Effects of repeated ankle plantar-flexions on body sway during standing

The study investigated relations between effects of repeated ankle plantar-flexion movements exercise on the soleus Hoffmann (H)reflex and on postural body sway when maintaining upright stance. Ten young volunteers performed five sets of ankle plantar-flexionsof both lower limbs. Assessment of the feet centre-of-pressure (COP) displacement and H-reflex tests were carried out in quiet stancebefore, during and after the exercise. H-max and M-max responses were obtained in 8 subjects and reported as the peak-to-peakamplitudes of the right soleus muscle electromyographic waves. Mean dispersion of COP along the antero-posterior direction increasedsignificantly during the exercise; whilst the overall H-reflex response indicated a reduction without a concomitant modification in theM-max response. H-reflex responses, however, varied between participants during the first sets of exercise, showing two main trendsof modulation: either depression or early facilitation followed by reduction of the H-reflex amplitude. The extent of reflex modulationin standing position was correlated to the concentric work performed during the exercise (r = 0.85; p < 0.01), but not to the anteroposteriorCOP dispersion. These results suggest that during a repeated ankle plantar-flexions exercise, modulation of the H-reflexmeasured in upright stance differs across individuals and is not related to changes of postural sway.