Mandy Parra1, Jonathan Miller1, Melani Kelly1, Trent Herda1 1Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, KS

PURPOSE: Echo intensity (EI) is a measure of muscle composition and muscle size (CSA) is directly related to maximal strength (MVC). The purpose of this study is to examine the relationship between muscle composition and maximal strength in overweight and normal weight college aged individuals in a weight-bearing and non-weight bearing muscle. Furthermore, to determine if correcting for EI is necessary when considering muscle size and maximal force generation capabilities. METHODS: Sixteen individuals, eight normal weight (five males and three females, mean ± SD, age=20.8±2.3years, BMI=22.21±2.4 kg/m2) and eight overweight (five males and three females, age=20.3±2.3 years, BMI=29.65±6.05 kg/m2)volunteered for the study. Participants visited the lab on three separate occasions, separated by at least 24 hours. Visit one consisted of ultrasound measurements of the vastus lateralis (VL)and the first dorsal interosseous (FDI), and familiarization to MVC protocols. Ultrasonography was used in B-mode to measure anatomical CSA subcutaneous fat thickness (SF)and EI of the VL and FDI. For the leg extensors, isometric MVCs were performed on an isokinetic dynamometer. The abduction of the FDI was isolated for the MVCs and measured on a force transducer. During the experimental trials, participants performed three MVCs with strong verbal encouragement for motivation. The highest peak torque or force output was used for further analysis. Pearson product moment correlations were performed between CSA and CSA corrected for EI (CSA/EI) with MVC for the VL and the FDI. RESULTS: There was a significant relationship between CSA/EI and MVC for the VL and FDI (p=0.035, r=0.529; p=0.009, r=0.626), however, there was no significant relationship with CSA for the VL or FDI(p=0.255, r=0.303; p=0.058, r=0.483). CONCLUSIONS: EI is a measure of non-contractile tissue and correlates with adipose tissue in the muscle. Significant positive correlations were present when CSA was corrected for EI for the VL and FDI with no significant correlations present between CSA and MVC. Therefore, individuals with poorer skeletal muscle composition (greater adipose tissue) may be weaker regardless of muscle size and function. Adipose tissue in the muscle may have a deleterious effect on maximal strength.

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