Unilateral and bilateral fatiguing contractions similarly alter postural stability but differently modify postural...

The aim of the present study was to compare the effects of unilateral and bilateral muscle fatigue on bipedal postural control and neuromuscular activities. Nineteen subjects completed bilateral fatiguing contractions (BI group), and seventeen subjects completed unilateral fatiguing contractions (UNI group) of the quadriceps femoris. Postural control, maximal voluntary contraction (MVC) and central activation ratio (CAR) were measured before and after the completion of fatiguing tasks for both groups. Postural control was evaluated by using a force platform, which recorded the center of foot pressure (COP). MVC was quantified with an ergometer and CAR was determined with the superimposed electrical stimulation technique. Spatio-temporal COP parameters were used to evaluate postural stability (displacements of COP) and postural position (coordinates of COP) and a frequency analysis of COP excursions (wavelet transform) was performed to estimate the contribution of different neuronal loops. Postural stability, MVC and CAR were similarly affected after unilateral and bilateral fatiguing contractions. Moreover, the impairment of postural position was higher after unilateral fatiguing contractions than after bilateral fatiguing contractions. The study's results indicated that unilateral and bilateral fatigue equally disturbs postural control as well as central drive. However, unilateral muscle fatigue creates postural asymmetries while bilateral muscle fatigue does not engender any.