Lower extremity injury is prevalent in individuals participating in sports. Numerous variables have been reported as predisposing factors; however, the predisposing effects of muscle fatigue on landing kinetics are unclear.
The purpose of this study is to investigate the effects of a single session of repeated muscle fatigue on ground reaction forces (GRF) during drop landings. Ten female (22.5±0.85 yrs) and ten male (24.1±2.6 yrs), healthy recreational athletes performed five experimental conditions. The first condition consisted of five non-fatigue drop landings (60 cm), followed by four conditions of a fatigue protocol. Fatigue was induced by a 20 second Wingate Anaerobic Test. Following each fatigue condition, participants completed two drop landings (60 cm) onto a force platform with 5 minutes of active rest between each fatigue condition. Kinetic data were used to identify peak magnitude of force for forefoot force (F1), rearfoot force (F2), anterior/posterior (AP) and medial/lateral (ML) at both F1 and F2. A mixed effect factorial ANOVA with repeated measures for GRF variables was used to determine differences between gender and within fatigue. No significant main effect was observed between genders across all GRF variables. A significant main effect was observed within the non-fatigue and fatigue conditions in respect to peak F2 force, (0.003, p<.05, η2=0.634). The greatest significant difference was shown between the first fatigue drop landing condition (F2= 7.15±2.68 bodyweights) compared to the last fatigue drop landing condition (F2=9.38±2.1 bodyweights) in respect to peak F2, (0.002, p<.05). No significant difference was observed between gender and peak F2 (0.671, p<.05) and no difference was observed across AP and ML at peak F1 and F2 across conditions. A single session of repeated conditions of anaerobic muscle fatigue induced by WAT caused an initial reduction in peak F2 followed by an increase in peak F2 across conditions. Muscle fatigue consequently alters landing kinetics, potentially increasing the risk for injury.