Hormones significantly influence body composition and fitness by regulating metabolism, muscle growth, and fat distribution. Key hormones, such as insulin, cortisol, testosterone, and growth hormone, play vital roles in how the body processes nutrients and adapts to physical activity. For example, testosterone promotes muscle mass development, while cortisol can lead to fat retention in chronic stress situations. Hormonal balance is crucial to optimizing both training and recovery, and it can affect how individuals respond to different fitness regimes, impacting overall body composition goals.