What theory states that a training program must include a maintenance plan to retain training gains?

The theory that asserts a training program must include a maintenance plan to retain training gains is the principle of reversibility. This principle indicates that once a person stops exercising, the physiological adaptations gained from training—such as increased strength, endurance, or muscle mass—begin to diminish. Essentially, if someone ceases their training regimen, they will revert back towards their baseline level of fitness over time.

This understanding emphasizes the importance of incorporating strategies to maintain the improvements achieved through training, such as continuing a reduced but consistent level of activity, alongside a structured maintenance plan. By acknowledging this principle, fitness professionals can better program their clients' training regimens to ensure lasting results and prevent detraining.

The other concepts, while significant, do not focus on the retention of training gains after cessation of activity: the principle of progression deals with gradually increasing the difficulty of workouts; the principle of overload emphasizes the need to challenge the body beyond its current capabilities for improvement; and the principle of variation pertains to changing workout components to enhance engagement and prevent plateaus.