The greatest-ever Olympian, in terms of medal haul, was famous for his crazy diet, which involved 33,000-42,000 kilojoules per day. But he also placed a lot of importance on sleep, and would rest up in a high-altitude sleeping chamber, which mimicked the air at 2590-2743m (over 300m higher than Mount Kosciuszko). The chamber apparently boosted Phelps’ performance by making his body work hard. Essentially, he was training even while he slept. Tiger Woods is another said to use this sleeping system.