Understanding Cold and Heat Therapies

Cold and heat are natural pain relievers, both of which work on the principle of heat exchange. Any cooler object placed in direct contact with a warmer object will absorb the heat of the warmer object. Pressure, or compression, increases the effect of cold or heat therapy.

Cold restricts blood vessels and decreases circulation. 
In an injury to muscles, the blood vessels in and around the injured tissues rush oxygenated blood, nutrients, and fluids to the area, thus causing immediate swelling. At the same time, the injured cells increase their metabolism in an effort to consume more oxygen to make repairs and remove carbon dioxide and metabolic waste in the healing process.  When oxygen within the cells is used up, the cells cease functioning and die, themselves becoming metabolic waste to be removed. Blood cells and fluid from the injured cells continue to seep into spaces around the muscle, which increases bruising and swelling. Cold lowers the temperature of the damaged tissue, thereby constricting blood vessels, which aids in slowing the buildup of fluids, which slows metabolism, which in turn slows oxygen consumption, resulting in a reduction of the rate of cell damage. Cold also numbs nociceptors, nerve endings that send pain-registering impulses to the brain, reducing pain.

Because cold should be applied in 15-20-minute intervals, frozen gel packs work as well as ice packs.  Covering large areas is often more easily handled by frozen gel pads.  New injuries requiring cold therapy are best treated as soon after the injury as possible in 15-20-minute intervals for up to 48 hours, with the number of times administered depending on the severity of the injury.

If an injury is red, swollen, or inflamed, cold therapy is applicable. Never use heat therapy on a red, swollen, or inflamed injury or in the case of visible skin damage. Applying heat to newly injured tissue will have the opposite effect of that in applying cold therapy by speeding up metabolism, increasing swelling, and increasing pain.

Cold therapy works well for strains, sprains, bruises, bumps, arthritis, and other conditions that cause swelling within tissues.

Heat dilates blood vessels and stimulates circulation.
Heat causes blood vessels to expand, which increases blood flow to the injured area. This translates into an increase in oxygenated blood and the transfer of oxygen and more nutrients to the tissues at the same time as carbon dioxide and waste products are removed, thus speeding up cell recovery (i.e., healing).

Heat also loosens up chemical bonds in muscles which allow the muscles to flex and contract more easily. As the muscles becomes more pliable, tightness, soreness, and pain slowly diminish.

Muscle spasms may be caused by a lack of fluid in the cells. Because heat increases circulation, which increases fluids to the cells, heat therapy reduces muscle spasm and increases muscle elasticity, flexibility, and range of motion. It also decreases stiffness, sometimes called tightness, relaxes sore muscles, and increases comfort. 

Muscle pain can also be caused by lactic acid build up in the muscle after exercise or over-exertion, from hormonal changes and fluid accumulation in muscle tissue associated with menstrual cramps, and from pressure from fluid buildup during lactation in nursing mothers.

Heat receptors, called thermoreceptors, take priority over pain receptors when they are activated. The more activated the thermoreceptors, the greater their signal priority over pain receptors, resulting in pain signals being blocked.

Moisture is a good heat transmitter and protects the skin from drying out, making moist heat therapy better in many instances than dry heat. Never use a moist towel with an electric heating pad. However, using a moist towel between a heated gel pad and the skin will give the best transfer of heat to the body.

To prevent burns, people with poor skin sensation should not use heat therapy without knowing the temperature of the applied heat to be safe and should always apply heat with a cloth barrier between the heat pack and the skin.

Iris Floyd holds a B.S. degree in Health, Physical Education, and Recreation from Louisiana State University and is a former athlete, teacher, and coach. Finding on-site solutions for treating overheated athletes has been a quest of hers for many years. She is also President & CEO of Comfort Innovations, LLC, an inventor, writer, and published author. She can be reached at 225-603-2477 or [email protected].

Posted on Jul 20, 2018