Effects of localized muscle fatigue on recovery from a postural perturbation without stepping.

Several investigations have demonstrated that localized muscle fatigue (LMF) causes an increase in postural sway measures during quiet stance. Since many falls are likely the result of a postural perturbation, this study investigated the effects of LMF on balance recovery from sagittal plane postural perturbations. Thirty-two participants (16 young, 16 older) were tested. Postural perturbations were administered with ballistic pendulums before and after exercises to fatigue the lumbar extensors and plantar flexors. Measures of balance recovery were based on the center of pressure (COP) and center of mass (COM) trajectories and the maximum perturbation that could be withstood without stepping. A covariate analysis that included initial conditions at the time of the perturbation was also performed. The results demonstrated changes in the COM trajectory that were consistent with an LMF-induced decrement in the ability to recover from the perturbations without stepping. Interpretation of the COP trajectory was presented in light of the COM and indicated a modified postural control strategy following LMF.