Abstract
The purpose of this study was to investigate age-related differences in contractile and elastic properties of both dorsi- (DF) and plantarflexor (PF) muscles controlling the ankle joint in young and older adults. Experimental data were collected while twelve young and twelve older male and female participants performed maximal effort isometric and isovelocity contractions on a dynamometer. Equations were fit to the data to give torque-angle (Tθ) and torque-angular velocity (Tω) relations. Muscle series-elasticity was measured during ramped dynamometer contractions using ultrasonography to measure aponeurosis extension as a function of torque; second order polynomials were used to characterize the torque-extension (TΔL) relation. The results showed no age differences in DF maximal torque and none for female PF; however, older males had smaller maximal PF torques compared to young males. In both muscle groups and genders, older adults had decreased concentric force capabilities. Both DF and PF TΔL relations were more nonlinear in the older adults. Older PF, but not DF muscles, were stiffer compared to young. A simple antagonism model suggested age-related differences in Tθ and Tω relations would be magnified if antagonistic torque contributions were included. This assessment of static, dynamic, and elastic joint properties affords a comprehensive view of age-related modifications in muscle function. Although many clinical studies use maximal isometric strength as a marker of functional ability, the results demonstrate that there are also significant age-related modifications in ankle muscle dynamic and elastic properties.
Highlights
The functional capabilities of the dorsi- (DF) and plantarflexor (PF) muscles controlling the ankle joint are important in many activities of daily living
Ankle torque production depends on the joint position or angle, the joint angular velocity, and the series elasticity of the muscles crossing the joint
These peak torque data points may occur at different joint angles, appropriate adjustments should be made to account for the shape of the underlying Th relation [10]
Summary
The functional capabilities of the dorsi- (DF) and plantarflexor (PF) muscles controlling the ankle joint are important in many activities of daily living. Ankle torque production depends on the joint position or angle (the torque-angle relation; Th), the joint angular velocity (the torque-angular velocity relation; Tv), and the series elasticity (the torque-extension relation; TDL) of the muscles crossing the joint Together, these three relations reflect the active contractile and elastic properties of the muscles controlling the ankle joint. Many studies select the peak torque values generated at a range of joint angular velocities, and scale the data to the maximal value of the isometric Th curve [5,9]. These peak torque data points may occur at different joint angles, appropriate adjustments should be made to account for the shape of the underlying Th relation [10]
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