Try it: Over the next few days.
How it works: The salts (sold at drugstores) contain magnesium sulfate, a mineral that works as a subtle muscle relaxant. “The deep soak also helps get blood flowing to sore muscles,” says Ashley Borden, a personal trainer in Los Angeles. Sprinkle a cup of Epsom salts into the bathwater, which should be “as hot as you can stand it,” says Borden.
Bear in mind: To stay hydrated and not get overheated, try drinking a glass of cold water in the tub.