During exercise, the body undergoes several physiological responses. Heart rate increases to supply muscles with more oxygen and nutrients, while blood vessels dilate to improve circulation. The respiratory rate also elevates to facilitate greater oxygen intake and carbon dioxide expulsion. Muscles produce lactic acid due to anaerobic metabolism, which can lead to temporary fatigue. Hormones such as adrenaline are released to enhance energy availability. These adaptations improve cardiovascular efficiency and muscle metabolism, contributing to enhanced fitness levels as one continues to exercise consistently.