Effect Of Segmental Growth On The Force Construction Of Pedaling As A Function Of Speed

Abstract

Motor skill acquisition is characterized by improvements in the application of taskappropriate forces. Muscular and non-muscular forces act in concert to produce a resultant force that complies with the goal of the task. Non-muscular forces are directly dependent on the anthropometry of the performer. If the resultant force to be produced is the same between performers, inter-participant differences in anthropometry might require muscular adjustments to changing non-muscular forces. This effect might depend on movement speed as it also influences non-muscular forces. Differences in the application of muscular forces may therefore represent functional adjustments needed to account for changes in anthropometry. Such adjustments could pose confounds if age-related differences in muscular forces are to be attributed to features of the neuro-motor system. PURPOSE The purposes of this study were to determine (a) the effect of age-related changes in anthropometry on the application of muscular forces and (b) how this effect depends on movement speed. METHODS A torque-driven biomechanical model of two-legged pedaling was developed. The model tracked experimental kinematics and forces obtained from an experienced adult cyclist who signed informed consent before participating. The anthropometrics of the model were modified according to Jensen (1989). Segmental mass proportions, center of mass locations, and radii of gyration were scaled to children's dimensions (5, 7.5, and 10 years of age). Pedaling at 60 rpm and 120 rpm at a moderate resistance was simulated. The forces to be produced were scaled in proportion to body mass, and the kinematics were held constant across all simulations. This procedure enabled us to isolate the effect of differences in anthropometry on muscular force application. The muscular contribution to crank power was compared across age groups using ANOVAs (alpha=.05) and effect sizes (ES). RESULTS Relative changes in anthropometry between 5 and 10 years of age did not significantly influence muscular power production neither at 60 rpm nor at 120 rpm (p>.05). In addition, the effect sizes quantifying differences between age groups were small (mean ES=0.16). CONCLUSIONS The results demonstrate that during pedaling at a moderate resistance, changing anthropometry during childhood does not influence the force construction in pedaling over a broad range of movement speeds. It can therefore be concluded that during pedaling at these cadences, age-related differences in muscular force application can be attributed to features of the neuro-motor system. Supported by the National Science Foundation under Grant 9986221