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Adaptations Associated With an After-School Strength and Conditioning Program in Middle-School-Aged Boys

A Quasi-Experimental Design

Thompson, Brennan J.1; Stock, Matt S.2; Mota, Jacob A.3; Drusch, Alexander S.4; DeFranco, Ryan N.5; Cook, Tyler R.5; Hamm, Matthew A.5

The Journal of Strength & Conditioning Research: October 2017 - Volume 31 - Issue 10 - p 2840–2851
doi: 10.1519/JSC.0000000000001712
Original Research

Thompson, BJ, Stock, MS, Mota, JA, Drusch, AS, DeFranco, RN, Cook, TR, and Hamm, MA. Adaptations associated with an after-school strength and conditioning program in middle-school aged boys: a quasi-experimental design. J Strength Cond Res 31(10): 2840–2851, 2017—High-intensity strength and conditioning programs aimed at improving youth performance are becoming increasingly prevalent. The purpose of this study was to investigate the effects of a 16-week after-school strength and conditioning program on performance and body composition in middle-school-aged boys. Subjects in the training group (n = 16, mean age = 11.8 years) performed 90 minutes of supervised plyometric and resistance training twice weekly for 16 weeks. A group of control subjects (n = 9, age = 12.1 years) maintained their current activity levels. Sprint speed, 5-10-5 proagility, jump height, isometric peak torque of the leg extensors and flexors, and dual energy x-ray absorptiometry-derived body composition were examined during pretesting and posttesting. Data were analyzed by performing independent samples t-tests on the absolute change scores between groups. The primary findings were that the training intervention elicited significant improvements in 20-m sprint times (p = 0.03; mean change for training group = −0.17 seconds) and body-fat percentage (p = 0.03; 2.5% absolute improvement), the latter of which was a function of reduced fat mass (p = 0.06; −0.84 kg). Between-group differences were not noted for agility, jump height, lean mass, or strength measures; however, effect sizes generally showed greater improvements for the training group. In contrast to findings in longitudinal studies performed in collegiate athletes, sprint speed may be particularly adaptable during adolescence. In addition to potentially improving sport performance, high-intensity plyometric and resistance training programs offer the added benefit of improved body composition. These programs appear less effective for agility and jump performance and do not elicit substantial improvements in muscle mass above maturation.

1Department of Kinesiology and Health Science, Utah State University, Logan, Utah;

2Department of Health Professions, University of Central Florida, Orlando, Florida;

3Department of Exercise and Sport Science, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina;

4Center for Rehabilitation Research, Texas Tech University Health Science Center, Lubbock, Texas; and

5Department of Kinesiology and Sport Management, Texas Tech University, Lubbock, Texas

Address correspondence to Dr. Matt S. Stock,

Copyright © 2017 by the National Strength & Conditioning Association.