Marissa L. Bello1, Abigail N. Shilling2, Morgan R. Wood3, JohnEric W. Smith3. 1University of Alabama at Birmingham, Birmingham, AL. 2Stetson University, Deland, FL. 3Mississippi State University, Mississippi State, MS.

BACKGROUND: Favorable alterations in body composition have been shown to positively impact athletic performance. Varying loading intensities of resistance training may influence the magnitude of body composition changes. The purpose of this study was to assess and determine changes in body composition and muscle thickness following nine weeks of high- or low-load whole-body resistance training. METHODS: Seventeen recreationally trained males (Mage = 20.4 ± 2.7 yrs) were recruited for this study. Participants were randomly assigned to one of two training groups: 30% (n=9) or 85% (n=8) of predicted 1-repetition maximum (1-RM). Participants completed three sessions per week of a whole-body workout (back squat, deadlift, bench press, T-row, bicep curls, skullcrushers) over nine weeks. Sessions consisted of three working sets to failure for each exercise at the prescribed percentage. Bioelectrical impedance analysis was used pre- and post-training program to assess body mass (BM), body fat percentage (%BF), and skeletal muscle mass (SMM). Ultrasound was used to assess muscle thickness at five locations: biceps, triceps, chest, quadriceps, and hamstrings. A paired T-Test was used to assess changes in each body composition measure from pre- to post-training. Significance was set a-priori at P<0.05. RESULTS: There were significant differences between groups with greater increases in the 85% group for SMM (2.6±1.6 vs 0.24±2.58 kg; P=0.041) and triceps thickness (0.44±0.34 vs 0.08±0.36 cm; P=0.035), with no significant group differences in any other measure. When collapsed across groups, there were additional significant changes in muscle thickness for biceps (P<0.001) and hamstrings (P=0.031). CONCLUSIONS: The difference in loading of resistance training in this study had a significant effect on SMM, with the 85% group showing greater increases. The training overall produced hypertrophy in a majority of the muscles measured, although it should be noted the 85% group demonstrated greater increases in muscle thickness overall with the only exception being the quadriceps. The results of this study indicate training at either lower or higher loads are both beneficial for increasing SMM and hypertrophy. Despite these findings, %BF was not significantly altered. Future research should incorporate other testing variables that may further favorably impact body composition and distinguish any additional loading differences.

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