Lower body muscle activity profile when running under various conditions

The objectives were to compare: 1) the level of activation for selected thigh and shank muscles when participants (n=13) ran overground versus on a treadmill at three grades; 2) the EMG profile of ankle stabilizer muscles and stride-time variability when individuals (n=27) with or without CAI ran on a treadmill. METHODS: EMG activity of selected thigh and shank muscles as well as tibial acceleration data were recorded during the running trials. EMG amplitude, timing of EMG peaks, and variation in stride-time were analyzed from 50 consecutive stride cycles. EMG data were time normalized to stride duration and amplitude-normalized to the appropriate maximal voluntary contraction (MVC) task. RESULTS: EMG amplitude during overground running matched the values measured when running on a treadmill at 1% grade for thigh muscles and at 2% grade for shank muscles. Also, stride time was more variable during overground running and was associated with elevated EMG amplitudes for some leg muscles. Individuals with CAI had similar EMG amplitudes and peak timing, but an altered order of peak EMG activity in ankle stabilizer muscles, and a greater stride-time variability during treadmill running compared with individuals who had no history of ankle sprains. CONCLUSION: These findings 1) suggest caution when extrapolating findings obtained from running on a treadmill at 0% grade to the overground performance capabilities of healthy young adults; 2) indicate that individuals with CAI exhibit altered activation strategies for ankle stabilizer muscles when running on a treadmill.