Using ice to treat injuries is one of the oldest methods of pain control. Proven to be safe and effective at reducing swelling, relieving pain and decreasing muscle spasms, ice therapy is an easy self-care technique that anyone can administer. Every mother knows to put ice on a bruised knee after a soccer game or on a teething toddler’s tender gums. But do you really know how ice works?
Cold therapy, also known as cryotherapy, works on the principle of heat exchange. This occurs when you place a cooler object in direct contact with an object of warmer temperature, such as ice against skin. The cooler object will absorb the heat of the warmer object. Why is this important when it comes to cold therapy?
After an injury, blood vessels that deliver oxygen and nutrients to cells are damaged. The cells around the injury increase their metabolism in an effort to consume more oxygen. When all of the oxygen is used up, the cells die. Also, the damaged blood vessels cannot remove waste. Blood cells and fluid seep into spaces around the muscle, resulting in swelling and bruising. When ice is applied, it lowers the temperature of the damaged tissue through heat exchange and constricts local blood vessels. This slows metabolism and the consumption of oxygen, therefore reducing the rate of cell damage and decreasing fluid build-up. Ice can also numb nerve endings. This stops the transfer of impulses to the brain that register as pain.
Most therapists and doctors advise not to use heat right after an injury, as this will have the opposite effect of ice. Heat increases blood flow and relaxes muscles. It’s good for easing tight muscles, but will only increase the pain and swelling of an injury by accelerating metabolism.
When it comes to cooling devices, different effects will result due to the device’s ability to exchange heat. Crushed ice packs do a better job at cooling the body than chemical or gel packs, because they last longer and are able to draw four times the amount of heat out of tissue. The important difference is that ice packs undergo phase change, allowing them to last longer at an even temperature, creating a more effective treatment. Most chemical or one-time-use packs and gel packs do not undergo phase change. They quickly loose their ability to transfer heat, limiting their effectiveness to reduce swelling. Their short duration of cold is not long enough to produce numbness, also reducing their ability to relieve pain.
Cold therapy should always be used as soon as possible after an injury occurs and continued for the following 48 hours at 15 to 20 minute intervals. Remember – if you hurt yourself, you need to ice!
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