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.