Recently, a patient came to the clinic with acute back pain. While explaining her injury, she mentioned she was using heat to help with the pain. Then, she asked: “Well, should I be icing instead? When do you know to use heat and when do you know to use ice?”
Great question. Cold and heat application are the two main modalities physical therapists use in the clinic to help with pain. So, how do we know which one is best for the pain? It depends, but the following information helps guide me in my practice.
The main principle to understand is that placing a cold agent on a joint or muscle is abstracting heat from that body part. It is not transferring cold to the painful area.
In general, cold is used for injuries two weeks old or less, when swelling is present, for post-surgical pain and for post-rehab pain control. I use cold much more than heat. Clinically, conduction and convection are the main methods used.
Conduction: the transfer of internal energy (heat) from a region of higher temperature (skin/joint/muscle) to one of lower temperature (the ice pack) by direct contact and without movement of the cold agent.
Convection: the transfer of internal energy by the movement of water molecules across the body.
Benefits of Cryotherapy (this is not an all-inclusive list, but highlights the principles important for pain control)
- decreases blood flow to the area via vasoconstriction (blood vessel narrowing). This narrowing decreases swelling to the area. Swelling presses on the pain receptors and sends a signal to the brain: “Hey, I’m in pain down here!”. Swelling control is vital for pain resolution.
- decreases pain by decreasing nerve conduction velocity (the pain signal) to the brain and via the Gate Control Theory of Pain (see below).
- decreases muscle spasm by decreasing activity to the muscle spindle
Cold gel pack (conduction): a commercial ice pack (in a pillow case) is placed around or on the area of pain. That’s it. This the easiest and most common method of icing in the clinic and at home. Effective for: shoulders, knees, hips, back, neck. 10-20 minutes.
Ice cubes in a bag (conduction with a bonus): a bag(s) of ice (in a pillow case) is placed around or on the area of pain. Bonus: ice abstracts more heat than a gel pack because it goes through a phase change. The internal energy from the warm body part is first used to break bonds and changes ice to cold water. Now, the cold water can further abstract more heat. This is the most effective method for conduction. Effective for: shoulders, knees, elbows, ankles. 10-20 minutes.
Ice massage (conduction and convection, double whammy!): an ice-cube or frozen cup of ice is massaged over a small area of pain. Because of the direct contact and movement of the water molecules across the skin, conduction and convection (double whammy!) is occurring at the same time. This method is slightly more intense but takes less time. Ice massage is effective for smaller areas: patellar tendon, wrist, hand, foot, elbow. 5-10 minutes, until the skin starts to turn white (blanch).
Ice bath (super cold conduction): a foot or hand is placed in a bucket of ice-cold water. The increased surface area of water on skin heightens the “cold sensation” and moves the principle of heat abstraction along a little quicker. This method is great for irregular surfaces and is a more “aggressive” way to ice. Effective for: feet, ankles, hands, wrists. 10-15 minutes. Please note: the water temperature for the feet/ankles should be around 45-50 degrees F and for the hand/wrist 60-65 degrees F. It should not feel like you’re about to do the polar dip!
Clinical Guidelines for Ice
Cold modalities cause a sensation cycle in the area:
Unfortunately, most of us don’t like to ice very much and have a difficult time getting past the burn phase. Now that you know that cold is abstracting heat, try to wait out the entire cycle for optimal results.
The deeper tissue, the longer ice time. Bony areas like the knee don’t require as much as the low back. In general, the area should be cold and red to the touch and feel NUMB for a successful ice treatment. (See above for suggested time durations for each ice application.)
HEAT (Thermal therapy)
Heat application works the same as cold conduction: it is the transfer of internal energy or heat from an area of higher temperature to an area of lower temperature. It’s just the reverse. This time the hot pack is warmer than the skin and so the tissue is heated.
Benefits of Superficial Heat? (again, not an all-inclusive list)
- increases blood flow to the area via increased vasodilation (opening of the blood vessels). This increased blood flow can help with superficial lymphatic drainage and increased delivery of oxygen to the area for healing.
- increases skin temperature and tissue within ~0.5cm (it does NOT heat muscle tissue) for improved superficial connective tissue elasticity
- decreases pain by Gate Control Theory of Pain (see below)
- decreases muscle spasm by decreasing activity from the muscle spindle
Moist Hot Pack (conduction): a hot pack is placed with appropriate layers (towels, covers) over the area of pain. This is the most common application in the clinic. Moist heat is very effective (and hot!) because of the decreased ability for dissipation (heat escape), which results in increased conduction. 8-15 minutes, depending on area of body. Caution: Moist heat can cause skin burns if the heat duration is too long or not enough layers are placed between the hot pack and skin.
Dry Heating Pad (conduction): a heating pad is placed over area of pain with T-shirt layer between skin and pad. This is the most common home application and safe (unless you completely disregard the warning labels on the pad). In general, a heating pad is effective for home pain control and cheap! 10-20 minutes.
Clinical Guidelines for Heat
Heat modalities should feel warm and relaxing; it should not feel like the skin is burning. In general, the area should be warm and red for a successful heat treatment.
Gate Control Theory of Pain
Even if you choose the wrong modality (ice or heat), either of them will help relieve the pain temporarily. WHY?
It’s called the Gate Control Theory of Pain, originally explained by Melzack and Wall in 1965.
This video  is how I explain the theory to my patients (well, minus the legos. I use my hands instead). And, below, is a written explanation.
Think of a highway and two cars racing to the finish line (the finish line being your brain). The pain car can travel at two different speeds to the finish line via the Aδ fiber roadway (~50 mph) or the C fiber roadway (~30 mph). Pain is a little pokey. However, the second car can go a lot faster. Car 2 (cutaneous or skin touch) travels along the Aβ fiber roadway at ~100+ mph. It’s much faster than the pain car and will beat it to the finish line. So, when you place a cold or hot pack on the skin (or even rub the skin after a knee bang), this signal runs along the fast Aβ road and beats the Aδ and C fibers to the brain; thus, the brain perceives the skin touch, cold or heat instead of the pain. Neat, huh?
- Cold and heat are both effective for pain management
- Use cold for injuries 2 weeks or less
- When in doubt to use cold or heat: ICE, ICE BABY!
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ABOUT THE AUTHOR
Lori Duncan, DPT, MTC, CPT is a respected Physical Therapist, Manual Therapist and Pilates instructor in Lafayette, CO. Lori is passionate about preventive physical therapy and education and is a nationally recognized presenter. She can be reached at [email protected] You can also follow Duncan Sports Therapy + Wellness on Facebook  & Instagram  for more free tips and information.