MODELING EFFECTS OF MUSCLE FATIGUE ON UNILATERAL POSTURAL CONTROL

Measurement of postural sway is a valuable research and clinical tool that can provide information related to various central and peripheral elements of the nervous system. The present study involved modeling s ingle-limb standing as an inverted pendulum tethered to a supporting s urface by two sets of springs that simulated the stiffness of muscles spanning the joint and the inherent stiffness of the joint itself. The re arte four key elements of this model: (a) joint stiffness is greate r in the frontal plane compared to the sagittal plane (neither being a ffected by fatigue), (b) muscle stiffness is exponentially related to its extension from a resting position, (c) muscle stiffness is reduced by fatigue, and (d) an ''ankle strategy'' is used to maintain upright single-limb posture. It is concluded that an inverted pendulum model can be used to adequately predict sway frequencies and amplitudes in t he mediolateral (ML) and anteroposterior (AP) directions for single-li mb stance pre- and postfatigue. In particular, it is possible for acut e muscle fatigue to increase sway in the ML direction but not necessar ily in the AP direction.