Muscle fatigue and neuromuscular knee valgus in strong versus weak young female athletes

Abstract: Background. Knee injuries such as anterior cruciate ligament injuries (ACL) are common in young female athletes resulting in great medical and personal costs. Both knee valgus and muscle fatigue has been reported to increase the risk of injury, while strength training has been used to reduce the occurrence of knee valgus and injury. However, few data exist on the impact of muscle strength and fatigue on knee valgus. Aim. The study aimed at investigating whether muscle strength affects the presence of knee valgus and if fatigue affects knee valgus differently depending on the level of muscle strength in young female athletes. Methods. Twenty young female athletes, mean age 18,15 (±0,79) years, participated in this study. A unilateral drop jump, video analysed in 2-dimensional, was used to evaluate knee valgus and a one Repetition Maximum (1RM) in squat was used to determine the level of muscle strength. A fatigue protocol was used to achieve muscle fatigue before another unilateral drop jump was performed. The subjects were dichotomised, by the 1 RM according to the median, to analyse ‘weak’ versus ‘strong’ females. Both the right leg (RL) and the left leg (LL) were measured before and after fatigue. Results. No significant differences, in the degree of knee valgus, were found between strong and weak group before (RL, p=0.6, LL, p=0.11), or after (RL, p=0.97, LL p=0.36) fatigue. There was also no significant difference in how fatigue affected knee valgus between strong and weak group (RL, p=0.5, LL, p=0.38). Conclusion. The present study suggests that there is no difference in knee valgus between strong and weakfemale athletes. In addition, fatigue does not seem to have an impact on knee valgus in neitherstrong nor weak females. This study has limited number of subjects and further studies are needed.