Article Title



P Schulken
J Fox


Penny Schulken, John Fox. Methodist University, Fayetteville, NC.

BACKGROUND: Anterior cruciate ligament (ACL) ruptures occur in up to 250,000 people per year. Neuromuscular activation imbalance between the quadriceps and hamstrings may be a significant contributor to ACL injury. It has been demonstrated that a quadriceps/hamstring ratio (QHR) closer to one reduces the risk of ACL injury. The purpose of this study was to determine the trunk angle or angles that produced a hamstring dominant QHR during a bilateral body-weight squat. METHODS: A cross-sectional design with repeated measures was used in which a sample of 10 subjects performed three repetitions of squats with trunk flexion of 15, 30, 45, and 60 degrees relative to the horizontal plane. A bilateral squat was performed until the subject’s thighs were parallel with the ground. During each squat repetition Delsys Trigno® wireless surface electrodes (Delsys Inc., Natick MA) were placed bilaterally over the biceps femoris, semitendinosus, vastus lateralis, and vastus medialis muscles. Mean EMG activity was estimated for each muscle on each leg during each repetition. The ratio of the mean activity of the vastus medialis to semitendinosus was estimated for the right and left legs (RQHRM and LQHRM, respectively). The ratio of the mean activity of the vastus lateralis to the biceps femoris was estimated for the right and left legs (RQHRL and LQHRL, respectively). The Friedman Rank Sum Test was used to evaluate the interaction of trunk angle on QHR. RESULTS: Friedman Rank Sum Test demonstrated trunk angle had a significant effect on RQHRL (Χ2=11.76, p=0.008), RQHRM (Χ2=14.04, p=0.003), and LQHRM (Χ2=13.8, p=0.003). Pairwise comparisons showed significant differences between the 15° and 60° conditions for RQHRL (p=.009), RQHRM (p=.001), and LQHRM (p=.001), and between the 30° and 60° conditions for RQHRL (p=.035). CONCLUSIONS: No trunk lean angle resulted in a hamstring dominant QHR but 60-degree trunk lean reduced the dominance of the quadriceps during squatting. The results suggest clinicians can manipulate neuromuscular activation of quadriceps and hamstrings by cueing the amount of trunk lean during squatting. This has application with the rehabilitation of individuals following ACL injury.

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