Lower extremity fatigue, sex, and landing performance in a population with recurrent low back pain.

CONTEXT: Low back pain and lower extremity injuries affect athletes of all ages. Previous authors have linked a history of low back pain with lower extremity injuries. Fatigue is a risk factor for lower extremity injuries, some of which are known to affect female athletes more often than their male counterparts.
OBJECTIVE: To determine the effects of lower extremity fatigue and sex on knee mechanics, neuromuscular control, and ground reaction force during landing in people with recurrent low back pain (LBP).
DESIGN: Cross-sectional study.
SETTING: A clinical biomechanics laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty-three young adults with recurrent LBP but without current symptoms. INTERVENTION(S): Fatigue was induced using a submaximal free-weight squat protocol with 15% body weight until task failure was achieved. MAIN OUTCOME MEASURE(S): Three-dimensional knee motion, knee and ankle moments, ground reaction force, and trunk and lower extremity muscle-activity measurements were collected during 0.30-m drop vertical-jump landings.
RESULTS: Fatigue altered landing mechanics, with differences in landing performance between sexes. Women tended to have greater knee-flexion angle at initial contact, greater maximum knee internal-rotation angle, greater maximum knee-flexion moment, smaller knee-adduction moment, smaller ankle-inversion moment, smaller ground reaction force impact, and earlier multifidus activation. In men and women, fatigue produced a smaller knee-abduction angle at initial contact, greater maximum knee-flexion moment, and delays in semitendinosus, multifidus, gluteus maximus, and rectus femoris activation.
CONCLUSIONS: Our results provide evidence that during a fatigued 0.30-m landing sequence, women who suffered from recurrent LBP landed differently than did men with recurrent LBP, which may increase women's exposure to biomechanical factors that can contribute to lower extremity injury.