Neuromuscular fatigue and tibiofemoral joint biomechanics when transitioning from non-weight bearing to weight bearing.
Schmitz RJ, Kim H, and Shultz SJ. J Athl Training. 2015. 50(1): 23-29.
Take Home Message: Following a fatiguing exercise protocol, participants showed increased anterior tibial translation, compressive force, and knee flexion range of motion during the transition from non-weight-bearing to weight-bearing. This illustrates an inability of the lower extremity muscles to stabilize the knee joint.
An athlete is at greater risk for a noncontact injury, such as an anterior cruciate ligament (ACL) tear, later in games. While it is believed that fatigue may play a role in ACL injury, little evidence exists to support this. If this can be verified, clinicians may be able to identify strategies to better train athletes to stabilize the knee joint in a fatigued state and limit the risk of sustaining an ACL injury. Therefore, Schmitz and colleagues completed a cross-sectional study to assess the impact of a fatiguing exercise protocol on tibiofemoral biomechanics when transitioning from non-weight-bearing to weight-bearing. The researchers recruited 10 participants (5 male, 5 female, age ~25 years) with no history of knee injury to the dominant leg. All participants were further screened by a certified athletic trainer to ensure there was no lower limb dysfunction. All participants wore motion analysis sensors and were placed into the Vermont Knee Laxity Device to measure anterior tibial translation when a force of 40% body weight was applied to the bottom on the foot, which simulated weight bearing. Three successful trials were obtained before and after a fatiguing exercise protocol. Fatiguing was accomplished by having the participant perform a repeated leg press of 60% of their body weight for 15 repetitions with 10 seconds rest until the participant could no longer complete a full set. Overall, during initial weight-bearing the authors found a 6% increase in compressive force, a 28% increase in knee flexion range of motion, and a 22% increase in anterior tibial translation after the fatiguing exercise compared with before.
The authors present interesting data to support the concept that knee joint biomechanics are altered in a fatigued state. Hence, an individual is less able to stabilize his/her knee during initial weight-bearing when the lower extremity is fatigued. This suggests that physically active individuals may be at an elevated risk of ACL injury near the end of activity as the muscles in the lower extremity are less able to stabilize the joint. Before this is confirmed though more research should be completed in a larger cohort as well as to take into account participant activity levels to better understand the effects that training may have on this phenomenon. While more work may be needed this study may be valuable to clinicians in the future in terms of activity modification, bracing, and training regiments to further increase knee joint stability while fatigued. Until this can be completed clinicians should be observant for faulty mechanics in practice and competitions when fatigue is likely. Furthermore, clinicians may wish to discuss how to handle fatigued athlete with their sports medicine team to discuss if the athlete in question should be removed from activity, and if so who is responsible for making such a decision.
Questions for Discussion: Have you seen a correlation between ACL injury and fatigue status of your athletes? If so, do you intervene when you feel an athlete is fatigued and exhibiting faulty joint mechanics?
Written by: Kyle Harris
Reviewed by: Jeffrey Driban
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