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Evidence Supporting Biphasic Action Of Rectus Femoris During Gait Using Ultrasound Imaging: 3130 Board #195 June 3, 2: 00 PM - 3: 30 PM.

Current evidence suggests that the eccentric action of the quadriceps during load acceptance is essential for shock attenuation. Using Ultrasound imaging (US), rectus femoris (RF) muscle thickness can be successfully quantified in real time during a gait task. PURPOSE: To characterize the RF thickness changes during the loading and terminal phase of gait. METHODS: Eighteen healthy participants (23±2yrs; 1.7±0.1m; 65.9±9.4kg) completed 3 gait trials at a self-selected pace (1.06±0.17 m/s). Lower extremity kinematics and RF thickness values were assessed concurrently during the stance phase of gait. High-speed motion analysis cameras sampling at 200 Hz were used to track marker trajectory for kinematic data. US was collected at 87 Hz with a 16-mm 5-14 MHz linear array transducer placed 60% of the distance between the anterior superior iliac spine and base of the patella. US measures were collected in a longitudinal view. The ultrasound cart traveled alongside the participant over a custom-built track system. USI images were processed on MATLAB using custom software. Time of peak knee flexion from kinematic data was used to split stance into loading phase and terminal stance. Paired t-tests were used to compare peak and average values of RF thickness during loading phase and terminal stance. Alpha level was set a priori at p<0.05. RESULTS: RF had a significantly greater (p<0.05) peak muscle thickness during terminal stance (4.8±1.98mm) than loading phase (3.9±2.23mm). However, no significant difference (p>0.05) was noted in average RF muscle thickness between terminal stance (2.8±1.10mm) and loading phase (3.2±2.10mm). CONCLUSIONS: Peak architectural changes of the RF muscle during the loading phase of stance were significantly different from the values present during the terminal stance. This finding suggests that an early and most likely stronger contraction of the RF muscle is associated with load acceptance. Our findings are the first to our knowledge to characterize RF thickness changes during stance in a healthy population. Some traumatic injuries may impair RF muscle function specifically during the loading phase, and consequently lead to joint damage. Future studies should characterize muscle properties and function in individuals with pathological conditions (e.g. posttraumatic osteoarthritis).