Despite the fact that scientific research on contrast water therapy is somewhat inconclusive, it is still widely used by athletic trainers as a means of speeding post-workout recovery and treating injury. This, says Julieta Guzman, a certified athletic trainer in California, is because “clinically, it works.”
The idea behind contrast water therapy (alternating between hot and cold water immersion) is that the cold water constricts blood vessels and helps to flush out waste products, such as lactic acid. The warm water, on the other hand, increases circulation and improves the healing process.
Interestingly, when treating an injury such as a sprain or a strain, the athlete begins and ends in warm water. But for workout recovery they begin and end in cold water. In either case, though, Julieta reports that with contrast therapy, “athletes feel an overall reduction in muscle soreness.”