Cortisol is a hormone produced by the adrenal glands in response to stress. Its importance for fitness lies in its role in regulating metabolism, immune function, and the body’s response to stressors. While cortisol can aid in energy mobilization, chronic high levels can hinder physical performance, increase fat storage, and lead to muscle loss. Managing stress levels through exercise, mindfulness, and proper nutrition is essential for maintaining balanced cortisol levels and optimizing overall fitness outcomes.