Final answer:
Systemic variation in training program design refers to intentionally challenging training demands by continuously increasing the intensity of the exercise.
Step-by-step explanation:
The type of variability that explains the differences in outcomes regarding the amount of weight lost in the workout program is systemic variation. This refers to the intentional variation in training program design to constantly challenge training demands. By continuously increasing the intensity of the exercise, such as lifting heavier weights, the muscles are forced to adapt and grow, resulting in greater muscle mass.