Ashley A. Herda1*, Rosemary Sisillo1, Makenzie Kerans1, Trent J. Herda2 1University of Kansas-Edwards Campus, Overland Park, KS; 2University of Kansas-Lawrence Campus, Lawrence, KS

PURPOSE: The purpose of this study was to determine if a structured exercise program would impact body or muscle composition and athletic development in elementary-aged youth. METHODS: An 8-week summer exercise program was implemented for 10young males (n=6) and females (n=4) 5-11 years old. Participants engaged in 45 minutes of various high-intensity activities two times per week over the summer months. Body mass and composition were measured with a digital scaleand2-site skinfolds (subscapular and triceps; FATSF), respectively, and muscle composition [cross-sectional area (VLCSA), thickness (VLTHICK), and echo intensity (EI)] were measured using ultrasound imaging of the right quadriceps vastus lateralis muscle and subcutaneous fat (VLFAT) of the thigh. Additionally, strength, power, and speed were measured and assessed using dominant hand handgrip (HG), broad jump (BJ), 2-poundmedicine ball throw (MBPOW), and 10meter fly sprint (SPEED10M). Three participants did not complete follow-up testing and were not included in the analyses. Paired-samples t-tests were conducted to identify change in performance and body composition variables after the 8-week intervention with an α ≤ 0.05 considered significant. RESULTS: As expected, all participants gained body mass over the 8-week program (mean diff=1.16±0.32kg, p=0.01) as they are all prepubescent and in growth flux age. Total body FATSF did not change (p=0.11). Additionally, muscle composition was altered with an increase in VLCSA (mean diff=1.04±0.30cm2, p=0.01) and VLFAT (mean diff=0.05±0.02cm, p=0.03). However, VLTHICK and EI did not change (p>0.05). For performance, MBPOW was the only variable to improve significantly (mean diff=43.2±11.54cm, p=0.01). CONCLUSION: These results indicated that 8-weeks of structured summer exercise comprising of dynamic warm-up, calisthenics, and weighted strength and power activities increased body mass and VL muscle cross-sectional area without a transient change in lower-body performance in prepubescent youth. The marginal changes (+3.8%) in body mass may be due to their growth stage. However, FATSF did not change and the 15.1% improvement in upper-body power may imply training impacted athletic development more so than growth stage.

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