And he has a heightened ability to recover from physical exertion, which means racing multiple times in a day is NBD.
After intense exercise, lactic acid moves into the bloodstream and becomes lactate, making the body’s lactate levels high — causing fatigue, which slows you down. The quicker you can get those lactate levels down, the better you’ll perform the next time you have to compete. Phelps reportedly produces way less lactate and therefore recovers relatively quickly and is ready to swim strong again sooner than his competitors.