Mackenzie S. Kennedy, McKenzie M. Hare, Kathryn E. Southall, Kealey J. Wohlegemuth, Abbey T. Jordan, Katherine L. Ryan, Jacob A. Mota. University of Alabama, Tuscaloosa, AL.

BACKGROUND: Muscle size is thought to be associated with muscle function. However, many factors influence muscle size which may not influence function (i.e., non-contractile tissue). Image-based muscle quality, assed via B-mode ultrasound echo intensity, is thought to provide unique insight to the proportion of contractile vs. non-contractile tissue. Muscle size and quality may provide separate and unique insights to muscle function. The purpose of this study was to compare the relationships between muscle size and quality on vertical jump performance metrics. METHODS: Eight participants (mean ± standard deviation [SD] age = 20 ± 2 yrs; BMI = 25.5 ± 3.7) completed one laboratory visit to have images of vastus lateralis (VL) muscle size taken and to perform a counter movement vertical jump. Cross-sectional area images were acquired with a B-Mode ultrasound device at 50% of the length of VL while participants were supine on an exam table. Ultrasound images were downloaded and analyzed offline with an open-source imaging program, ImageJ. After scaling from pixels to cm, investigators used the polygon tool to select as much of the VL as possible. Echo intensity was calculated as the mean pixel brightness of the selected area of the VL. After a brief warm up, participants had a linear position transducer secured at the waist while they performed a counter movement vertical jump. During this task, participants were instructed to jump as high as they could and performed two jumps separated by two minutes of rest. Vertical jump average power, average velocity, and height were measured with the linear position transducer. Pearson product-moment correlation coefficients (r) were used to determine the association between muscle size and muscle quality with vertical jump performance (i.e., separate average power, average velocity, and height). RESULTS: There was a positive, statistically significant association between muscle size and vertical average jump velocity (r = 0.707, p = 0.04). However, there were no other associations found between measures of muscle size (r = 0.563, p = 0.14) or muscle quality (r < -0.58, p > 0.13) with vertical jump velocity or power. CONCLUSIONS: The results of this study suggest a strong relationship between muscle size and vertical jump velocity exists, but this may not be the case for average power or associations between muscle quality and vertical jump performance.

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