Endurance training protects muscle damage by increasing the levels of _____.

• A. Endogenous antioxidants
• B. Exogenous antioxidants
• C. Antioxidant enzymes from diet
• D. Structural proteins that resist oxidative stress

Answer: (D)

Endurance training strengthens the muscle’s own antioxidant defenses. Regular prolonged exercise increases the production of reactive oxygen species, and the muscle adapts by boosting its internal antioxidant system, raising levels of endogenous antioxidants and antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase. This enhanced capacity helps neutralize ROS more effectively, reducing oxidative damage to muscle cells during future workouts. Diet-derived antioxidants come from outside the body and aren’t inherently increased by training, and enzymes from the diet aren’t produced by the body in response to training. Structural proteins aren’t the primary factor in protecting against oxidative stress; the key adaptation is the upregulated endogenous antioxidant system.