Abstract
Stable walking depends on the coordination of multiple biomechanical degrees of freedom to ensure the dynamic maintenance of whole-body equilibrium as well as continuous forward progression. We investigated adult age-related differences in whole-body coordination underlying stabilization of center of mass (CoM) position and step pattern during locomotion. Sixteen younger (20-30 years) and 16 healthy older men (65–80 years) walked on a motorized treadmill at 80%, 100% and 120% of their self-selected preferred speed. Preferred speeds did not differ between the age groups. Motor-equivalent stabilization of step parameters (step length and width) and CoM position relative to the support (back and front foot) was examined using a generalized covariation analysis. Across age groups, covariation indices were highest for CoM position relative to the front foot, the measure most directly related to body equilibrium. Compared to younger adults, older adults showed lower covariation indices with respect to step length, extending previous findings of age-related differences in motor-equivalent coordination. In contrast, no reliable age differences were found regarding stabilization of step width or any of the CoM parameters. The observed pattern of results may reflect robust prioritization of balance over step pattern regularity, which may be adaptive in the face of age-associated sensorimotor losses and decline of coordinative capacities.
Highlights
Stable walking depends on the coordination of multiple biomechanical degrees of freedom (DOF) to ensure the dynamic maintenance of whole-body equilibrium as well as continuous forward progression
In the fore-aft direction (X), main effects of Speed were found for step length [F(2,60) = 1063.4, p,0.001, g2 = 0.59], center of mass (CoM) relative to back foot [F(2,60) = 779.3, p,0.001, g2 = 0.56], and CoM relative to front foot [F(2,60) = 625.9, p,0.001, g2 = 0.37], with mean values increasing with walking speed
In the fore-aft direction (X), significant main effects of Speed were found for step length [F(2,60) = 12.0, p,0.001, g2 = 0.14], CoM relative to back foot [F(2,60) = 9.93, p,0.001, g2 = 0.13], and CoM relative to front foot [F(2,60) = 22.3, p,0.001, g2 = 0.17]
Summary
Stable walking depends on the coordination of multiple biomechanical degrees of freedom (DOF) to ensure the dynamic maintenance of whole-body equilibrium as well as continuous forward progression. The present study extends this analysis to normal aging by examining the extent to which differences between younger and older healthy men in motor-equivalent coordination [5,6,7] are present in walking, and whether the pattern of age-related differences reflects functional priorities among performance requirements (e.g., balance versus regularity of the step pattern). Both the CoM position and foot placement depend on the configuration of many biomechanical DOF (e.g., joint angles) across the body. Different analytical approaches have been proposed to this end, such as the uncontrolled manifold (UCM) analysis [8] or the covariation by randomization method [10]
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