Effects of utmost fatigue on undisturbed upright stance control

Abstract

Aim. – To assess the effects of utmost fatigue on balance control in upright quiet stance. Method. – Eleven subjects performed a postural task before and after completing a long distance triathlon. The centre of pressure (CP) displacements was recorded through a force platform and decomposed from a biomechanical relationship into two elementary motions: the horizontal motions of the centre of gravity (CG), and the difference CP – CG. These motions were then studied through three different analysis processes. Results. – A large increase of the oscillations is seen for both elementary motions. Interestingly, CG motions are particularly sensitive to fatigue and present an 83% increase for mean amplitudes while only a 44% increase is seen for CP – CG motions. Moreover, a large increase is observed in the mean time interval and the mean distance covered before a corrective process occurs. Finally, impairment of the muscular means brought into play and the decrease in ability to minimise body sways following utmost fatigue are discussed. Conclusion. – Postural instability following exhausting exercise is due both to muscular activity perturbation and to an impairment of the system’s capacity to control the position of the CG. This last point seems of a particular interest since it highlights a possible limit of the system to handle the controlled.