Which of the following factors is essential to include in a fitness regimen according to studies about metabolic rate?

Strength training is vital in a fitness regimen, particularly concerning metabolic rate. Research has shown that, unlike cardio training, which primarily burns calories during the activity, strength training has the added benefit of increasing muscle mass. Muscle tissue is metabolically active, meaning it requires more energy to maintain than fat tissue, thereby enhancing the resting metabolic rate.

Incorporating strength training into a fitness routine not only helps build lean muscle but also contributes to maintaining muscle mass during weight loss, which is crucial for sustaining metabolic health. Moreover, after engaging in strength training, the body continues to burn calories at an elevated rate through the process of muscle recovery and repair, known as excess post-exercise oxygen consumption (EPOC).

While cardiovascular training can improve heart health and overall endurance, and flexibility exercises like yoga can enhance range of motion and reduce injury risk, neither directly contributes to increasing metabolic rate as effectively as strength training does.