Time to task failure influences the postural alteration more than the extent of muscles fatigued.

The aim of this study was to compare the effects of unilateral and bilateral muscle fatigue on monopedal postural control. Nineteen subjects completed bilateral fatiguing contractions and unilateral fatiguing contractions of the quadriceps femoris until the torque output for both exercises dropped below 30% of the measured peak torque (the time to task failure was measured) for three consecutive contractions (independently measured for each leg). Postural control was evaluated by using a force platform which recorded center of foot pressure (COP) and was measured before and after the completion of both fatiguing tasks. Spatio-temporal COP parameters were used to evaluate postural control. The unilateral contractions affected monopedal postural control more than the bilateral fatiguing contractions (p<0.05). Moreover, the time to task failure was significantly longer for the unilateral contractions than for the bilateral contractions (p<0.05). The greater alteration of postural control for the unilateral fatiguing contractions compared to the bilateral fatiguing contractions could be related to a longer time to task failure which could provoke greater disturbances of the postural system in terms of sensory input and motor output.