Changes in Lower Extremity Biomechanics Due to a Short-Term Fatigue Protocol
Cortes N, Greska E, Kollock R, Ambregaonkar J, & Onate JA. Journal of Athletic Training. 2013, E-pub ahead of print. doi:10.4085/1062-6050-48.2.03
Take Home Message: As the body fatigues there may be apparent compensatory strategies employed, however, lower extremity biomechanics deteriorate as fatigue becomes greater. This may have implications for injury prevention program implementation.
Lower extremity injuries (e.g., anterior cruciate ligament [ACL], ankle sprains) tend to occur later in games or practices when athletes may be fatigued; hence, fatigue may increase susceptibility to lower extremity injuries. However, there is only limited evidence that fatigue influences lower extremity biomechanics. Therefore, the purpose of this study was to evaluate lower extremity biomechanics among female soccer players at two different fatigue severities during a functional task. Eighteen NCAA Division I female soccer players participated in motion analysis of a sidestep-cutting task and performed a functional agility fatigue protocol, which included vertical jumps, step-ups and step downs, and other activities. The authors assessed biomechanics pre-fatigue protocol as well as at 50% and 100% fatigue, which was defined by the inability to reach 90% vertical jump height during multiple sets or exertional heart rate plateau within 90% estimated maximum heart rate for 3 consecutive fatigue sets. At 50% fatigue, the soccer players used more knee flexion during landing but at initial contact they used less hip abduction, knee-adduction moment, and hip-adduction moment. When the soccer players reached 100% fatigued they continued to use less hip abduction at initial contact, less knee-adduction moment at initial contact and less hip-adduction moment at initial contact; but, now they were also using less hip flexion and knee-adduction moment during landing. Interestingly, knee flexion decreased during initial contact and during landing even though at 50% fatigue the athletes were using more knee flexion during landing.
Clinicians should understand that fatigue affects lower extremity biomechanics. Therefore, injury prevention and rehabilitation programs should take this into consideration. Interestingly, the female soccer players may have adopted compensatory strategies at 50% fatigue (e.g., increased knee flexion angles during landing). This may be due to the familiarity of the functional tasks. However, as fatigue became more severe, these compensatory movements were abandoned for movements that may increase the risk of injury (e.g., less hip and knee flexion, knee adduction). This may point to a window of vulnerability. Apparently these athletes can develop safe coping strategies up to a certain point, but they eventually will fail as fatigue gets worse. This hypothesis may suggest that injury prevention, strength and conditioning, and rehabilitation programs could help train movement strategies; but, that we cannot ignore the importance of endurance in delaying maximum fatigue. Furthermore, our programs could include training during fatigued states. It will be interesting to see clinical trials testing whether these programs delay maximum fatigue or influence lower extremity movement strategies during fatigued states. In the meantime, we need to be cognizant of the obvious influence fatigue may have on movement strategies.
Questions for Discussion: Do you use injury prevention programs at the beginning or end of practice? Do you think that there may be more appropriate times for these programs to be implemented? Has anyone had experience using cuing of biomechanics late in practices or games?
Written by: Nicole Cattano
Reviewed by: Jeffrey Driban