Physical Activity, Exercise Physiology, Movement
The effect of walking speed on transient responses to visual perturbations
(School of Public Health (UMD) Kinesiology Doctoral Student)
Ehtemam, Farzad (Kinesiology), Kiemel, Tim (Kinesiology)
Previous research has shown that a change in speed is an indicator of health decline in neurological and geriatric populations. In order to understand the underlying mechanisms of speed control and their variations across different populations, it is necessary to understand how changes in muscle activities are affected by modulation of speed. It is not well understood how the transient changes in muscle activations are related to steady-state conditions. The purpose of this study was to compare and contrast the transient changes in muscle activations as a function of speed to steady-state conditions. Ten healthy adults walked on a treadmill in a virtual reality environment at three different speeds. The visual scene in front of the subjects was perturbed to create the perception of self-motion relative to the surrounding dark room. Electromyography was recorded from leg muscles to derive muscle activation profiles. Transient changes in muscle activations were described by phase-dependent impulse response functions, which were computed using harmonic transfer functions. The transient changes in activations are highly dependent on the phase of stimulus. However, at certain phases for each muscle, the transient and steady-state changes share some qualitative features. Both show increases in activities with an increase in speed that depends on the phase of the gait cycle. Changes in activations of plantarflexor muscles show an increase with speed around the push-off phase of the gait cycle while changes in dorsiflexor activations are increased closed to heel strike. We observed similarities between steady-state and transient changes in muscle activations as the speed of walking changes. One shared characteristic was the increase in the activity of tibialis anterior (TA). This increase in activation of TA with increase in speed suggests a role for TA in speed control. The observed result here shows that increased activity of TA in addition to plantarflexor activity at push off can contribute to control of speed. Another finding was a decrease in the transient activity with increase in speed prior to push-off for plantarflexors. This pattern of activity has not been observed before and might be unique to control of speed during transient responses.