Muscle mass significantly affects metabolic rate because it consumes more energy at rest compared to fat tissue. Individuals with higher muscle mass tend to have a greater BMR (basal metabolic rate), leading to increased calorie expenditure. This shift in metabolic activity not only aids in weight maintenance but also enhances overall body composition and energy levels. Therefore, incorporating strength training to build muscle can have long-lasting effects on metabolism and weight management, making it a crucial component of any fitness regimen focused on health improvement.