Speed and/or inclination-dependent mobilization of human leg muscles during walking with a unique exception

Treadmill walking exercise is not always effective for prevention of detrimental effects on soleus muscle caused by gravitational unloading. Thus, the effects of walking speed and/or uphill inclination on the mobilization of leg muscles were studied to reconsider the optimum prescription for the countermeasure. The subjects performed barefoot walking exercise on a treadmill at 4 and 6km/h and at a 0, 6, 10, and 15% uphill incline. The activity of electromyogram (EMG) was recorded in soleus, lateral portion of gastrocnemius, and tibialis anterior muscles. In addition, the total time spent for each step (step duration from landing to the next landing of the left foot) and the time soleus was active per step (EMG burst duration) during each step were determined. Furthermore, video was recorded to measure the ankle and knee joint angles in the front and back foot, when the front foot landed on the treadmill. Most of the subjects stepped down using the heel (rear-foot strike), but one subject stepped down using the fore-foot (fore-foot strike). The EMG activity of soleus in the rear-foot strikers was elevated with an increase in treadmill inclination and/or speed. In contrast, soleus EMG activity was decreased in the fore-foot striker under the same conditions, whereas the EMG activity of gastrocnemius was increased. These results indicate that individual differences in foot-strike patterns should be considered for the optimum prescription of walking as an exercise countermeasure and suggest that similar considerations may be warranted for other exercise countermeasures. •We analyzed the activation patterns of leg muscles during walking in human subjects.•Subjects were divided by foot-strike patterns into the rear- and fore-foot strikers.•In rear-foot strikers, soleus was activated when angle and speed were increased.•Soleus activity was decreased, when intensity was increased in a fore-foot striker.•Foot-strike patterns should be considered to obtain beneficial effect of walking.