Effects of Strength and Conditioning on Maximal Isometric Strength, Motor Unit Behavior, and Concentric Isokinetic Peak Torque in Middle-School Boys'

• Rob J. MacLennan ^[1] ; Jacob A. Mota ^[3] ; Brennan J. Thompson ^[2] ; Matt S. Stock ^[1]
  1. [1] University of Central Florida

     University of Central Florida

     Estados Unidos

     
  2. [2] Utah State University

     Utah State University

     Estados Unidos

     
  3. [3] Department of Exercise and Sport Science, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina

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• Localización: Journal of strength and conditioning research: the research journal of the NSCA, ISSN 1064-8011, Vol. 36, Nº. 5, 2022, págs. 1318-1326
• Idioma: inglés
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• Resumen

  • It has long been theorized that improvements in muscle strength in young athletes are mediated by motor unit adaptations. The ability to decompose surface electromyographic signals obtained during isometric contractions now allow for such research questions to be answered. We examined changes in isometric and concentric isokinetic strength, as well as vastus lateralis motor unit behavior, after 16 weeks of strength training and conditioning in middle-school aged boys. Nine boys (mean +/- SD age = 12 +/- 1 years) participated in training. Five boys (age = 13 +/- 1 years) served as control subjects. The training subjects performed 90 minutes of high-intensity, multi-joint exercise twice per week. Assessments of unilateral maximal voluntary isometric contraction (MVIC) force of the knee extensors, concentric peak torque at velocities of 60, 180, and 300[degrees][middle dot]s-1, and vastus lateralis motor unit data during 50 and 80% MVIC tests were performed. Strength training and conditioning did not improve MVIC force. Greater training-induced strength increases were observed at faster isokinetic velocities, with a large effect size at 300[degrees][middle dot]s-1 (d = 0.813). The slopes and y-intercepts of the mean firing rate vs. recruitment threshold relationship and the action potential amplitude vs. recruitment threshold relationship were unaffected by training. Sixteen weeks of middle-school strength and conditioning did not enhance maximal isometric strength or vastus lateralis motor unit control, but improvements were observed during rapid isokinetic muscle actions. Given the lack of training (multi-joint) vs. testing (single-joint) specificity, we propose that motor unit adaptations in youth are task specific.