Effects of fatigue on frontal plane knee motion, muscle activity, and ground reaction forces in men and women during landing

Women tear their anterior cruciate ligament (acl) 2-8 timesmore frequently than men. frontal plane knee motion can producea pathological load in the acl. during a state of fatiguethe muscles surrounding the knee joint may lose the ability toprotect the joint during sudden deceleration while landing. thepurpose of this study was to investigate the effects of fatigue andgender on frontal plane knee motion, emg amplitudes, andgrf magnitudes during drop-jump landing. pretest-posttestcomparison group design was used. twenty-six volunteers (14women; 12 men; mean ± standard deviation age = 24.5 ± 2.7yrs; height = 1.73 ± 0.09 m; mass = 74.3 ± 11.8 kg) participatedin the study. knee frontal plane ranges of motion and positions,ground reaction force peak magnitudes, and surface emg rmsamplitudes from five lower extremity muscles (vastus medialis,vastus lateralis, medial hamstring, lateral hamstring, and lateralgastrocnemius) were obtained during the landing phase of adrop-jump. manova and anova indicated that peak grfsignificantly (p < 0.05; 2.50 ± 0.75 bw vs. 2.06 ± 0.93 bw)decreased during fatigued landings. no other variables exhibiteda fatigue main effect, although there was a significant (p < 0.05)fatigue by gender interaction for the frontal plane range of motionfrom initial contact to max knee flexion variable. follow-upanalyses failed to reveal significant gender differences at thedifferent levels of fatigue for this variable. additionally, novariables exhibited a significant gender main effect. singlesubject analysis indicated that fatigue significantly altered frontalplane knee motion, peak grf, and emg in some subjectsand the direction of differences varied by individual. fatiguealtered some aspects of landing performance in both men andwomen, but there were no gender differences. additionally, bothgroup and single subject analyses provided valuable but differentinformation about factors representing neuromuscular controlduring drop-jump landing.