The effects of walking step rate on ground reaction forces and muscle activation
Date
2013
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Publisher
University of Delaware
Abstract
It is well known that metabolic cost is minimized when walking at a preferred step rate. However, the relationship between step rate and other variables such as ground reaction forces and muscle activity is not well established. If altered step rates lead to increased forces, it could help to explain why certain populations (such as unilateral lower-extremity amputee subjects) experience increased joint loading on the intact limb. Higher joint forces are especially harmful to amputee subjects, who often develop knee osteoarthritis in their intact limb. The purpose of this study was to examine ground reaction forces and muscle activity associated with walking at step rates above and below preferred. In Part 1 of the study, 20 subjects walked under 7 step rate conditions at a constant speed of 1.3 m/s. The step rate conditions were preferred and -30%, -20%, -10%, +10%, +20%, and +30% steps/min from the preferred. In Part 2, subjects walked at the same step rates from Part 1, but step length was held constant by adjusting the treadmill speed for each condition. Motion capture, ground reaction forces, and EMG on 5 muscle groups (tibialis anterior, vastus lateralis, biceps femoris, medial head of gastrocnemius, and soleus) were recorded. A series of one-way repeated measures ANOVAs found significant (p<0.05) differences in all variables for both Parts. A U-shaped curve with the minimum at the preferred condition was found for the vertical ground reaction force, loading rate, and EMG data in Part 1. In Part 2, the same variables increased linearly with increasing step rate. These results show that at higher step rates (both with constant walking speed and constant step length) the ground reaction forces and muscle activity increase. Clinically, this is important because of the implications toward increased limb loading seen in amputee subjects and may help to explain why there is a higher rate of knee osteoarthritis in their intact limb.