I get questions all time from patients who wonder whether it is better to apply heat or ice. The general rule of thumb is to apply some type of moist heat if the area is simply "dull", "stiff", "sore" or "aching" (for example, when you increase your running distance/workout). But if the area feels worse than sore or aching (more intense, perhaps "sharper" or "throbbing"), it usually indicates that the area is at least somewhat inflamed and ice (a cold pack) is usually indicated. (An exception: if your problem is primarily due to an arthritic condition, you may do better with moist heat applications.)
Apply the heat or ice (whichever you choose) typically 15-20 minutes. When applying ice, you should wrap the ice pack in a damp towel. Normal progression when using ice is a cold/stinging sensation that progresses to a burning, then to a deep aching sensation, and finally a "numb" sensation. Remove the heat or ice after about 20 minutes and briefly examine your skin-it will most likely be somewhat reddened, but should not feel as though you have a sunburn (after application of heat) or a frostbite sensation (after cold).
We always suggest to our patients that it is a good idea to gently stretch the affected area after using either ice or heat so as to regain mobility. If your pain is more severe or does not respond to the use of a hot or cold compress, you should check with your physical therapist or a medical professional before proceeding. Happy exercising!