Muscle Adaptations in Children and Adults Following Twelve Weeks of Flywheel or Weight Stack Resistance Exercise

The goal of this trial is to compare resistance exercise using traditional techniques and flywheel training to controls in healthy children ages nine to 13 and adults ages 18 to 50. The main questions it aims to answer are: * The degree of response to resistance exercise in children compared to adults regarding muscle hypertrophy and strength? * Is there a negative impact on the physis of children due to resistance exercise? Participants will be randomized to one of three groups, control, traditional resistance exercise, or flywheel. Following a baseline battery of tests, they will enter a 12-week training period, using leg press and leg extension. Additionally, post-training tests are conducted, and an eight-week detraining period commences followed by new tests. Researchers will compare children and adults and each intervention arm to see if children can achieve muscle hypertrophy, the degree and rate of changes in strength, and the potential impact on the physis.