If you train like an Olympic athlete, then stop training entirely, you become an ordinary couch potato. From Elite Athletes Can Rapidly Fall Out of Shape:
For their study, reported in the Journal of Clinical Endocrinology & Metabolism, Petibois and his colleagues followed 20 rowers who had been training for more than 10 years.During the study’s first year, all of the athletes performed endurance and weight training for about 22 hours a week, most weeks of the year. During year two, 10 athletes who wanted to retire from the sport were instructed to exercise no more than four hours each week, while the rest returned to their training regimen.
At the end of the second year, the researchers found, athletes who were not training gained enough weight and fat mass to qualify as officially out of shape. On average, their body fat increased from 12 percent of total body mass to 20 percent, while their body mass index, or BMI, reached 25-the threshold used to define “overweight.”
The rowers who stopped training rapidly lost the cholesterol benefits that their athleticism had given them. Within several weeks, their levels of “bad” LDL cholesterol went up, while concentrations of heart-healthy HDL cholesterol declined. The athletes’ triglycerides, another type of blood-fat-carrying molecule, rose by an average of about 40 percent.
The rowers were training 22 hours per week. That’s four hours a day, Monday through Friday, and two hours on Saturday. And they were 12 percent body-fat? Anyway, I’m not at all surprised that they reached a BMI of 25 — many athletes in competition have a BMI over 25. It’s not a measure of fat mass versus height; it’s a measure of body mass (including muscle) versus height. A 6′, 185-lb athlete has a BMI over 25. A 6′, 225-lb athlete has a BMI over 30: obese.