Effects of Fatigue and Recovery on Knee Mechanics during Side-Step Cutting

TSAI, L., S. M. SIGWARD, C. D. POLLARD, M. J. FLETCHER, and C. M. POWERS. Effects of Fatigue and Recovery on Knee Mechanics during Side-Step Cutting. Med. Sci. Sports Exerc., Vol. 41, No. 10, pp. 1952-1957, 2009. Introduction: Changes in knee mechanics immediately after a fatiguing bout of exercise are thought to place an individual at a greater risk for anterior cruciate ligament (ACL) injury. However, the recovery time required to restore normal knee kinetics and kinematics after fatigue has not been established. Purpose: The purpose of this study was to examine knee mechanics during side-step cutting immediately after a fatigue protocol and after 20 and 40 min of rest. Methods: Knee kinematics (eight-camera system Vicon 612; Oxford Metrics, Oxford, United Kingdom) and kinetics (AMT1 force platform; AMT1, Newton, MA) of 15 female recreational athletes were recorded during a side-step cutting task. Data were obtained at four different time points: 1) before a fatigue protocol, 2) immediately after the fatigue protocol, 31) 20 min after the fatigue protocol, and 4) 40 min after the fatigue protocol. Peak knee joint angles and knee joint moments in the sagittal, frontal, and transverse planes were identified during the deceleration phase of the cutting task. One-way ANOVA with repeated measures were used to compare variables among the four time points. Results: Peak internal knee adductor moments (external knee valgus moments) and peak knee internal rotation angles were significantly greater after fatigue and remained elevated at 20 and 40 min after fatigue. Peak knee abduction (valgus) angles immediately after the fatigue protocol were significantly greater but returned to prefatigue levels after 20 min of rest. The fatigue protocol had no influence on any other of the variables examined. Conclusions: Fatigue resulted in changes in knee mechanics that are thought to be associated with ACL injury. Forty minutes of recovery was not sufficient in restoring knee mechanics to prefatigue levels.