Final answer:
The undulating periodization model varies volume and intensity each workout or week to prevent stagnation, promote muscle growth, and improve overall performance.
Step-by-step explanation:
The periodization model that varies volume and intensity each workout or week is known as the undulating periodization model. This model involves alternating between high-volume, low-intensity workouts and low-volume, high-intensity workouts. The variation in volume and intensity helps to prevent stagnation, promote muscle growth, and improve overall performance.