Final answer:
Gains in fitness such as strength, endurance, and muscle mass can start to diminish within 1-2 weeks of inactivity. While this can vary by individual, re-gaining lost progress can be quicker due to muscle memory.
Step-by-step explanation:
In the context of fitness and exercise, the term gains typically refers to improvements or progress made in physical strength, muscle mass, endurance, or overall fitness levels. When considering the reversibility of these gains, it is generally understood that if an individual stops exercising, the progress that has been made can begin to diminish. Specifically, the losses typically become noticeable within 1-2 weeks, which is option a). The rate of loss can vary depending on the individual's previous training levels, physiology, and how long they have been inactive.
It is important to recognize that while some loss of gains can occur relatively quickly, re-establishing these gains can often be achieved more speedily than when starting from scratch, due to muscle memory. Consistency in training is key to maintaining progress and minimizing the effects of reversibility.