EXTREME ATHLETES: RISKS AND REWARDS Our body can endure a lot more than you think. It can grind through a mountain ultramarathon or pedal across a continent. But there's a catch: when you push it to these extremes, things start happening beneath the surface—some of them inspiring, others a little alarming. Ultra-endurance athletes are basically running ongoing experiments on themselves. A marathon? That's just stretching their legs. These are the folks signing up for 24-hour runs, week-long cycling odysseys, and swims that make the English Channel look like a backyard pool. Their bodies adapt in ways that are as fascinating as they are sometimes worrisome. Let's talk about the heart. When you train at this level, your heart doesn't just get fitter—it actually changes shape. It grows larger, its walls thicken, and it pumps more efficiently. Doctors call this "athlete's heart." Most of the time, it's harmless, just the body tuning itself for enduranc...