A client's workout record shows changes in exercise volume and intensity over time. What training concept is being demonstrated?

Specificity refers to the principle that adaptations are specific to the type of training performed, not to planned variation in volume and intensity over time.

Overtraining describes a maladaptive state caused by excessive training load without adequate recovery, not a structured planning concept.

Reversibility describes the loss of fitness adaptations when training stimulus is reduced or removed, not the planned progression of a program.

Periodization involves organizing a training program into distinct phases or cycles - such as mesocycles and macrocycles - during which volume and intensity are deliberately varied to drive progressive adaptation while managing fatigue. A workout record showing these changes over time is a direct demonstration of periodization in practice.