Effect of trunk-muscle fatigue and lactic acid accumulation on balance in healthy subjects.

OBJECTIVE This study sought to determine the effects of trunk-muscle fatigue and blood lactic acid elevation on static and dynamic balance. INTERVENTION Fatigue was induced by an isokinetic protocol, and static and dynamic balance were assessed during bilateral stance using a Kinesthetic Ability Trainer. Subjects participated in a fatigue protocol in which continuous concentric movements at 60 degrees/s were performed until the torque output for both trunk flexion and extension dropped below 25% of the calculated peak torque for 3 consecutive movements. MEASURES Before and immediately after the fatigue protocol, blood lactic acid measurements and static- and dynamic-balance measurements were recorded. RESULTS An increase in lactic acid levels was detected in all subjects. According to a dependent-samples t test, significant differences in balance and lactic acid values were found after the fatigue protocol. There was no correlation between lactic acid accumulation (change between prefatigue and postfatigue levels) and balance-score differences. CONCLUSION Trunk-muscle fatigue has an adverse effect on static and dynamic balance.