How does strength training primarily impact metabolic rate?

Strength training primarily impacts metabolic rate by increasing muscle mass, which leads to a higher resting metabolic rate. When you engage in strength training exercises, such as lifting weights, you create micro-tears in the muscle fibers, prompting the body to repair and build these fibers back stronger and larger. This process requires more energy, and as a result, it elevates the metabolic rate even when at rest.

Muscle tissue is metabolically active, meaning it burns more calories than fat tissue does, even when not exercising. Consequently, having a higher proportion of muscle can significantly boost the number of calories the body expends throughout the day, contributing to weight management and overall healthier body composition.

The other options do not accurately reflect the relationship between strength training and metabolic rate. Decreasing overall calorie expenditure contradicts the beneficial effects of strength training on metabolism. Reducing the body's oxygen requirement is not a primary effect of strength training, as physical activity typically increases the oxygen demand. Lastly, while strength training can contribute to some aspects of flexibility and balance, these are not its primary effects on metabolic rate. Thus, the increase in muscle mass is the key factor in enhancing metabolic rate through strength training.