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DuPont, Corey E.1; Chmielewski, Terese L.2; Kawaguchi, Jeffrey3; Mizner, Ryan L.1
1Eastern Washington University, Spokane, WA.
2University of Florida, Gainesville, FL.
3Eastern Washington University, Cheney, WA.
PURPOSE: The step down task has been used by some as a screening tool to identify female athletes who may be at high risk for knee injury due to poor control of limb alignment. While it is used clinically, there is still little known regarding what neuromuscular factors are involved in control of limb posture during this task. The purpose of our study was to examine LE orientation and coordination as well as identify muscular control strategies during a single leg step-down task in female athletes.
METHODS: Twenty-five female collegiate athletes (age=20 ± 1, ht=1 .73m ± 0. 1, wt=75kg ± 9) participated in kinetic and kinematic analysis of a step down task (8 inches). Preamplified electrodes (Motion Lab Systems) were used to collect surface EMG of the gluteus medius and maximus, lateral quadriceps, lateral hamstrings, and soleus musculature was also recorded and normalized to peak activity during MVIC. The relationship between peak joint positions during step down and peak normalized muscular recruitment and joint position was assessed using Pearson Correlation Coefficients (alpha = 0.05).
RESULTS: The quadriceps muscle had the largest normalized peak activation (58% MVIC) followed by the soleus (39%), hamstring (30%), gluteus medius (23%) and finally gluteus maximus (15%). Peak hip flexion was negatively related to calf activation (r=−0.38) while peak knee flexion was positively related to gluteus medius activation (r=0.51). Peak ankle dorsiflexion (DF) was positively related to both hamstring (r=0.41) and soleus (r=0.53) activity. Peak hip flexion related positively to knee flexion(r=0.49) and negatively to DF (r=0.39). Peak knee flexion related positively to both hip(r=0.491) and ankle DF (r=0.415).
CONCLUSION: The step down task elicited surprisingly low activation from the proximal muscles and relatively greater recruitment from the quadriceps and soleus. Utilization of greater hip flexion motion during step down was associated with less utilization of ankle DF and resultant lower calf activation. A knee flexion with hip flexion dominant strategy results in greater gluteus medius activation and less calf while knee flexion coupled with ankle DF elicits more of a response from the calf and hamstring muscles. Funded by State of Washington HEC Board Grant.
©2007The American College of Sports Medicine
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