Which principle states that training must be sufficiently challenging to improve performance?

Progressive overload is the principle that emphasizes the need for training to be sufficiently challenging in order to enhance performance. It is based on the idea that in order for a person to improve their physical abilities, they must gradually increase the intensity, duration, or frequency of their training. This could involve lifting heavier weights, increasing the number of repetitions, running a longer distance, or shortening rest periods between workouts. The body needs these challenges to adapt and grow stronger, leading to improvements in strength, endurance, and overall athletic performance.

For example, if an athlete continually performs the same workout at the same intensity, their body will adapt, and improvements will plateau. By progressively overloading the muscles through increased resistance or intensity, the body is forced to adapt to the new demands, resulting in performance gains. This principle is vital in all areas of training for athletes, as it ensures continuous improvement and helps prevent stagnation in performance levels.