Fitness can be improved by training more than normally do.*1 pointProgressionOverloadSpecificityReversibility

The question presents four concepts related to fitness training: Progression, Overload, Specificity, and Reversibility. To determine which concept relates to improving fitness by training more than one normally does, we can analyze each option.

1. Progression refers to the gradual increase of stress placed upon the body during exercise training. It is vital for improving fitness levels over time but is not specifically about training more than usual.

2. Overload is the principle that states to improve fitness, one must exercise at a level greater than usual. This involves increasing the intensity, duration, or frequency of workouts beyond what the body is accustomed to.

3. Specificity relates to the idea that training should be relevant and appropriate to the sport or fitness goal for optimal performance. While specificity is crucial, it does not directly address the increase in training volume or intensity.

4. Reversibility refers to the concept that fitness gains can be lost if training ceases. This doesn't align with the idea of training more than normal.

Given these definitions, the best answer is:

Final Answer

Overload is the correct concept that relates to improving fitness by training more than normally do.