Quantification of human dynamic muscle fatigue by electromyography and kinematic profiles.

We wished to quantify the dynamic muscle fatigue by electromyographic (EMG) and kinematic parameters during uphill walking (5 km/h, 25%). The muscle coordination between biceps femoris, semitendinosus, vastus lateralis, gastrocnemius medialis, soleus, and tibialis anterior was evaluated by measuring (a) the period from onset of the EMG burst to heel contact, and (b) duration of the EMG burst. The muscle activity of the individual bursts was evaluated by the root mean-square (RMS), the mean power frequency (MPF), and the averaged EMG profile during one stride cycle. The most pronounced differences at the start and end of the endurance test were observed in the semitendinosus and the biceps femoris. The gastrocnemius was recruited substantially closer to heel contact, but no changes were noted in the soleus. The RMS and duration of the EMG burst were changed significantly for the vastus lateralis. The overall pattern of the kinematic profiles (position, and velocity) for the upper and lower leg remained constant, although the muscle activity and coordination changed. During dynamic muscle fatigue, a complex interaction between muscle coordination and muscle performance was noted, but how the central nervous system control this interaction is not known.