Control of Walking Speed in Young and Old Adults

Walking is a basic form of locomotion and walking velocity is a good predictor of human health with faster velocities indicating better health. While faster walking velocities have been attributed to overall increases in lower extremity joint torques and powers the precise relationships of torque and power outputs at each joint to walking velocity remain elusive. We proposed that these relationships are fundamental in developing effective training programs aimed at increasing walking velocity in mobility-challenged populations such as older adults. Based on the previously established argument that aging induces asymmetric changes in joint torques and powers we hypothesized that walking velocity is more strongly related to hip torque and power than ankle torque and power in old adults than young adults. The purpose of this study was to identify the relationships among maximum sagittal plane hip knee and ankle joint torques and powers and walking velocity in young and old healthy adults in order to identify biomechanical correlates associated with modulating walking velocity. Gait biomechanics were collected using 8 camera 3D motion capture and force platform systems. Twenty-two young healthy adults and twenty-two old healthy adults each walked at 20 speeds ranging from relatively slow to relatively fast velocities. Maximum sagittal plane joint torques and powers derived through inverse dynamics were correlated to walking velocity (p<0.05). The data showed that all peak torques and powers were significantly (p<0.05) and directly related to walking velocity. Hip and ankle relations were curvilinear upward and downward; knee were linear. Peak joint torques showed proximal to distal decrease in the strength of their relationships. Peak joint powers were similarly related to walking velocity at each joint. In old adults torques were most strongly related to walking velocity at the proximal hip (R²=0.761) and decreased distally to the ankle (R²=0.275); powers were similar to walking velocity across the hip (R²=0.467) and the ankle (R²=0.445). In young adults torques were also most strongly related to the walking velocity at the proximal hip (R²=0.747) and decreased distally to the ankle (R²=0.289); powers were similarly related to walking velocity across the hip (R²=0.601) than to the ankle (R²= 0.528). Overall mechanical output at the hip was the primary biomechanical correlate of walking velocity whereas mechanical output at the ankle was most weakly correlated to walking velocity. This pattern of modulating walking velocity is used by both young and old adults similarly. Therefore the hypothesis was refuted as aging does not cause a mechanical plasticity in relation to walking velocity