Final answer:
Workout variability includes intensity, duration, frequency, and type of exercise. Individual outcomes from identical workout programs can differ due to genetic factors, recovery, nutrition, muscle composition, and metabolism rates.
Step-by-step explanation:
The factors that can be varied in a workout include intensity, duration, frequency, and the type of exercise. For instance, a workout program might vary in intensity from low intensity or skill-based activities to endurance programs consisting of 1-3 hours per day of moderate to high-intensity exercise. The outcomes of such workouts can differ significantly among individuals due to several factors. These could range from genetic differences, such as the proportions of slow-twitch and fast-twitch muscle fibers, affecting muscular endurance and strength, to external factors such as nutrition and rest, which can influence the effectiveness of the workout and the occurrence of issues like delayed onset muscle soreness (DOMS).
Regarding the question about 20 people following the same workout program, differences in weight loss outcomes can be attributed to individual variability, including possibly genetic factors, recovery practices, nutrition, and other lifestyle elements. Variations in muscle composition, such as slow-twitch and fast-twitch fibers, metabolism rates, and adherence to the workout routine outside of the observed sessions might also contribute to varying results.