Final answer:
The concept that describes the loss of training effects after an athlete stops exercising is known as reversibility. Individual variability accounts for the differences in weight loss outcomes among twenty people who followed the same workout routine.
Step-by-step explanation:
When an athlete stops exercise training, the training effect is quickly lost. This illustrates the concept of reversibility. Reversibility is the principle that fitness gains are lost when you stop training. It's sometimes summarized as 'use it or lose it.' The body adapts to reduced activity levels after a period of inactivity following consistent training, resulting in a decline in physical fitness.
In reference to the study of twenty people who began the same workout program, the differences in outcomes regarding the amount of weight lost can be attributed to individual variability. Factors such as genetics, diet, previous fitness levels, metabolism, and even sleep patterns can all influence how much weight each person loses.