Resistance Training-induced Adaptations in Children

Resistance exercise training (RET) in children and adolescents has become a popular activity, with a growing body of evidence supporting its use. Position and consensus statements on RET for children indicate that it is safe and effective at increasing muscular strength, improving sport performance, and mitigating injury risk. Despite this evidence, there are still many unknowns with RET in children, including its mechanisms of action in enhancing muscle strength.

Neural and muscular mechanisms can improve muscle strength following RET. Neural factors include improved recruitment and firing of an individual's motor units, and muscular factors primarily include an increase in the size of the muscle (hypertrophy). In children, little is known about how these mechanisms relate to muscle strength. There is very little evidence of morphological changes following RET in children. Therefore, conventional wisdom is that children rely only on neural factors to improve strength following RET, possibly due to their lower levels of circulating androgens. Nevertheless, some studies have suggested RET-induced muscle hypertrophy in children and adolescents, indicating that with certain training protocols, and with more-sensitive research methods, children may achieve RET-induced muscle growth.

The neural mechanisms that presumably improve the muscle strength of children following RET are also largely unknown. Previously, global surface electromyography (sEMG) has been utilized to observe changes in overall muscle activation. However, this measure is unspecific and can be influenced by neural and morphological adaptations. Recent advancements in sEMG decomposition - which separates the sEMG signal into the discrete motor units it is composed of - allow for more specific neural adaptations to be assessed non-invasively. To date, this technological advancement has only been utilized in two studies to assess neuromuscular adaptations to RET in youths, with inconsistent results.

Therefore, the purpose of this study is to non-invasively assess the mechanisms of RET-induced strength increases in children performing 12 weeks of RET, compared with a non-training control group. Broadly, morphological adaptations will be assessed using ultrasound measures, while neural mechanisms will be assessed using sEMG decomposition. In addition to these primary outcomes, the effects of RET in children on cardiovascular regulation.

Procedures Participants will be required to make three pre-intervention, two mid-intervention, and two post-intervention visits to the Applied Physiology/Sympathetic Neurocirculatory Regulation Laboratories at Brock University for the completion of all testing procedures. The mid-intervention visits will be during the fourth and eighth weeks (1 session each), and the post intervention visits will be within one week following the completion of the intervention (2 sessions).