Try it: A day or two into your soreness, when you’re done with the ice. Apply it for 20 to 30 minutes every few hours.
How it works: “After the initial inflammation has been controlled,” says Hyldahl, “heat will help increase blood flow to the area and promote healing.”
Bear in mind: A hot-water bottle will work—fill it with water that is hot to the touch, not boiling—but moist heat is ideal for sore muscles because it penetrates more deeply than dry. Try a microwavable buckwheat pillow (like Bucky Brand Hotties Body Wrap; $40, badbackstore.com) or a cotton sock filled with rice. When the pillow or sock is microwaved, the natural moisture in the grains heats up.