Motor control

Document Type



The purpose of this study was to measure the pedal force magnitude and direction in the power phase of cycling for increasing force application in unconstrained (force direction was not constrained) and for constrained (force direction had to be perpendicular to the crank) conditions. Participants exerted forces on the pedal while the resultant force magnitude and direction, and the associated electromyographic activity of major lower limb muscles, were measured. Force direction for the constrained situation was maintained with a single muscle synergy across all levels of effort, suggesting that force direction is a strong regulator of muscle synergies. In contrast, for the unconstrained condition, muscle synergies switched to an ankle extensor strategy with muscular effort, and force direction typically changed significantly, suggesting that increasing muscle effort is associated with variable muscle synergies. We speculate that with increasing muscle effort, the preferred muscle synergies take advantage of the functional capabilities of the synergistic muscles.