Which principle suggests that an athlete must train specifically to improve in that area?

The principle that suggests an athlete must train specifically to improve in a particular area is the principle of specificity. This principle states that the body adapts to the specific demands placed upon it during training. In essence, to enhance performance in a certain skill or physical capacity, the training regimen should be closely aligned with that skill or capacity. For example, a swimmer should focus on swimming drills to improve their swimming performance, as opposed to running or cycling, which would not directly translate to swimming abilities.

This principle emphasizes the importance of tailoring workouts to meet the specific requirements of the desired outcome—whether it be strength, endurance, speed, flexibility, or skill-related performance. It helps athletes understand that to excel in their sport, their training must closely resemble the environment and demands they will face during competition.