Kinematics and Kinetics of Drop Jump Landings: Shod and Barefoot

Kinematics and Kinetics of Drop Jump Landings: Shod and Barefoot Conducted at the University of Arkansas, Fayetteville, Arkansas Gretchen D. Oliver, PhD, FACSM, ATC, LAT Assistant Professor School of Kinesiology Auburn University Ryne Eubanks Graduate Athletic Training Student Department of Health Science, Kinesiology, Recreation, and Dance University of Arkansas ABSTRACT The purpose of this study was to examine drop jump landings while shod and barefoot. It was hypothesized that barefoot would result in more efficient landing mechanics. Sixteen National Collegiate Athletic Association soccer players [19.2 + 1.0 yrs; 68.9 + 8.7 kg; 168.6 + 6.6 cm] who were listed on the active playing roster and deemed free of injury participated. Participants were instructed to drop down from a 47 cm box and then perform a vertical jump for barefoot and shod conditions. Paired samples t-test revealed significant differences between barefoot and shod conditions. At maximum ground reaction force there was greater knee moment while shod [t=2.41, p=0.04], and at maximum knee flexion, the barefoot condition revealed lower hip and knee moments [t=3.91, p=0.00; t=2.56, p=0.03 respectively]. It was concluded that by training in an unshod condition might enable the limb to develop a more appropriate neuromuscular landing pattern. INTRODUCTION With the majority of ACL injury in females being noncontact, focus has been on neuromuscular training particularly in jump landings. Neuromuscular training programs have provided positive benefits of injury prevention in high risk female athletes (Hewett, Lindenfield, Riccobene, & Noyes, 1999; Hewett, et al., 2005; Myer, Ford, Palumbo, & Hewett, 2005; Myer, Brent, & Hewett, 2005). Neuromuscular training has focused on the biomechanics that are associated with high knee abduction moments (Ireland, 2002; Zazulak, Hewett, Reeves, Goldberg, & Cholewicki, 2007) as well as trunk and hip control (Myer, Brent, Ford, & Hewett, 2008; Myer, Chu, Brent, & Hewett, 2008), and front plane knee control (Myer, Ford, Brent, Hewett, 2007; Myer, Ford, Khoury, Succop, & Hewett, 2011) during jump landings. In addition the neuromuscular training also focuses on the sensorimotor system of incorporating proprioception into the landing strategies. There might be some ease in implementing neuromuscular training programs on the collegiate or professional levels of competition, but Volume 1 Number 2 September 2013 Journal of Athletic Medicine Page 85

those settings who do not employ properly trained clinicians such as the high school might have some difficulty in administering these protocols (Myer et al., 2005). Also, performing these programs with a large team might deter some coaches, as it becomes a time-consuming task (Myer et al., 2005). Providing correct biomechanical instruction and implementing neuromuscular landing strategies at the earliest age possible could be most effective technique to proper landing biomechanics (Myer et al., 2011). As barefoot running has become popular, it has been documented that running barefoot allows for more sensory input upon landing, thus allowing the individual to adjust leg stiffness (Jenkins, & Carthon, 2010). In addition, it has been proposed that those who train barefoot are able to avoid high impacts by their ability to sense high rates of loading when they occur and thus adjust their mechanics appropriately (Marti, Vander, Minder, & Abelin, 1988). There is a general thought that those who train barefoot could be susceptible to increased injury rates (Lieberman, 2012). An evolutional concept holds that shod running might inhibit proprioceptive response (Lieberman, 2012). It has been hypothesized that running barefoot, especially in childhood, would encourage the natural formation of the foot within the proprioceptive response (Lieberman, 2012). The modern-day shoe complete with soles, arch supports, and features that control biomechanical deviations could prevent the body from adapting to stresses which were once normal before the latest technological advances (Lieberman, 2012). Thus with neuromuscular training injury reduction programs it is questioned if some of the training should be performed barefoot. Therefore it was the purpose of this study to compare knee and hip kinematics and kinetics in drop jump landings while shod and barefoot. It was our hypothesis that barefoot landings would result in significantly different kinematics and kinetics during drop jump landings. METHODS A controlled laboratory study design was implemented. Sixteen Division I National Collegiate Athletic Association soccer players [19.2 + 1.0 yrs; 68.9 + 8.7 kg; 168.6 + 6.6 cm] who were listed on the active playing roster and deemed free of injury volunteered to participate. Participants were excluded if they had suffered an injury within the past 6 months. The University Institutional Review Board approved all testing protocols. Approved testing procedures were explained to each participant and informed consent and participant assent were obtained before testing began. Participants had a series of eight electromagnetic sensors (Flock of Birds Ascension Technologies Inc., Burlington, VT) attached at the following locations: (1) the medial aspect of the torso at C7; (2) medial aspect of the pelvis at S1; (3-4) bilateral distal/posterior aspect of the upper leg; (5-6) bilateral distal/posterior aspect of the lower leg; and (7-8) bilateral proximal dorsum of the foot (Myers, Laudner, Pasquale, Bradley, & Lephart, 2005; Oliver, & Plummer, 2011). Sensors were affixed to the skin using double-sided tape and then wrapped using flexible hypoallergenic athletic tape to reduce movement artefact. In addition, sensors were placed over areas with the least muscle mass in an attempt to minimize sensor movement. Following sensor placement, a 9 th sensor was attached to a wooden stylus and used to digitize the palpated positions of the body landmarks (Myers et al., 2005; Oliver et al., 2011; Wu et al., 2002). Participants were instructed to stand in anatomical neutral while selected body landmarks were accurately digitized. The coordinate systems used were in accordance with the International Society of Biomechanics Recommendations (Wu et al. 2002). Data describing the position and orientation of electromagnetic sensors were collected at 100 Hz. Raw data were independently filtered along each global axis Volume 1 Number 2 September 2013 Journal of Athletic Medicine Page 86

using a 4 th order Butterworth filter with a cutoff frequency of 13.4 Hz [Oliver, & Keeley, 2010a, Oliver, & Keeley 2010b]. Two points described the longitudinal axis of the segment and the third point defined the plane of the segment. A second axis was defined perpendicular to the plane and the third axis was defined as perpendicular to the first and second axes. Neutral stance was the y- axis in the vertical direction, horizontal and to the right of y was the x-axis, and posterior was the z- axis (Oliver et al., 2011). After all sensors were secured the participants were given a randomized order of foot condition: shod and barefoot. Participants were instructed to drop down from a 47 cm box and then perform a vertical jump. Each participant was instructed to land on a 40 x 60 cm Bertec force plate (Bertec Corp, Columbus, Ohio) that was anchored into the floor. Each participant performed five drop jumps for each of the two foot conditions [shod and barefoot]. The shod condition allowed each participant to wear her team issued training shoe. Data from the third drop landing of each condition were selected for analysis. The third trial was selected to assure that the participant was accustomed to the protocol and the foot condition. Data Analysis Landings were divided into two phases: [1] initial drop landing and [2] vertical jump landing. We examined the second phase of the drop jump, the vertical jump landing, in attempt to best simulate an athletic movement. Within the two phases, landings were divided into two events of [1] maximum vertical ground reaction force, and [2] maximum amount of knee flexion achieved. Statistical analyses were performed using IBM SPSS (IBM, Armonk, New York). Data were analyzed with a level of significance set at p 0.05 to determine if foot condition [barefoot, shod] allowed for differences in landing mechanics. RESULTS Paired samples t-test revealed significant differences between barefoot and shod conditions at both instances of maximum ground reaction force and knee flexion. At maximum ground reaction force there was a significantly greater knee abduction moment while shod [t=2.41, p=0.04]. While at the instant of maximum knee flexion, the barefoot condition revealed significantly lower hip and knee moments [t=3.91, p=0.00; t=2.56, p=0.03 respectively]. Means and standard deviations of all variables are presented in Table 1. Volume 1 Number 2 September 2013 Journal of Athletic Medicine Page 87

Table 1. Means and standard deviations of kinematic and kinetic variables. Shod GroundRX N Flexion Barefoot GroundRX N Flexion Hip Flexion[ ] 42.5+13. 0 72.1+27. 9 38.9+13. 4 65.5+23. 2 Valgus[ ] abduction moment [-]= valgus; [+]=versus Flexion[ ] 5.5+5.4 47.1+11. 9 9.6+6.9 74.5+20. 9 5.9+7.9 48.5 + 8.8 8.7+8.7 71.3+15. 5 Hip Moment[N] Moment[N] Ground RXN [N] 364.1+370.9-25.3+158.3 1378.9+641.4 76.6 + 127.1-7.5 + 26.6 837.9 + 436.8 897.8+985.4 37.3 + 33.3 1832.8+418.9 178.0+129.8 32.7+50.6 1066.5+208.2 DISCUSSION Increased knee moments, particularly abduction, during landing are known to predict ACL injury in females (Myer et al., 2011; Krosshaug et al., 2007; Olsen, Myklebust, Engebretsen, & Bahr, 2004). In addition landing with reduced knee flexion contributes to greater knee abduction moments (Myer et al., 2011). The current study revealed that landing barefoot allowed for greater knee flexion as well as decreased knee and him moments. The results of this study are significant in that the barefoot jump landings demonstrated overall lower knee and hip moments. This difference can be explained due to the shock absorbing capacity of the shoes serving to delay the timing the lower extremity feels the ground reaction force and the kinetic energy from the landing being distributed into a limb not prepared for the energy transferred distally. As the limb attempts to catch up to the energy the hip and knee move through a greater arc and subsequently take longer to dissipate the force from the landing. In the barefoot condition, ground reaction is immediately taken up into the limb and the musculature reaction time is decreased due to the quicker and lager load allowing for efficient energy dissipation though the limb thereby limiting the hip and knee movements, as the limb does not have any masking or absorption of the ground reaction force to counteract the kinetic energy transferred from the jump landing. In addition the improved landing strategy may be pavlovian in that barefoot landing conditions will encourage the jumper to more adequately and quickly dissipate the force in the musculature due to the pain from landing hard. Females tend to be deficient in neuromuscular control of their lumbopelvic-hip complex. This neuromuscular deficit results in increased lower extremity joint loads sustained during sporting activities (Myer et al., 2011). Our results revealed that landing from a jump barefoot we Volume 1 Number 2 September 2013 Journal of Athletic Medicine Page 88

were able to decrease those lower extremity joint loads. Thus postulating that training barefoot could enhance neuromuscular training of efficient landing mechanics. Further research is warranted to examine the effects neuromuscular training while barefoot in attempt to increase neuromuscular control and decrease joint loads during sporting activities. REFERENCES Boden, B.P., Dean, G.S., Feagin, J.A., and Garrett, W.E. (2000). Mechanisms of anterior cruciate ligament injury. Orthopedics, 23, 573-578. Hewett, T.E., Lindenfeld, T.N., Riccobene, J.V., and Noyes, F.R. (1999). The effect of neuromuscular training on the incidence of knee injury in female athletes: A prospective study. American Journal of Sports Medicine, 27, 699-706. Hewett, T.E., Myer, G.D., Ford, K.R., Heidt, R.S., Colosimo, A.J., McLean, S.G., van der Bogert, A.J., Paterno, M.V., and Succop, P. (2005). Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: A prospective study. American Journal of Sports Medicine, 33, 492-501. Jenkins, D.W., and Carthon, D.J. (2010). Barefoot running claims and controversies: A review of the literature. Journal of the American Podiatric Medical Association, 101, 231-246. Krosshaug, T., Nakame, A., Boden, B.P., Engebretsen, L., Smith, G., Slauterbeck, J.R., Hewett, T., and Bahr, R. (2007). Mechanisms of anterior cruciate ligament injury in basketball: video analysis of 39 cases. American Journal of Sports Medicine, 35, 359-367. Lieberman, D.E. (2012). What we can learn about running from barefoot running: an evolutionary medical perspective. Exercise and Sport Science Reviews, 40, 63-72. Myer, G.D., Ford, K.R., Palumbo, J.P., and Hewett, T.E. (2005). Neuromuscular training improves performance and lower extremity biomechanics in female athletes. Journal of Strength and Conditioning Research, 19, 51-60. Myer, G.D., Ford, K.R., Brent, J.L., and Hewett, T.E. (2005). The effects of plyometric versus dynamic balance training on landing force and center of pressure stabilization in female athletes. British Journal of Sports Medicine, 39, 397. Ireland, M.L. (2002). The female ACL: Why is it more prone to injury? Orthopedic Clinics of North America, 33, 637-651. Myer, G.D., Brent, J.L., Ford, K.R., and Hewett, T.E. (2008). A pilot study to determine the effect of trunk and hip focused neuromuscular training on hip and knee isokinetic strength. British Journal of Sports Medicine, 42, 614-619. Volume 1 Number 2 September 2013 Journal of Athletic Medicine Page 89

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Zazulak, B.T., Hewett, T.E., Reeves, N.D., Goldberg, B., and Cholewicki, J. (2007). The effects of core proprioception on knee injury: A prospective biomechanical epidemiological study. American Journal of Sports Medicine, 35, 368-373. Table Legend: Table 1: Means and standard deviations of kinematic and kinetic variables at the instance of maximum ground reaction force and knee flexion. Volume 1 Number 2 September 2013 Journal of Athletic Medicine Page 91