- Email: [email protected]
Shod landing provides enhanced energy dissipation at the knee joint relative to barefoot landing from different heights
The Knee 18 (2011) 407–411
Contents lists available at ScienceDirect
The Knee
Shod landing provides enhanced energy dissipation at the knee joint relative to barefoot landing from different heights C.H. Yeow a,b, P.V.S. Lee c,d, J.C.H. Goh a,b,⁎ a
Department of Orthopaedic Surgery, National University of Singapore, Singapore Division of Bioengineering, National University of Singapore, Singapore Department of Mechanical Engineering, University of Melbourne, Australia d Biomechanics Lab, Defence Medical and Environmental Research Institute, Singapore b c
a r t i c l e
i n f o
Article history: Received 31 March 2010 Received in revised form 22 July 2010 Accepted 25 July 2010 Keywords: Energy dissipation Shod landing Kinetics, kinematics and energetics Joint power and eccentric work Landing impact
a b s t r a c t Athletic shoes can directly provide shock absorption at the foot due to its cushioning properties, however it remains unclear how these shoes may affect the level of energy dissipation contributed by the knee joint. This study sought to investigate biomechanical differences, in terms of knee kinematics, kinetics and energetics, between barefoot and shod landing from different heights. Twelve healthy male recreational athletes were recruited and instructed to perform double-leg landing from 0.3-m and 0.6-m heights in barefoot and shod conditions. The shoe model tested was Brooks Maximus II. Markers were placed on the subjects based on the Plug-in Gait Marker Set. Force-plates and motion-capture system were used to capture ground reaction force (GRF) and kinematics data respectively. 2 × 2-ANOVA (barefoot/shod condition × landing height) was performed to examine differences in knee kinematics, kinetics and energetics between barefoot and shod conditions from different landing heights. Peak GRF was not significantly different (p = 0.732–0.824) between barefoot and shod conditions for both landing heights. Knee range-of-motion, flexion angular velocity, external knee flexion moment, and joint power and work were higher during shod landing (p b 0.001 to p = 0.007), compared to barefoot landing for both landing heights. No significant interactions (p = 0.073–0.933) were found between landing height and barefoot/shod condition for the tested parameters. While the increase in landing height can elevate knee energetics independent of barefoot/shod conditions, we have also shown that the shod condition was able to augment the level of energy dissipation contributed by the knee joint, via the knee extensors, regardless of the tested landing heights. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The ability of shoes in enhancing athletic performance has been suggested to be partly attributed to the elastic energy storage and recovery in its cushioning system [1,2]. The athletic shoe wear is usually composed of soft compressible support surface interfaces designed to protect against injuries occurring in sports due to large ground reaction forces (GRF); however, the impact remains high with the use of shoe wear as the athletes actively seek to transform the soft interface into a thinner-stiff form associated with improved stability [3]. Chiu and Shiang [4] further demonstrated that insoles play an important role in the cushioning properties of sport shoes by absorbing up to 32% of impact energy under low impact energy condition. These studies collectively indicated that athletic shoes can contribute to shock absorption and attenuate injury risk during sports through its cushioning system. ⁎ Corresponding author. Department of Orthopaedic Surgery, NUS Tissue Engineering Programme, Office of Life Sciences, National University of Singapore, 27 Medical Drive, Singapore 117510, Singapore. Tel.: +65 6516 5259; fax: +65 6776 5322. E-mail address: [email protected] (J.C.H. Goh). 0968-0160/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2010.07.011
A previous epidemiological study by Hootman et al. [5] reported that barefoot sports such as gymnastics displayed a high incidence rate of knee injuries, like anterior cruciate ligament (ACL) injuries, as compared to shod sports including volleyball and basketball. Moreover, Baitch [6] documented that barefoot dancers sustained a higher injury rate (65%), relative to that of dancers wearing shoes (49%). In addition, although beach volleyball involves barefoot landing on soft sand surfaces, there is a notable risk of acute and overuse knee injuries, which is comparable to that of indoor volleyball [7,8]. In view of the injury risk implicated with barefoot landing during sporting activities, it is important to understand how the kinematics, kinetics and energetics of barefoot landing differ from that of shod landing. Most previous studies examined the biomechanical differences, in terms of kinematics and kinetics, between barefoot and shod running. For instance, Divert et al. [9] reported that barefoot running delivered lower contact and flight time, and lower peak GRF than shod running, which could be attributed to a neural–mechanical adaptation mechanism to reduce the high impact stress sustained during repetitive steps. A more recent study by Squadrone and Hallozzi [10] demonstrated that athletes landed in more ankle plantar flexion during barefoot running than shod running, which resulted in
408
C.H. Yeow et al. / The Knee 18 (2011) 407–411
reduced impact forces and changes in stride kinematics. With relevance to landing, Webster et al. [11] found that barefoot landing can significantly reduce peak knee flexion angles and moments, especially for the limb that underwent ACL reconstruction. Apart from kinematics and kinetics, prior studies have reported on energetics parameters, particularly joint power and work, in order to describe the energy dissipation at the lower extremities during landing [12–14]. Landing results in the application of forces and moments to the lower extremities, which accelerate joint flexion motions and lead to a tendency of the extremities to collapse. A stable landing would require counter extensor moments at the lower extremity joints in order to resist collapse and reduce body velocity to zero without injury. These joint extensor muscles provide eccentric work by absorbing kinetic energy from the skeletal system and stabilizing the landing [13]. An energetics study by Zhang et al. [14] demonstrated that the knee extensors were the major energy dissipaters for different landing heights (0.32-m, 0.62-m and 1.03-m) and different landing techniques (soft, normal and stiff). Moreover, Decker et al. [12] further reported that the knee was the primary shock absorber, among the lower extremity joints, for both genders during landing. While there are preceding investigations of the shod condition on joint kinematics and kinetics, it is still unclear how the shod condition may affect the level of energy dissipation contributed by the knee joint during landing, which may be vital for understanding how athletic shoes can indirectly influence shock absorption at the knee joint during impact maneuvers. The objective of our study was to investigate the biomechanical differences, in terms of knee kinematics, kinetics and energetics, between barefoot and shod landing from different heights. The use of different heights was necessary to understand whether a difference in landing height would influence the effect of the shod condition on the level of energy dissipation contributed by the knee joint during landing. We hypothesized that shod landing can promote the level of energy dissipation contributed by the knee joint, through greater knee flexion range-of-motion (ROM), flexion angular velocity, external flexion moment, and joint power and work, as compared to barefoot landing from the tested landing heights. 2. Methods
and the motion-capture system were calibrated based on the manufacturers’ recommendations and then synchronized via MX UltraNet HD using a GigaBit Ethernet connection. For the barefoot condition, fifteen retroreflective markers (25-mm diameter) were attached to the subject's lower body, according to the Plug-in-Gait Marker Set, specifically on the sacrum and bilaterally on the anterior superior iliac spine, lateral thigh, lateral femoral epicondyle, lateral shank, lateral malleolus, second metatarsal head and calcaneus (Fig. 1). The same marker placement was adopted for the shod condition, except that the calcaneus and second metatarsal head markers were placed on the shoe, rather than on the foot. 2.3. Landing protocol The subjects were instructed to perform a double-leg drop landing maneuver by stepping off a height-adjustable platform with the dominant limb (preferred limb for kicking a ball) and landing with each foot/shoe on each force-plate. They were asked to utilize their natural landing style. The double-leg landing maneuvers were executed from 0.3-m and 0.6-m heights. These heights were similar to landing heights that were commonly adopted in previous reports [12–15]. At each height, the subjects were given 3 min of practice and 5 min of rest before conducting the actual landing trials, and another 5 min of rest prior to the trials for the next landing height. For all subjects, the barefoot and shod landing trials were performed in random sequence. A trial is taken as successful when the subject steps off the platform (without an upward and/or forward jump action) and adopts a stable landing posture. The motion of upward and/or forward jump action was determined from the plot of the average z-coordinate (vertical axis) and x-coordinate (anterior-posterior axis) of the three pelvic markers (left and right anterior superior iliac spine markers, and sacrum marker) against time. We defined an increase in zcoordinate, during step-off, by more than 10 mm with respect to an initial standing position as an upward jump action. Upon landing, if the x-coordinate exceeds 450 mm (75% of the 600-mm distance between the far-edge of the force-plate and edge of the platform) with respect to the initial standing position, we would assume a forward jump action during step-off. For each subject, average data from five successful drop landing trials at each landing height and barefoot/shod condition, were used for analysis.
2.1. Subjects and shoe model Twelve healthy male recreational athletes (age: 23.1 ± 0.8 years, mass: 63.7 ± 6.3 kg, and height: 1.73 ± 0.05 m) were recruited from the local university. Subject exclusion criterion was a history of lower extremity injuries/diseases that might affect landing biomechanics. All subjects signed informed consent forms prior to their participation in accordance with the university's Institutional Review Board. Anthropometric data, such as height, weight, knee width, ankle width, leg length and inter-anterior superior iliac spine distance were acquired from all subjects. The subjects wore the same shoe model (Maximus II, Brooks Sports Inc., WA) and were fitted according to their foot size. The Brooks Maximus II shoe is a cross trainer, which features forefoot and rearfoot hydroflow cushioning for comfort and protection of the heel and forefoot from shock. 2.2. Instrumentation setup The study was conducted at the Motion Analysis Laboratory, Department of Orthopaedic Surgery, National University Hospital, Singapore. Two force-plates (Kistler, Winterthur, Switzerland), embedded into the floor, were used to obtain GRF data while a motion-capture system (Vicon MX, Oxford Metrics, UK) with six infrared cameras was used to obtain kinematics data. GRF and kinematics data were collected at sampling rates of 1000 Hz and 250 Hz respectively. Prior to the start of landing trials, the force-plates
Fig. 1. Plug-in-Gait Marker Set. [1 — sacrum; 2, 3 — anterior superior iliac spine; 4, 5 — lateral thigh; 6, 7 — lateral femoral epicondyle; 8, 9 — lateral shank; 10, 11 — lateral malleolus, 12, 13 — second metatarsal head; 14, 15 — calcaneus].
C.H. Yeow et al. / The Knee 18 (2011) 407–411
2.4. Data collection and analysis
409
3. Results 3.1. Main effects of barefoot/shod conditions
The motion analysis software used were Vicon Workstation 5.1 and Polygon 3.1, whereby only the data for the dominant limb was analyzed. Knee kinematics data was smoothed using a Woltring filter with a mean squared error of 20 mm2 [16]. External knee flexion moment was determined using inverse dynamics. Knee joint power was calculated as the product of the internal knee joint moment and knee flexion angular velocity (rate of change of knee flexion angle with time). Knee joint work was computed as joint power integrated over time; negative work values represent energy absorption via eccentric muscular contractions of the knee extensors [13,17]. For the barefoot condition, GRF was normalized to body weight (BW) while external knee joint moment, power and work were normalized to body mass. As for the shod condition, the mass/weight of the shoes was included in the normalization. The GRF, knee flexion angle, knee flexion angular velocity, external knee flexion moment, and knee joint power and work were obtained from the landing phase of the dominant limb (Fig. 2), which was defined as the time between initial contact and peak knee flexion. Knee ROM was taken as the change in knee flexion angle between the start and end of the landing phase.
2.5. Statistical testing Statistical analysis was conducted using SigmaStat 3.5 (SysTat Software Inc., USA). We performed a two-way-ANOVA (barefoot/shod condition × landing height) with post-hoc Bonferroni pair-wise comparisons to examine the differences in GRF, knee ROM, knee flexion angular velocity, external knee flexion moment, and joint power and work during the landing phase between different landing heights, and between barefoot/shod conditions. All significance levels were set at p=0.05.
Peak vertical GRF was not found to be significantly different (0.3-m: p = 0.824; 0.6-m: p = 0.732) between barefoot/shod conditions (Fig. 3A). Moreover, the peak external knee flexion moment was considerably elevated (0.3-m: p = 0.013; 0.6-m: p = 0.030) during shod landing, relative to barefoot landing (Fig. 3B). The knee ROM was also substantially higher during shod landing (0.3-m: p = 0.006; 0.6-m: p b 0.001) compared to barefoot landing (Fig. 4A). Similar observations were noted for the peak knee flexion angular velocity, whereby the angular velocity was markedly increased (0.3-m: p = 0.007; 0.6-m: p b 0.001) during shod landing compared to barefoot landing (Fig. 4B). In terms of energetics, the peak (negative) knee joint power was greater (0.3-m: p = 0.003; 0.6-m: p b 0.001) during shod landing, relative to barefoot landing (Fig. 5A). Additionally, the knee joint demonstrated larger eccentric work (0.3-m: p b 0.001; 0.6-m: p = 0.002) during shod landing, relative to barefoot landing (Fig. 5B).
3.2. Main effects of landing height Peak vertical GRF was not found to be significantly different (barefoot: p = 0.104; shod: p = 0.082) between landing heights (Fig. 3A). The knee moment was greater (barefoot: p = 0.002; shod: p = 0.005) at 0.6-m height than at 0.3-m height (Fig. 3B). The knee ROM was also found to be greater (barefoot: p = 0.025; shod: p = 0.004) at 0.6-m height than at 0.3-m height (Fig. 4A). Furthermore, the peak knee flexion angular velocity was observed to be larger (barefoot: p = 0.008; shod: p b 0.001) at 0.6-m height than at 0.3-m height (Fig. 4B). For energetics, the peak joint power was significantly higher (barefoot: p b 0.001; shod: p b 0.001) at 0.6-m height than at 0.3-m height (Fig. 5A). The knee joint further displayed elevated eccentric work (barefoot: p b 0.001; shod: p = 0.002) at 0.6-m height than at 0.3-m height (Fig. 5B).
3.3. Interactions There were no statistically significant interactions (p = 0.073–0.933) between landing height and barefoot/shod condition for the tested parameters, indicating that the different levels of landing height did not influence the effects of the shoe model.
Fig. 2. Representative profiles for vertical GRF, external knee flexion moment, knee flexion angle, knee flexion angular velocity and knee joint power during landing phase of a subject performing landing from a 0.6-m height.
410
C.H. Yeow et al. / The Knee 18 (2011) 407–411
Fig. 3. Comparison of (A) peak vertical GRF and (B) external knee flexion moment between barefoot and shod landing, and between 0.3-m and 0.6-m heights. *Significant difference (p b 0.05) compared to barefoot landing. #Significant difference (p b 0.05) compared to 0.3-m height.
Fig. 5. Comparison of (A) peak knee joint power and (B) eccentric work between barefoot and shod landing, and between 0.3-m and 0.6-m heights. *Significant difference (p b 0.05) compared to barefoot landing. #Significant difference (p b 0.05) compared to 0.3-m height.
4. Discussion
Fig. 4. Comparison of (A) knee ROM and (B) peak knee flexion angular velocity between barefoot and shod landing, and between 0.3-m and 0.6-m heights. *Significant difference (p b 0.05) compared to barefoot landing. #Significant difference (p b 0.05) compared to 0.3-m height.
In view of the prior studies that examined the effect of athletic shoes on running and landing biomechanics, it remains unclear how shod landing may affect the level of energy dissipation contributed by the knee joint. The aim of our study was to investigate the biomechanical differences, in terms of knee kinematics, kinetics and energetics, between barefoot and shod landing from different heights. The principal findings of this study were: 1) shod landing induced greater peak external knee flexion moment, 2) the knee joint exhibited larger knee ROM and peak knee flexion angular velocity during shod landing relative to barefoot landing, and 3) the shod condition increased the knee joint power and work during landing. Although prior studies on shod running reported a higher GRF compared to barefoot running [9,10], we did not observe any difference in GRF between barefoot and shod landing in the current study. This lack of difference was consistent with a previous barefoot/shod landing study conducted by Webster et al. [11]. A recent report by Yeow et al. [18] illustrated that the knee joint tends to respond, with greater flexion, to a larger landing impact from an elevated height during double-leg landing. This response was suggested as a means to enhance shock absorption and minimize lower extremity injury risk. Moreover, the presence of high GRF during landing in a less flexed knee position was suggested to be a contributing factor in non-contact ACL injuries [19,20]. Lim et al. [21] indicated that training athletes to land with larger knee flexion is necessary to reduce the risk of ACL failure due to high landing impact. In our study, we observed a substantial increase in knee ROM during shod landing, which implied that the knee joint is able to respond more effectively, in terms of knee flexion, against the peak GRF in the shod condition. We further noted an elevated knee flexion angular velocity during shod landing as compared to barefoot landing. This increased active knee flexion may further contribute to the mitigation of landing impact [22,23]. The presence of high knee ROM and angular velocity noted for the shod condition in our study may have contributed
C.H. Yeow et al. / The Knee 18 (2011) 407–411
to an attenuated landing impact, which may explain why we did not observe a higher GRF in the shod condition, relative to the barefoot condition, as reported in previous running studies. In comparison to the findings reported by Webster et al. [11], we also found a higher peak knee flexion moment during shod landing, relative to barefoot landing. This effect was observed at both landing heights and was likely attributed to the peak GRF and the increased moment arm, due to greater knee flexion, during shod landing. This increased tendency to flex was mainly countered by the knee extensors, which implied that these muscles may be working harder during shod landing. Most importantly, both the peak knee joint power and work were considerably higher during shod landing compared to barefoot landing. Moreover, these parameters were also markedly elevated at the 0.6-m height relative to the 0.3-height for both types of landing. Zhang et al. [14] have previously demonstrated that knee joint power and work can increase with landing height, with the knee extensors playing the dominant role in energy absorption. Nonetheless, in our study, we have not only verified that the elevation in landing height can enhance knee energetics regardless of the barefoot or shod condition, we have also illustrated that the shod condition can augment knee energetics regardless of landing height. We acknowledge that there might be inter-subject dissimilarities in landing style. As our emphasis was to investigate the effects of the shod condition on knee kinematics, kinetics and energetics for recreational athletes with varying landing experiences, the subjects were asked to adopt their natural landing styles [12,14,15], rather than to follow an instructed standardized landing style. We expect that a standardized landing style may be relatively more germane for studies on competitive athletes, such as basketball and volleyball players, who possess similar abilities in learning landing maneuvers or prior experiences in landing execution. Another limitation of this study was that only male subjects were tested. Prior reports have observed gender differences in knee joint kinematics and muscle activities during landing which can contribute to the susceptibility towards ACL injuries [24,25]. Hence, future studies should examine whether female subjects would respond differently, relative to male subjects, in terms of knee kinematics, kinetics and energetics when experiencing shod and barefoot landing conditions. Understanding of these differences could provide insights towards the development of appropriate shoe wear that can effectively reduce the lower extremity injury risk for the female gender. Collectively, our results demonstrated that shod landing can increase the knee ROM, flexion angular velocity, external flexion moment, and joint power and work from the two tested heights, relative to barefoot landing. While we have indicated that the increase in landing height can elevate knee energetics independent of barefoot/ shod conditions, we have also shown that the shod condition was able to augment the level of energy dissipation contributed by the knee joint, via the knee extensors, regardless of the tested landing heights. Therefore, besides being able to directly provide shock absorption at the foot due to its cushioning properties, the shod condition can also indirectly contribute to impact energy dissipation through the knee joint during landing maneuvers. The clinical relevance of this study would be that landing on hard surfaces from various heights should be conducted in the shod condition so as to permit improved shock absorption by the musculature through increased flexion and reduced stiffness at the knee joint, relative to that of the barefoot condition. This effect may in turn mitigate the amount of mechanical energy absorbed by passive anatomical structures and therefore reduce the risk of sustaining lower extremity injuries, such as stress fractures and ACL ruptures [26–29]. 5. Conflict of Interest We declare that there are no direct or indirect financial interests involved with thecontent of this paper. The main source of grant
411
support for the project is theAcademic Research Fund (National University of Singapore).
Acknowledgement This work was funded by the Academic Research Fund, National University of Singapore.
References [1] Shorten MR. The energetics of running and running shoes. J Biomech 1993;26: 41–51. [2] Stefanyshyn DJ, Nigg BM. Energy aspects associated with sport shoes. Sportverletz Sportschaden 2000;14:82–9. [3] Robbins S, Waked E. Balance and vertical impact in sports: role of shoe sole materials. Arch Phys Med Rehabil 1997;78:463–7. [4] Chiu HT, Shiang TY. Effects of insoles and additional shock absorption foam on the cushioning properties of sport shoes. J Appl Biomech 2007;23:119–27. [5] Hootman JM, Dick R, Agel J. Epidemiology of collegiate injuries for 15 sports: summary and recommendations for injury prevention initiatives. J Athl Train 2007;42:311. [6] Baitch SP. A biomechanical approach to aerobic dance injuries. In: Solomon R, Solomon J, Minton SC, editors. Preventing dance injuries. Illinois: Human Kinetics; 2005. p. 56. [7] Aagaard H, Scavenius M, Jørgensen U. An epidemiological analysis of the injury pattern in indoor and in beach volleyball. Int J Sports Med 1997;18:217. [8] Reeser JC, Verhagen E, Briner WW, Askeland TI, Bahr R. Strategies for the prevention of volleyball related injuries. Br J Sports Med 2006;40:594. [9] Divert C, Mornieux G, Baur H, Mayer F, Belli A. Mechanical comparison of barefoot and shod running. Int J Sports Med 2005;26:593–8. [10] Squadrone R, Gallozzi C. Biomechanical and physiological comparison of barefoot and two shod conditions in experienced barefoot runners. J Sports Med Phys Fitness 2009;49:6–13. [11] Webster KE, Kinmont JC, Payne R, Feller JA. Biomechanical differences in landing with and without shoe wear after ACL reconstruction. Clin Biomech (Bristol, Avon) 2004;19:978–81. [12] Decker MJ, Torry MR, Wyland DJ, Sterett WI, Richard Steadman J. Gender differences in lower extremity kinematics, kinetics and energy absorption during landing. Clin Biomech (Bristol, Avon) 2003;18:662–9. [13] DeVita P, Skelly WA. Effect of landing stiffness on joint kinetics and energetics in the lower extremity. Med Sci Sports Exerc 1992;24:108–15. [14] Zhang SN, Bates BT, Dufek JS. Contributions of lower extremity joints to energy dissipation during landings. Med Sci Sports Exerc 2000;32:812–9. [15] McNitt-Gray JL. Kinetics of the lower extremities during drop landings from three heights. J Biomech 1993;26:1037–46. [16] Burnfield JM, Powers CM. The role of center of mass kinematics in predicting peak utilized coefficient of friction during walking. J Forensic Sci 2007;52:1328–33. [17] Winter DA. Biomechanics and motor control of human movement. second ed. New York: Wiley; 1990. [18] Yeow CH, Lee PV, Goh JC. Sagittal knee joint kinematics and energetics in response to different landing heights and techniques. Knee 2010;17:127–31. [19] Hashemi J, Breighner R, Jang TH, Chandrashekar N, Ekwaro-Osire S, Slauterbeck JR. Increasing pre-activation of the quadriceps muscle protects the ACL during the landing phase of a jump: an in vitro simulation. Knee 2010;17:235–41. [20] Podraza JT, White SC. Effect of knee flexion angle on ground reaction forces, knee moments and muscle co-contraction during an impact-like deceleration landing: implications for the non-contact mechanism of ACL injury. Knee 2010;17:291–5. [21] Lim BO, Lee YS, Kim JG, An KO, Yoo J, Kwon Y. Effects of sports injury prevention training on the biomechanical risk factors of ACL injury in high school female basketball players. Am J Sports Med 2009;37:1728–34. [22] Yu B, Lin CF, Garrett WE. Lower extremity biomechanics during the landing of a stop-jump task. Clin Biomech (Bristol, Avon) 2006;21:297–305. [23] Yeow CH, Lee PVS, Goh JCH. Regression relationships of landing height with ground reaction forces, knee flexion angles, angular velocities and joint powers during double-leg landing. Knee 2009;16:381–6. [24] Nagano Y, Ida H, Akai M, Fukubayashi T. Gender differences in knee kinematics and muscle activity during single limb drop landing. Knee 2007;14:218–23. [25] Urabe Y, Kobayashi R, Sumida S, Tanaka K, Yoshida N, Nishiwaki GA, et al. Electromyographic analysis of the knee during jump landing in male and female athletes. Knee 2005;12:129–34. [26] Butler RJ, Crowell III HP, Davis IM. Lower extremity stiffness: implications for performance and injury. Clin Biomech (Bristol, Avon) 2003;18:511–7. [27] Pollard CD, Sigward SM, Powers CM. Limited hip and knee flexion during landing is associated with increased frontal plane knee motion and moments. Clin Biomech (Bristol, Avon) 2010;25:142–6. [28] Prilutsky BI. Eccentric muscle action in sport and exercise. In: Zatsiorsky V, editor. Biomechanics in sport: performance enhancement and injury prevention. Oxford: Blackwell Publishing; 2005. p. 56–86. [29] Williams III DS, Davis IM, Scholz JP, Hamill J, Buchanan TS. High-arched runners exhibit increased leg stiffness compared to low-arched runners. Gait Posture 2004;19:263–9.
Contents lists available at ScienceDirect
The Knee
Shod landing provides enhanced energy dissipation at the knee joint relative to barefoot landing from different heights C.H. Yeow a,b, P.V.S. Lee c,d, J.C.H. Goh a,b,⁎ a
Department of Orthopaedic Surgery, National University of Singapore, Singapore Division of Bioengineering, National University of Singapore, Singapore Department of Mechanical Engineering, University of Melbourne, Australia d Biomechanics Lab, Defence Medical and Environmental Research Institute, Singapore b c
a r t i c l e
i n f o
Article history: Received 31 March 2010 Received in revised form 22 July 2010 Accepted 25 July 2010 Keywords: Energy dissipation Shod landing Kinetics, kinematics and energetics Joint power and eccentric work Landing impact
a b s t r a c t Athletic shoes can directly provide shock absorption at the foot due to its cushioning properties, however it remains unclear how these shoes may affect the level of energy dissipation contributed by the knee joint. This study sought to investigate biomechanical differences, in terms of knee kinematics, kinetics and energetics, between barefoot and shod landing from different heights. Twelve healthy male recreational athletes were recruited and instructed to perform double-leg landing from 0.3-m and 0.6-m heights in barefoot and shod conditions. The shoe model tested was Brooks Maximus II. Markers were placed on the subjects based on the Plug-in Gait Marker Set. Force-plates and motion-capture system were used to capture ground reaction force (GRF) and kinematics data respectively. 2 × 2-ANOVA (barefoot/shod condition × landing height) was performed to examine differences in knee kinematics, kinetics and energetics between barefoot and shod conditions from different landing heights. Peak GRF was not significantly different (p = 0.732–0.824) between barefoot and shod conditions for both landing heights. Knee range-of-motion, flexion angular velocity, external knee flexion moment, and joint power and work were higher during shod landing (p b 0.001 to p = 0.007), compared to barefoot landing for both landing heights. No significant interactions (p = 0.073–0.933) were found between landing height and barefoot/shod condition for the tested parameters. While the increase in landing height can elevate knee energetics independent of barefoot/shod conditions, we have also shown that the shod condition was able to augment the level of energy dissipation contributed by the knee joint, via the knee extensors, regardless of the tested landing heights. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The ability of shoes in enhancing athletic performance has been suggested to be partly attributed to the elastic energy storage and recovery in its cushioning system [1,2]. The athletic shoe wear is usually composed of soft compressible support surface interfaces designed to protect against injuries occurring in sports due to large ground reaction forces (GRF); however, the impact remains high with the use of shoe wear as the athletes actively seek to transform the soft interface into a thinner-stiff form associated with improved stability [3]. Chiu and Shiang [4] further demonstrated that insoles play an important role in the cushioning properties of sport shoes by absorbing up to 32% of impact energy under low impact energy condition. These studies collectively indicated that athletic shoes can contribute to shock absorption and attenuate injury risk during sports through its cushioning system. ⁎ Corresponding author. Department of Orthopaedic Surgery, NUS Tissue Engineering Programme, Office of Life Sciences, National University of Singapore, 27 Medical Drive, Singapore 117510, Singapore. Tel.: +65 6516 5259; fax: +65 6776 5322. E-mail address: [email protected] (J.C.H. Goh). 0968-0160/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2010.07.011
A previous epidemiological study by Hootman et al. [5] reported that barefoot sports such as gymnastics displayed a high incidence rate of knee injuries, like anterior cruciate ligament (ACL) injuries, as compared to shod sports including volleyball and basketball. Moreover, Baitch [6] documented that barefoot dancers sustained a higher injury rate (65%), relative to that of dancers wearing shoes (49%). In addition, although beach volleyball involves barefoot landing on soft sand surfaces, there is a notable risk of acute and overuse knee injuries, which is comparable to that of indoor volleyball [7,8]. In view of the injury risk implicated with barefoot landing during sporting activities, it is important to understand how the kinematics, kinetics and energetics of barefoot landing differ from that of shod landing. Most previous studies examined the biomechanical differences, in terms of kinematics and kinetics, between barefoot and shod running. For instance, Divert et al. [9] reported that barefoot running delivered lower contact and flight time, and lower peak GRF than shod running, which could be attributed to a neural–mechanical adaptation mechanism to reduce the high impact stress sustained during repetitive steps. A more recent study by Squadrone and Hallozzi [10] demonstrated that athletes landed in more ankle plantar flexion during barefoot running than shod running, which resulted in
408
C.H. Yeow et al. / The Knee 18 (2011) 407–411
reduced impact forces and changes in stride kinematics. With relevance to landing, Webster et al. [11] found that barefoot landing can significantly reduce peak knee flexion angles and moments, especially for the limb that underwent ACL reconstruction. Apart from kinematics and kinetics, prior studies have reported on energetics parameters, particularly joint power and work, in order to describe the energy dissipation at the lower extremities during landing [12–14]. Landing results in the application of forces and moments to the lower extremities, which accelerate joint flexion motions and lead to a tendency of the extremities to collapse. A stable landing would require counter extensor moments at the lower extremity joints in order to resist collapse and reduce body velocity to zero without injury. These joint extensor muscles provide eccentric work by absorbing kinetic energy from the skeletal system and stabilizing the landing [13]. An energetics study by Zhang et al. [14] demonstrated that the knee extensors were the major energy dissipaters for different landing heights (0.32-m, 0.62-m and 1.03-m) and different landing techniques (soft, normal and stiff). Moreover, Decker et al. [12] further reported that the knee was the primary shock absorber, among the lower extremity joints, for both genders during landing. While there are preceding investigations of the shod condition on joint kinematics and kinetics, it is still unclear how the shod condition may affect the level of energy dissipation contributed by the knee joint during landing, which may be vital for understanding how athletic shoes can indirectly influence shock absorption at the knee joint during impact maneuvers. The objective of our study was to investigate the biomechanical differences, in terms of knee kinematics, kinetics and energetics, between barefoot and shod landing from different heights. The use of different heights was necessary to understand whether a difference in landing height would influence the effect of the shod condition on the level of energy dissipation contributed by the knee joint during landing. We hypothesized that shod landing can promote the level of energy dissipation contributed by the knee joint, through greater knee flexion range-of-motion (ROM), flexion angular velocity, external flexion moment, and joint power and work, as compared to barefoot landing from the tested landing heights. 2. Methods
and the motion-capture system were calibrated based on the manufacturers’ recommendations and then synchronized via MX UltraNet HD using a GigaBit Ethernet connection. For the barefoot condition, fifteen retroreflective markers (25-mm diameter) were attached to the subject's lower body, according to the Plug-in-Gait Marker Set, specifically on the sacrum and bilaterally on the anterior superior iliac spine, lateral thigh, lateral femoral epicondyle, lateral shank, lateral malleolus, second metatarsal head and calcaneus (Fig. 1). The same marker placement was adopted for the shod condition, except that the calcaneus and second metatarsal head markers were placed on the shoe, rather than on the foot. 2.3. Landing protocol The subjects were instructed to perform a double-leg drop landing maneuver by stepping off a height-adjustable platform with the dominant limb (preferred limb for kicking a ball) and landing with each foot/shoe on each force-plate. They were asked to utilize their natural landing style. The double-leg landing maneuvers were executed from 0.3-m and 0.6-m heights. These heights were similar to landing heights that were commonly adopted in previous reports [12–15]. At each height, the subjects were given 3 min of practice and 5 min of rest before conducting the actual landing trials, and another 5 min of rest prior to the trials for the next landing height. For all subjects, the barefoot and shod landing trials were performed in random sequence. A trial is taken as successful when the subject steps off the platform (without an upward and/or forward jump action) and adopts a stable landing posture. The motion of upward and/or forward jump action was determined from the plot of the average z-coordinate (vertical axis) and x-coordinate (anterior-posterior axis) of the three pelvic markers (left and right anterior superior iliac spine markers, and sacrum marker) against time. We defined an increase in zcoordinate, during step-off, by more than 10 mm with respect to an initial standing position as an upward jump action. Upon landing, if the x-coordinate exceeds 450 mm (75% of the 600-mm distance between the far-edge of the force-plate and edge of the platform) with respect to the initial standing position, we would assume a forward jump action during step-off. For each subject, average data from five successful drop landing trials at each landing height and barefoot/shod condition, were used for analysis.
2.1. Subjects and shoe model Twelve healthy male recreational athletes (age: 23.1 ± 0.8 years, mass: 63.7 ± 6.3 kg, and height: 1.73 ± 0.05 m) were recruited from the local university. Subject exclusion criterion was a history of lower extremity injuries/diseases that might affect landing biomechanics. All subjects signed informed consent forms prior to their participation in accordance with the university's Institutional Review Board. Anthropometric data, such as height, weight, knee width, ankle width, leg length and inter-anterior superior iliac spine distance were acquired from all subjects. The subjects wore the same shoe model (Maximus II, Brooks Sports Inc., WA) and were fitted according to their foot size. The Brooks Maximus II shoe is a cross trainer, which features forefoot and rearfoot hydroflow cushioning for comfort and protection of the heel and forefoot from shock. 2.2. Instrumentation setup The study was conducted at the Motion Analysis Laboratory, Department of Orthopaedic Surgery, National University Hospital, Singapore. Two force-plates (Kistler, Winterthur, Switzerland), embedded into the floor, were used to obtain GRF data while a motion-capture system (Vicon MX, Oxford Metrics, UK) with six infrared cameras was used to obtain kinematics data. GRF and kinematics data were collected at sampling rates of 1000 Hz and 250 Hz respectively. Prior to the start of landing trials, the force-plates
Fig. 1. Plug-in-Gait Marker Set. [1 — sacrum; 2, 3 — anterior superior iliac spine; 4, 5 — lateral thigh; 6, 7 — lateral femoral epicondyle; 8, 9 — lateral shank; 10, 11 — lateral malleolus, 12, 13 — second metatarsal head; 14, 15 — calcaneus].
C.H. Yeow et al. / The Knee 18 (2011) 407–411
2.4. Data collection and analysis
409
3. Results 3.1. Main effects of barefoot/shod conditions
The motion analysis software used were Vicon Workstation 5.1 and Polygon 3.1, whereby only the data for the dominant limb was analyzed. Knee kinematics data was smoothed using a Woltring filter with a mean squared error of 20 mm2 [16]. External knee flexion moment was determined using inverse dynamics. Knee joint power was calculated as the product of the internal knee joint moment and knee flexion angular velocity (rate of change of knee flexion angle with time). Knee joint work was computed as joint power integrated over time; negative work values represent energy absorption via eccentric muscular contractions of the knee extensors [13,17]. For the barefoot condition, GRF was normalized to body weight (BW) while external knee joint moment, power and work were normalized to body mass. As for the shod condition, the mass/weight of the shoes was included in the normalization. The GRF, knee flexion angle, knee flexion angular velocity, external knee flexion moment, and knee joint power and work were obtained from the landing phase of the dominant limb (Fig. 2), which was defined as the time between initial contact and peak knee flexion. Knee ROM was taken as the change in knee flexion angle between the start and end of the landing phase.
2.5. Statistical testing Statistical analysis was conducted using SigmaStat 3.5 (SysTat Software Inc., USA). We performed a two-way-ANOVA (barefoot/shod condition × landing height) with post-hoc Bonferroni pair-wise comparisons to examine the differences in GRF, knee ROM, knee flexion angular velocity, external knee flexion moment, and joint power and work during the landing phase between different landing heights, and between barefoot/shod conditions. All significance levels were set at p=0.05.
Peak vertical GRF was not found to be significantly different (0.3-m: p = 0.824; 0.6-m: p = 0.732) between barefoot/shod conditions (Fig. 3A). Moreover, the peak external knee flexion moment was considerably elevated (0.3-m: p = 0.013; 0.6-m: p = 0.030) during shod landing, relative to barefoot landing (Fig. 3B). The knee ROM was also substantially higher during shod landing (0.3-m: p = 0.006; 0.6-m: p b 0.001) compared to barefoot landing (Fig. 4A). Similar observations were noted for the peak knee flexion angular velocity, whereby the angular velocity was markedly increased (0.3-m: p = 0.007; 0.6-m: p b 0.001) during shod landing compared to barefoot landing (Fig. 4B). In terms of energetics, the peak (negative) knee joint power was greater (0.3-m: p = 0.003; 0.6-m: p b 0.001) during shod landing, relative to barefoot landing (Fig. 5A). Additionally, the knee joint demonstrated larger eccentric work (0.3-m: p b 0.001; 0.6-m: p = 0.002) during shod landing, relative to barefoot landing (Fig. 5B).
3.2. Main effects of landing height Peak vertical GRF was not found to be significantly different (barefoot: p = 0.104; shod: p = 0.082) between landing heights (Fig. 3A). The knee moment was greater (barefoot: p = 0.002; shod: p = 0.005) at 0.6-m height than at 0.3-m height (Fig. 3B). The knee ROM was also found to be greater (barefoot: p = 0.025; shod: p = 0.004) at 0.6-m height than at 0.3-m height (Fig. 4A). Furthermore, the peak knee flexion angular velocity was observed to be larger (barefoot: p = 0.008; shod: p b 0.001) at 0.6-m height than at 0.3-m height (Fig. 4B). For energetics, the peak joint power was significantly higher (barefoot: p b 0.001; shod: p b 0.001) at 0.6-m height than at 0.3-m height (Fig. 5A). The knee joint further displayed elevated eccentric work (barefoot: p b 0.001; shod: p = 0.002) at 0.6-m height than at 0.3-m height (Fig. 5B).
3.3. Interactions There were no statistically significant interactions (p = 0.073–0.933) between landing height and barefoot/shod condition for the tested parameters, indicating that the different levels of landing height did not influence the effects of the shoe model.
Fig. 2. Representative profiles for vertical GRF, external knee flexion moment, knee flexion angle, knee flexion angular velocity and knee joint power during landing phase of a subject performing landing from a 0.6-m height.
410
C.H. Yeow et al. / The Knee 18 (2011) 407–411
Fig. 3. Comparison of (A) peak vertical GRF and (B) external knee flexion moment between barefoot and shod landing, and between 0.3-m and 0.6-m heights. *Significant difference (p b 0.05) compared to barefoot landing. #Significant difference (p b 0.05) compared to 0.3-m height.
Fig. 5. Comparison of (A) peak knee joint power and (B) eccentric work between barefoot and shod landing, and between 0.3-m and 0.6-m heights. *Significant difference (p b 0.05) compared to barefoot landing. #Significant difference (p b 0.05) compared to 0.3-m height.
4. Discussion
Fig. 4. Comparison of (A) knee ROM and (B) peak knee flexion angular velocity between barefoot and shod landing, and between 0.3-m and 0.6-m heights. *Significant difference (p b 0.05) compared to barefoot landing. #Significant difference (p b 0.05) compared to 0.3-m height.
In view of the prior studies that examined the effect of athletic shoes on running and landing biomechanics, it remains unclear how shod landing may affect the level of energy dissipation contributed by the knee joint. The aim of our study was to investigate the biomechanical differences, in terms of knee kinematics, kinetics and energetics, between barefoot and shod landing from different heights. The principal findings of this study were: 1) shod landing induced greater peak external knee flexion moment, 2) the knee joint exhibited larger knee ROM and peak knee flexion angular velocity during shod landing relative to barefoot landing, and 3) the shod condition increased the knee joint power and work during landing. Although prior studies on shod running reported a higher GRF compared to barefoot running [9,10], we did not observe any difference in GRF between barefoot and shod landing in the current study. This lack of difference was consistent with a previous barefoot/shod landing study conducted by Webster et al. [11]. A recent report by Yeow et al. [18] illustrated that the knee joint tends to respond, with greater flexion, to a larger landing impact from an elevated height during double-leg landing. This response was suggested as a means to enhance shock absorption and minimize lower extremity injury risk. Moreover, the presence of high GRF during landing in a less flexed knee position was suggested to be a contributing factor in non-contact ACL injuries [19,20]. Lim et al. [21] indicated that training athletes to land with larger knee flexion is necessary to reduce the risk of ACL failure due to high landing impact. In our study, we observed a substantial increase in knee ROM during shod landing, which implied that the knee joint is able to respond more effectively, in terms of knee flexion, against the peak GRF in the shod condition. We further noted an elevated knee flexion angular velocity during shod landing as compared to barefoot landing. This increased active knee flexion may further contribute to the mitigation of landing impact [22,23]. The presence of high knee ROM and angular velocity noted for the shod condition in our study may have contributed
C.H. Yeow et al. / The Knee 18 (2011) 407–411
to an attenuated landing impact, which may explain why we did not observe a higher GRF in the shod condition, relative to the barefoot condition, as reported in previous running studies. In comparison to the findings reported by Webster et al. [11], we also found a higher peak knee flexion moment during shod landing, relative to barefoot landing. This effect was observed at both landing heights and was likely attributed to the peak GRF and the increased moment arm, due to greater knee flexion, during shod landing. This increased tendency to flex was mainly countered by the knee extensors, which implied that these muscles may be working harder during shod landing. Most importantly, both the peak knee joint power and work were considerably higher during shod landing compared to barefoot landing. Moreover, these parameters were also markedly elevated at the 0.6-m height relative to the 0.3-height for both types of landing. Zhang et al. [14] have previously demonstrated that knee joint power and work can increase with landing height, with the knee extensors playing the dominant role in energy absorption. Nonetheless, in our study, we have not only verified that the elevation in landing height can enhance knee energetics regardless of the barefoot or shod condition, we have also illustrated that the shod condition can augment knee energetics regardless of landing height. We acknowledge that there might be inter-subject dissimilarities in landing style. As our emphasis was to investigate the effects of the shod condition on knee kinematics, kinetics and energetics for recreational athletes with varying landing experiences, the subjects were asked to adopt their natural landing styles [12,14,15], rather than to follow an instructed standardized landing style. We expect that a standardized landing style may be relatively more germane for studies on competitive athletes, such as basketball and volleyball players, who possess similar abilities in learning landing maneuvers or prior experiences in landing execution. Another limitation of this study was that only male subjects were tested. Prior reports have observed gender differences in knee joint kinematics and muscle activities during landing which can contribute to the susceptibility towards ACL injuries [24,25]. Hence, future studies should examine whether female subjects would respond differently, relative to male subjects, in terms of knee kinematics, kinetics and energetics when experiencing shod and barefoot landing conditions. Understanding of these differences could provide insights towards the development of appropriate shoe wear that can effectively reduce the lower extremity injury risk for the female gender. Collectively, our results demonstrated that shod landing can increase the knee ROM, flexion angular velocity, external flexion moment, and joint power and work from the two tested heights, relative to barefoot landing. While we have indicated that the increase in landing height can elevate knee energetics independent of barefoot/ shod conditions, we have also shown that the shod condition was able to augment the level of energy dissipation contributed by the knee joint, via the knee extensors, regardless of the tested landing heights. Therefore, besides being able to directly provide shock absorption at the foot due to its cushioning properties, the shod condition can also indirectly contribute to impact energy dissipation through the knee joint during landing maneuvers. The clinical relevance of this study would be that landing on hard surfaces from various heights should be conducted in the shod condition so as to permit improved shock absorption by the musculature through increased flexion and reduced stiffness at the knee joint, relative to that of the barefoot condition. This effect may in turn mitigate the amount of mechanical energy absorbed by passive anatomical structures and therefore reduce the risk of sustaining lower extremity injuries, such as stress fractures and ACL ruptures [26–29]. 5. Conflict of Interest We declare that there are no direct or indirect financial interests involved with thecontent of this paper. The main source of grant
411
support for the project is theAcademic Research Fund (National University of Singapore).
Acknowledgement This work was funded by the Academic Research Fund, National University of Singapore.
References [1] Shorten MR. The energetics of running and running shoes. J Biomech 1993;26: 41–51. [2] Stefanyshyn DJ, Nigg BM. Energy aspects associated with sport shoes. Sportverletz Sportschaden 2000;14:82–9. [3] Robbins S, Waked E. Balance and vertical impact in sports: role of shoe sole materials. Arch Phys Med Rehabil 1997;78:463–7. [4] Chiu HT, Shiang TY. Effects of insoles and additional shock absorption foam on the cushioning properties of sport shoes. J Appl Biomech 2007;23:119–27. [5] Hootman JM, Dick R, Agel J. Epidemiology of collegiate injuries for 15 sports: summary and recommendations for injury prevention initiatives. J Athl Train 2007;42:311. [6] Baitch SP. A biomechanical approach to aerobic dance injuries. In: Solomon R, Solomon J, Minton SC, editors. Preventing dance injuries. Illinois: Human Kinetics; 2005. p. 56. [7] Aagaard H, Scavenius M, Jørgensen U. An epidemiological analysis of the injury pattern in indoor and in beach volleyball. Int J Sports Med 1997;18:217. [8] Reeser JC, Verhagen E, Briner WW, Askeland TI, Bahr R. Strategies for the prevention of volleyball related injuries. Br J Sports Med 2006;40:594. [9] Divert C, Mornieux G, Baur H, Mayer F, Belli A. Mechanical comparison of barefoot and shod running. Int J Sports Med 2005;26:593–8. [10] Squadrone R, Gallozzi C. Biomechanical and physiological comparison of barefoot and two shod conditions in experienced barefoot runners. J Sports Med Phys Fitness 2009;49:6–13. [11] Webster KE, Kinmont JC, Payne R, Feller JA. Biomechanical differences in landing with and without shoe wear after ACL reconstruction. Clin Biomech (Bristol, Avon) 2004;19:978–81. [12] Decker MJ, Torry MR, Wyland DJ, Sterett WI, Richard Steadman J. Gender differences in lower extremity kinematics, kinetics and energy absorption during landing. Clin Biomech (Bristol, Avon) 2003;18:662–9. [13] DeVita P, Skelly WA. Effect of landing stiffness on joint kinetics and energetics in the lower extremity. Med Sci Sports Exerc 1992;24:108–15. [14] Zhang SN, Bates BT, Dufek JS. Contributions of lower extremity joints to energy dissipation during landings. Med Sci Sports Exerc 2000;32:812–9. [15] McNitt-Gray JL. Kinetics of the lower extremities during drop landings from three heights. J Biomech 1993;26:1037–46. [16] Burnfield JM, Powers CM. The role of center of mass kinematics in predicting peak utilized coefficient of friction during walking. J Forensic Sci 2007;52:1328–33. [17] Winter DA. Biomechanics and motor control of human movement. second ed. New York: Wiley; 1990. [18] Yeow CH, Lee PV, Goh JC. Sagittal knee joint kinematics and energetics in response to different landing heights and techniques. Knee 2010;17:127–31. [19] Hashemi J, Breighner R, Jang TH, Chandrashekar N, Ekwaro-Osire S, Slauterbeck JR. Increasing pre-activation of the quadriceps muscle protects the ACL during the landing phase of a jump: an in vitro simulation. Knee 2010;17:235–41. [20] Podraza JT, White SC. Effect of knee flexion angle on ground reaction forces, knee moments and muscle co-contraction during an impact-like deceleration landing: implications for the non-contact mechanism of ACL injury. Knee 2010;17:291–5. [21] Lim BO, Lee YS, Kim JG, An KO, Yoo J, Kwon Y. Effects of sports injury prevention training on the biomechanical risk factors of ACL injury in high school female basketball players. Am J Sports Med 2009;37:1728–34. [22] Yu B, Lin CF, Garrett WE. Lower extremity biomechanics during the landing of a stop-jump task. Clin Biomech (Bristol, Avon) 2006;21:297–305. [23] Yeow CH, Lee PVS, Goh JCH. Regression relationships of landing height with ground reaction forces, knee flexion angles, angular velocities and joint powers during double-leg landing. Knee 2009;16:381–6. [24] Nagano Y, Ida H, Akai M, Fukubayashi T. Gender differences in knee kinematics and muscle activity during single limb drop landing. Knee 2007;14:218–23. [25] Urabe Y, Kobayashi R, Sumida S, Tanaka K, Yoshida N, Nishiwaki GA, et al. Electromyographic analysis of the knee during jump landing in male and female athletes. Knee 2005;12:129–34. [26] Butler RJ, Crowell III HP, Davis IM. Lower extremity stiffness: implications for performance and injury. Clin Biomech (Bristol, Avon) 2003;18:511–7. [27] Pollard CD, Sigward SM, Powers CM. Limited hip and knee flexion during landing is associated with increased frontal plane knee motion and moments. Clin Biomech (Bristol, Avon) 2010;25:142–6. [28] Prilutsky BI. Eccentric muscle action in sport and exercise. In: Zatsiorsky V, editor. Biomechanics in sport: performance enhancement and injury prevention. Oxford: Blackwell Publishing; 2005. p. 56–86. [29] Williams III DS, Davis IM, Scholz JP, Hamill J, Buchanan TS. High-arched runners exhibit increased leg stiffness compared to low-arched runners. Gait Posture 2004;19:263–9.