The correct answer is - the principle of overload.
Explanation:
One of the three basic principles in physical fitness is overload which suggests that an individual or species that works harder than the normal or required shows greater improvement and increases their physical fitness which leads to health benefits.
Overload means increasing physical activity by training harder to get more improvement to happen. In overload, the body performs better and adjusts in order to make it better for the future.
Thus, the correct answer is - the principle of overload.
