In this paper we present the observation where 10 healthy subjects of mean age 25 are examined to find out a relationship between postural sway during quite-stance and perturbation with and without muscle fatigue. We also observe the effect of vision on postural sway on both normal and fatigued conditions.
Human control of upright body posture involves inputs from several senses (visual, vestibular, proprioceptive, somatosensory) and their central interactions. Multiple sensory systems of human body are involved in tandem for controlling quite standing. Studies show that there is an indirect and presumably cognitive relationship between visual effects on posture control and their intersensory interactions (BLMLEA. et al, 2006).
During quite stance position, center of mass (COM) is stabilized over base of support by using low level muscular movements and body sways around the point of support like an inverted pendulum (Johansson R, Magnusson M, Akesson M. 1988). This led to the hypothesis of inverted pendulum. Any defect, alteration or malfunctioning of the sensory or motor components increases body sway and hence increases the muscle activity to maintain postural equilibrium (Dietz V. 1992). Minor perturbations occurring during normal stance can be counteracted by the regulation of ankle muscles (Schieppati M et al, 1994 and McClenaghan BA et al 1996).
Muscle fatigue is a complex phenomenon that has been defined as a reduction in the force-generating capacity of muscles, regardless of the task performed (Bigland-Ritchie B, Woods JJ.1984). Though, how fatigues affect the postural control system is not clear there are several fatigue related mechanisms involved at different levels of the nervous system that could affect the regulation of these small forces. Muscle fatigue causes failure of transmission of neural signals and disables the muscles to respond to the neural currents (Bigland-Ritchie B, Woods JJ.1984). Muscle fatigue also alters the basic functioning of complete nervous system and causes failure of motoneurons excitement.
Effects of a muscle fatigue on human postural sway can be studied by inducing momentary fatigue by physical exertion. Studies show a mild difference in effects of a fatigue on sway with and without vision (Lepers R. and Nardone A. et al).
To examine the effects of a fatigue on human postural control, in this experiment muscle fatigue is induced in ankle