It's common in serious athletes to see enlarged hearts. The body adapts to the need for more oxygen by creating thicker walls in the heart. But researchers out of France recently took a look at the hearts of Tour de France cyclists and found that their tickers were 20 to 40% larger than average. Though they can't say for sure whether the bikers' hearts were larger than average to begin with, after cyclists retired, their hearts did lose about 25% of their mass, even though the athletes stayed in excellent shape. Tour de France participants are among athletic elite, so seeing how their bodies adapt to strenuous exercise is pretty interesting!