Stimulated and voluntary fatiguing contractions of quadriceps femoris similarly disturb postural control in the bipedal stance.

The aim of this work was to compare the effects of fatigue of the quadriceps femoris after fatiguing voluntary contractions (VOL) and fatiguing neuromuscular electrical stimulation (ES) on bipedal postural control. Nineteen active male subjects (22.2 ± 1.7 years) completed these two fatiguing exercises. Isometric maximal voluntary contraction (MVC) and postural control were recorded using an ergometer and a force platform that registered the center of foot pressure (COP). We analyzed the COP surface, the mean COP velocity and the spectral power density given by the wavelet transform. Recordings were performed before (PRE condition) and after the completion of each fatiguing task (immediately POST condition, after a 5 min recovery POST 5 condition). In POST condition, the ES exercise affected MVC more than the VOL exercise. However, bipedal postural control was similarly deteriorated for both exercises. In POST 5 condition, for both fatiguing exercises, muscle strength and postural control did not recover their initial level. These results suggest that the postural control disturbance could not be distinguished for the two fatiguing exercises in the bipedal stance. In addition, the recovery speeds of postural control and muscle strength abilities did not differ for the ES exercise and the VOL exercise.