The function of the mitochondria in muscle cells is to produce adenosine triphosphate (ATP), which is the primary energy currency of cells. Mitochondria convert nutrients, specifically glucose and fatty acids, into ATP through cellular respiration. This energy is crucial for muscle contractions during physical activity, enabling endurance and overall performance. Furthermore, mitochondria play a role in regulating metabolic processes and maintaining cellular health, making them integral to an athlete's performance and recovery.