Cold water after a run, not after the weights

Cold water after a hard session cuts next-day soreness and the blood markers of muscle damage. Across fifty-five trials, ten to fifteen minutes at 11–15°C was the dose most likely to do it, measured against sitting still. Evidence: solid

After strength training it works against you. Cold straight after lifting blunts the muscle-building signal, and in a twelve-week trial of twenty-one men the cold-plunge group gained less muscle and strength than the group that cooled down on a bike. Evidence: decent

So: cold for the legs after the 10k, not after the squats. And never alone, never after drinking, and not at all with a heart condition or high blood pressure. Cold shock is real, and it hits in the first minute. Evidence: solid