Final answer:
The periodization model that involves varying volume and intensity each workout or week is undulating periodization. This method contrasts with linear periodization by incorporating frequent changes to promote continuous improvement. Individual variability in exercise outcomes is due to differences in biology, diet, metabolism, and lifestyle.
Step-by-step explanation:
The periodization model that varies volume and intensity each workout or week is known as undulating periodization. This approach to training is characterized by frequent changes in the training variables to prevent plateaus in performance and promote continued progress. In contrast, linear periodization typically involves progressively increasing the intensity of workouts over time while decreasing volume, and other types do not have the same frequent variations.
As for the 20 people who began the workout program with different outcomes in weight loss, the variations in results could be due to individual biological differences, dietary habits, metabolism rates, and even sleep patterns. Although they engaged in the same pattern of physical exercise, individual responses to exercise can greatly differ.