Task Dependent Synchronization of Motor Units of the Medial Gastrocnemius Muscle Revealed in EMG-Currents

Human movements have to be very tightly controlled by the neuro-muscular control mechanisms. In free style ski jumps the muscular events were as short as or shorter than 50ms and inter muscular co-contractions started and were synchronized within a time range of less than 5ms [1]. The Piper rhythm shows a neuromuscular control mechanism that can be seen in the EMG during isometric contractions as well as during movements [24]. It was reported that the power of the EMG signal of runners varied with the Piper Rhythm and in turn the Piper rhythm varied with running speed [5]. For the neuromuscular control to generate a Piper rhythm in the frequency range of 20Hz to 50Hz means that motor units (MUs) must be accurately timed and thus synchronized within a time frame of less than 50ms which corresponds to higher rates of MU firing [6]. The coordinated muscle activation significantly changes in patients suffering from osteoarthritis, however, up to now, the result of this synchronization was revealed in the fluctuations of EMG-power but has not been observed in the raw EMG signal [7].