J Appl Biomech 13: 24–44, 1997.
3. Barker LA, Harry JR, Dufek JS, Mercer JA. Aerial rotation effects on vertical jump performance among highly skilled collegiate soccer players. J Strength Cond Res 31: 932–938, 2017.
4. Barnes JL, Schilling BK, Falvo MJ, Weiss LW, Creasy AK, Fry AC. Relationship of jumping and agility performance in female volleyball athletes. J Strength Cond Res 21: 1192–1196, 2007.
5. Blache YA, Beguin A, Monteil K. Effects of various parameters of basketball shoes on vertical jumping performance: A case study/influence des caractéristiques des chaussures de basketball sur la performance en saut vertical: Une étude de cas. Sci Sports 26: 48–50, 2011.
6. Bonacci J, Saunders PU, Hicks A, Rantalainen T, Vicenzino BG, Spratford W. Running in a minimalist and lightweight shoe is not the same as running barefoot: A biomechanical study. Br J Sports Med 47: 387–392, 2013.
7. Caia J, Weiss LW, Chiu LZ, Schilling BK, Paquette MR, Relyea GE. Do lower-body dimensions and body composition explain vertical jump ability? J Strength Cond Res 30: 3073–3083, 2016.
8. Caserotti P, Aagaard P, Simonsen EB, Puggaard L. Contraction-specific differences in maximal muscle power during stretch-shortening cycle movements in elderly males and females. Eur J Appl Physiol 84: 206–212, 2001.
9. Castagna C, Castellini E. Vertical jump performance in Italian male and female national team soccer players. J Strength Cond Res 27: 1156–1161, 2013.
10. de Villarreal ES, Requena B, Cronin JB. The effects of plyometric training on sprint performance: A meta-analysis. J Strength Cond Res 26: 575–584, 2012.
11. de Villiers JE, Venter RE. Barefoot training improved ankle stability and agility in netball players. Int J Sports Coa 9: 485–496, 2014.
12. Esculier J, Dubois B, Dionne CE, Leblond J, Roy J. A consensus definition and rating scale for minimalist shoes. J Foot Ankle Res 8: 42, 2015.
13. Fukashiro S, Komi P. Joint moment and mechanical power flow of the lower limb during vertical jump. Int J Sports Med 8: S15–S21, 1987.
14. Fuller JT, Buckley JD, Tsiros MD, Brown NA, Thewlis D. Redistribution of mechanical work at the knee and ankle joints during fast running in minimalist shoes. J Athl Train 51: 806–812, 2016.
15. Goss DL, Gross MT. Relationships among self-reported shoe type, footstrike pattern, and injury incidence. US Army Med Dep J Oct-Dec: 25–30, 2012.
16. Harry JR, Paquette MR, Caia J, Townsend RJ, Weiss LW, Schilling BK. Effects of footwear condition on maximal jumping performance. J Strength Cond Res 29: 1657–1665, 2015.
17. Harry JR, Paquette MR, Schilling BK, Barker LA, James CR, Dufek JS. Kinetic and electromyographic sub-phase characteristics with relation to countermovement vertical jump performance. J Appl Biomech 34: 291–297, 2018.
18. Hopkins WG. A new view of statistics: A scale of magnitudes for effect statistics. 2017. Available at:
http://www.sportsci.org/resource/stats/effectmag.html. Accessed June 15, 2017.
19. Hubley C, Wells R. A work-energy approach to determine individual joint contributions to vertical jump performance. Eur J Appl Physiol Occup Physiol 50: 247–254, 1983.
20. Laporta JW, Brown LE, Coburn JW, Galpin AJ, Tufano JJ, Cavas VL, et al. Effects of different footwear on vertical jump and landing parameters. J Strength Cond Res 27: 733–737, 2013.
21. Lees A, Vanrenterghem J, De Clercq D. Understanding how an arm swing enhances performance in the vertical jump. J Biomech 37: 1929–1940, 2004.
22. Marquez G, Alegre LM, Jaen D, Martin-Casado L, Aguado X. Sex differences in kinetic and neuromuscular control during jumping and landing. J Musculoskelet Neuronal 17: 409–416, 2017.
23. Miller AE, MacDougall JD, Tarnopolsky MA, Sale DG. Gender differences in strength and muscle fiber characteristics. Eur J Appl Physiol O 66: 254–262, 1993.
24. Paquette MR, Zhang S, Baumgartner LD. Acute effects of barefoot, minimal shoes and running shoes on lower limb mechanics in rear and forefoot strike runners. Footwear Sci 5: 9–18, 2013.
25. Quatman CE, Ford KR, Myer GD, Hewett TE. Maturation leads to gender differences in landing force and vertical jump performance. Am J Sports Med 34: 806–813, 2006.
26. Rice PE, Goodman CL, Capps CR, Triplett NT, Erickson TM, McBride JM. Force– and power–time curve comparison during jumping between strength-matched male and female basketball players. Eur J Sport Sci 17: 286–293, 2017.
27. Sandbakk Ø, Solli GS, Holmberg H. Sex differences in world record performance: The influence of sport discipline and competition duration. Int J Sports Physiol 13: 2–8, 2018.
28. Stephens TM, Lawson BR, Reiser RF. Bilateral asymmetries in max effort single-leg vertical jumps. Biomed Sci Instrum 41: 317–322, 2005.
29. Weinhandl JT, O'Connor KM. Assessment of a greater trochanter-based method of locating the hip joint center. J Biomech 43: 2633–2636, 2010.
30. Woods JJ, Bigland-Ritchie B. Linear and non-linear surface EMG/force relationships in human muscles. An anatomical/functional argument for the existence of both. Am J Phys Med 62: 287–299, 1983.
