How Do the Mechanical Demands of Cycling Affect the Information Content of the EMG?

Purpose: The persistence of phase-related information in EMG signals can be quantified by its entropic half-life (EnHL). It has been proposed that the EnHL would increase with the demands of a movement task, and thus increase as the pedaling power increased during cycling. However, simulation work on the properties of EMG signals suggests that the EnHL depends on burst duration and duty cycle in the EMG that may not be related to task demands. This study aimed to distinguish between these alternate hypotheses.

Methods: The EnHL was characterized for 10 muscles from nine cyclists cycling at a range of powers (35 to 260 W) and cadences (60-140 rpm) for the raw EMG, phase-randomized surrogate EMG, EMG intensity, and the principal components describing the muscle coordination patterns.

Results: There was phase-related information in the raw EMG signals and EMG intensities that was related to the EMG burst duration, duty cycle pedaling cadence, and power. The EnHL for the EMG intensities of the individual muscles (excluding quadriceps) and for the coordination patterns decreased as cycling power and cadence increased.

Conclusions: The EnHL provide information on the structure of the motor control signals and their constituent motor unit action potentials, both within and between muscles, rather than on the mechanical demands of the cycling task per se.