The nutrient primarily responsible for muscle repair after exercise is protein. Consuming adequate amounts of protein post-workout supplies the necessary amino acids needed for recovery and muscle synthesis. Protein helps rebuild damaged muscle fibers incurred during intense exercise, promoting growth and adaptation. It's beneficial for athletes and regular exercisers to consume high-quality protein sources such as lean meats, dairy, legumes, and nuts within the recovery window. Adequate protein intake contributes to improved performance and reduced risk of injury.