Single-Joint Jump Height Correlates with Heel Length and Toe Length, H Van Werkhoven, SJ Piazza

Tags: toe length, jump height, Herman van Werkhoven, correlations, optimal performance, foot length, maximal height, Stephen J. Piazza, distance running, motor tasks, heel and toe, The Pennsylvania State University, moment arms
Content: SINGLE-JOINT JUMP HEIGHT CORRELATES WITH HEEL LENGTH AND TOE LENGTH Herman van Werkhoven, Stephen J. Piazza The Pennsylvania State University, University Park, PA, USA email: [email protected]
INTRODUCTION Several recent studies have identified associations between foot and ankle structure and locomotor function. For example, the length of the heel has been found to correlate positively with energetic cost during running [1,2] and toe length has been found to correlate with toe flexor work during running [3]. Other studies have demonstrated that human sprinters have smaller Achilles tendon moment arms and longer toes than height-matched non-sprinters [4,5]. It is not clear, however, whether similar correlations between foot structure and performance exist for maximal height jumping. Individuals with longer heels might be expected to have longer plantarflexor moment arms and thus better leverage for raising the body's center of mass. Musculoskeletal computer simulations have suggested, however, that large moment arms might reduce plantarflexor force due to force-velocity effects [4,6] and thus reduce moment and power during rapid plantarflexions. The aim of this study was to test for correlations between performance in a single-joint maximalheight jumping task and either heel length or toe length. A single-joint jumping task was considered in order to allow for a focused investigation into the mechanisms of Optimal Performance. We hypothesized that jump height would correlate negatively with heel length, as each jump involves a rapid plantarflexion and shortening of the muscle fibers, but that jump height would correlate positively with toe length because longer toes would facilitate toe flexor work on the center on mass. METHODS Eight healthy male subjects performed five maximal height static jumps (without countermovement) `
using only the ankles (and not the knees or hips) for propulsion. Each subject wore braces to immobilize the knee joint and each was instructed not to rotate at the hips, bend the trunk, or move the arms or head. The arms were held stationary across the chest. Subjects wore platform shoes (JumpSoles, Metapro; Mountain View, CA) and a block was placed below the heel to prevent a countermovement. Kinematics of the foot and shank were collected in order to calculate ankle angles. The peak rise of the centroid of four markers situated on the sacrum were used to measure jump height. Several foot, ankle and lower leg anthropometric values were recorded for each subject. These included: height; mass; lower leg length; maximum lower leg circumference; foot length; heel length (horizontal distance from lateral malleolus to back of the heel); and first toe length (distance from first metatarsal head to distal end of the hallux). Correlation analyses were performed between all anthropometric variables and the jump height for each subject was averaged over five trials. RESULTS AND DISCUSSION Strong significant correlations were found between jump height and both heel length and toe length (Table 1, Figure 1, and Figure 2). No significant correlations were found between jump height and any of the other anthropometric variables. Contrary to our hypothesis, a positive rather than a negative correlation was found between jump height and heel length (Figure 1). Our finding indicates that subjects with larger plantarflexor moment arms jump higher, suggesting that the increased leverage that follows from a longer plantarflexor moment arm outweighs the potential force reductions due to force-velocity effects. Previous studies have shown
Table 1: Correlations between anthropometric variables and average jump height (N=8, * p0.05)
body mass
lower leg length
lower leg circumference
foot length
toe length
0.75 0.006*
heel length
0.71 0.009*
sprinters to possess smaller than normal plantarflexor moment arms, but it is possible that trained sprinters have undergone adaptations not found in our untrained subjects. Previous modeling studies have suggested that a longer toe extends the duration of contact with the ground for sprinters, increasing the potential for forward propulsion [4,5]. This same mechanism could enhance maximal height jumping performance as a longer toe may keep the foot in contact with the ground longer and thus permit the muscles with more of an opportunity to propel the center of mass upwards. The correlations we found are not simply a reflection of taller or heavier subjects jumping higher. Neither height nor body mass was correlated with jump height. A moderate correlation trending towards significance (R2 = 0.41, p = 0.085) was found between foot length and jump height, although this dependency was not as strong as THE RELATIONSHIPs between heel length and jump height or toe length and jump height. Interestingly, foot length was strongly correlated with heel length (R2 = 0.74, p = 0.006), but was not significantly correlated with toe length (R2 = 0.16, p = 0.328). We are currently working to develop a modified version of an existing computational simulation of the single-joint jumping task [7] to help explain the experimental findings of this study. CONCLUSIONS maximal performance in a single-joint ankle
jumping task was found to be significantly correlated with heel length and with toe length. For other motor tasks (e.g., sprinting and distance running) different combinations of heel and toe proportions seem to be favorable. Further investigation is needed to understand the mechanisms by which foot morphology potentially influences performance in different tasks and how differences in foot structure arise. Figure 1: Correlation between average jump height and heel length (R2 = 0.71, p = 0.009). Figure 2: Correlation between average jump height and toe length (R2 = 0.75, p = 0.006). REFERENCES 1. Scholz MN, et al. J Exp Biol 211, 3266-3271, 2008. 2. Raichlen DA, et al. J Hum Evol 60, 299-308, 2011. 3. Rolian C, et al. J Exp Biol 212, 713-721, 2009. 4. Baxter JR, et al. P R Soc B 279, 2018-2024, 2012. 5. Lee SSM, et al. J Exp Biol 212, 3700-3707, 2009. 6. Nagano A, et al. J Biomech 36, 1675-1681, 2003. 7. van Werkhoven H, et al. J Biomech, in press.

H Van Werkhoven, SJ Piazza

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