A collision-based analysis of the landing-takeoff asymmetry during running
(2017) Computer Methods in Biomechanics and Biomedical Engineering — Vol. 20, n° sup1, p. 65-66 (2017)
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- Authors
Willems, Patrick 
- Abstract
- During running, a major source of energy loss is the redirection of the center of mass (COM) motion from downward to upward during stance. This down-to-up redirection could, as a first approximation, be considered as a collision with the ground (Ruina et al., 2005). A collision occurs when a perpendicular relationship between force and velocity vector is not maintained; the angle of deviation from this relationship is called by Ruina et al. (2005) the collision angle (ϕ). These authors showed that the energy losses could be minimized via suitable path matching of the leg as it collides with the ground. During the first part of the stance phase (absorptive part), ϕ is negative and energy is absorbed by extending muscles and tendons as well as by deformation of other tissues (Fig. 1A). During the second part (generative part), ϕ is positive and energy is generated by muscles and tendon recoil (Fig. 1B). When the collision angle of the absorptive deceleration phase mirrors the subsequent collision angle of the generative acceleration phase, the collision is kinematically equivalent to a ‘pseudo-elastic collision’, which minimizes the collisional energy losses, reducing the muscular work. Currently, collision-based analyses of human gait are done assuming that the COM within a step is symmetric around the mid-step (Lee et al., 2013). However, differences in mechanical events taking place during the descent and the lift of the center of mass occur during running (Cavagna, 2006). This deviation from a symmetrical pattern, defined by Cavagna as the ‘landing-takeoff asymmetry’, results from a distinctive response of the muscle-tendons units during the absorptive and generative phases because (i) according to the force-velocity relation, muscular force is greater during stretching than during shortening and (ii) a dissimilarity exists in the lever system (Cavagna et al., 2010). According to this author, the ‘landing-takeoff asymmetry, which would be nil in the elastic rebound of the symmetric spring-mass model for running, suggests a less efficient elastic energy storage and recovery during the bouncing step’. We hypothesize that, due to landing-takeoff asymmetry, the average collision angle is different during the absorptive and generative part of stance, reflecting a deviation from a pseudo-elastic behavior. Therefore, we have measured the collision parameters during running on the level at different speeds.
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Dewolf, A., & Willems, P. (2017). A collision-based analysis of the landing-takeoff asymmetry during running. Computer Methods in Biomechanics and Biomedical Engineering, 20(sup1), 65-66. https://doi.org/10.1080/10255842.2017.1382863 (Original work published 2017)