Fatigue effects on body balance.

Body sway variables (sway area and sway path) were recorded by a dynamometric platform in 13 young subjects, standing quiet with feet together, with eyes open (EO) and eyes closed (EC), prior to and following two types of physical exercise (treadmill walking and cycle ergometer pedalling). Each exercise was performed under both fatiguing (above anaerobic threshold) and non-fatiguing conditions. Following fatiguing treadmill exercise, we observed a significant increase in body sway with respect to pre-exercise values. The increase was present under both visual conditions, affected both sway area and sway path and lasted until about 15 min from the end of the exercise. The Romberg quotient (the ratio of EC/EO of sway area, or sway path) significantly increased after the fatiguing exercise with respect to the non-fatiguing exercise. The mean position of the centre of foot pressure (CFP) was unchanged after the exercise. Fatigue induced an increase in the median frequency of oscillation of the centre of foot pressure, independent of the amplitude of sway. Non-fatiguing treadmill exercise induced no significant changes in sway or in its frequency content. Following fatiguing cycle ergometer exercise, a negligible increase or a decrease (under eyes closed condition) in body sway were observed. Non-fatiguing cycling exercise induced no significant changes or a decrease in sway. Control experiments showed that simple repetition of successive stance trials (without intercalated exercise) was able by itself to induce a decrease in sway. By taking this effect into account, both types of cycling exercises revealed a mild capacity to increase sway. We concluded that body sway increased after strenuous physical exercise, but was little affected by exercise performed below the estimated anaerobic threshold. The effects of fatigue on sway were short-lasting and of moderate extent, and therefore were not liable to seriously threaten body equilibrium.