Cold Therapy vs. Heat Therapy for Injuries: Which one?

It’s the age old question relating to sports injuries---“Should I apply heat therapy or cold therapy?” I’m actually surprised at the confusion surrounding this issue. The answer is almost always cold therapy. Heat therapy can actually be detrimental to tissue healing in many cases. To clarify specific issues surrounding this topic, I’ll discuss the appropriate application of both modalities here.
Sports injuries are the result of trauma to your tissue. It could be externally applied by a collision with an opponent or inanimate object. It can also occur independent of an outside source---such as when you role your ankle or twist your knee while changing directions. 
Trauma to your tissue sets off a physiologic process known as inflammation. As part of the inflammatory process, your body sends specialized cells and proteins to seal off the injured area, destroy damaged tissue and keep out bacteria. This can become problematic as, left unchecked, inflammation can destroy healthy tissue and create a bigger problem than you started with. To prevent this, it is crucial that you minimize inflammation as soon as possible.
Application of ice, more properly known as cryotherapy, decreases the temperature of injured tissue. This helps diminish pain, slow down muscle metabolism, and minimize muscle spasm. As a result---and here’s the key---the inflammatory process is decreased which aides in tissue recovery after trauma. Introduction of heat to the area will have the opposite effect. It increased blood flow to the area and can actually accelerate the inflammatory process in acute injuries. Therefore, any time there is an acute sport injury with swelling or inflammation present, heat is not appropriate.
The application of cold therapy treatment is different depending on the acuity of the sports injury in question. Ice applied right after the injury occurs reduces muscle metabolism and decreases the degree of tissue damage due to inflammation. Later, when the sports injury is in its sub-acute phase, the primary purpose of cold therapy is to relieve pain to help facilitate exercise and activity tolerance.
Hopefully, by now I’ve convinced you to use cold therapy with your acute or sub-acute sports injury. Mode and duration of cold therapy is important. Large, flexible gel ice packs that can surround the joint provide superior skin cooling effects when compared to rigid ice packs. Research articles recommend anywhere from 10-20 minutes 2-4 times a day up to 30-45 min every two hours. I typically suggest that more severe injuries and post-operative patients apply ice more frequently but for the average sports injury 10-20 minutes 2 times a day, especially after activity, is adequate for cold therapy.
Despite its lack of applicability to acute injuries, heat therapy is not without utility in treating certain types of injuries. Heat therapy can be applied for chronic issues such as muscle or joint stiffness or soreness. Heat therapy can also help relax muscles or decrease muscle spasms. In these cases, heat therapy is best applied before exercise to promote blood flow and prepare tissue for use. 
Heating pads or hot packs are good heat therapy treaments but I recommend moist heat for maximum efficacy. Try using a hot, wet towel to wrap the area in question. Safely apply moist heat therapy for 15-20 minutes at a time and make sure that you have several layers between your skin and the heating source to avoid burns. Heat therapy should not be applied after exercise. Even with chronic injuries, ice is the better choice after activity.
Cold therapy and heat therapy both have useful applications when dealing with sports injury. Make sure you select the correct modality for your injury and always apply it safely. Cold temperatures can burn your skin just as easily as hot temperatures if not applied properly. If you develop a fever or your sports injury does not improve after a reasonable time, be sure to see your physician to rule out something more serious.