You know what to do if you get a bad bump, a sprain, or a strain–you ice it. Doctors, nurses, therapists, and trainers will prescribe icing an injury for 20 to 30 minutes. Putting ice on an injured spot helps lessen inflammation and may have other healing benefits. It’s an effective low-tech treatment.
Scientists don’t know many of the specifics about how icing works. For example, no one knows exactly how cold the injured area needs to be to get the most benefit. And even though everyone recommends a standard 20 to 30 minutes of icing, there is little science to back that up. These researchers wondered how fat tissue affects the cooling of muscle tissue. Fat is a great natural insulator. It keeps warmth in. It also keeps cold out–including cold from an ice pack. It would make sense that people with more fat would need to apply ice longer than thin people to get the same benefit.
The researchers set out to test this theory using 47 volunteers. First, each volunteer’s skin fold thickness was measured. This was an indictor of how much fat tissue they had. Then a tiny temperature probe was inserted one centimeter into the thigh muscle. The probe read the muscle temperature throughout icing. The researchers were looking for a certain “typical” decrease in muscle temperature.
The researchers found that icing times varied dramatically depending on the amount of fat tissue. Twenty minutes with an ice pack was enough for people with skin fold measurements of less than 20 millimeters (mm). However, people with skin folds between 20 mm and 30 mm needed almost 40 minutes to get the same decrease in temperature. And people with skin folds between 30 mm and 40 mm needed a whole hour of icing.
Clearly, the standard prescription of 20 to 30 minutes of icing isn’t for everyone. The authors recommend that health care workers at least estimate the amount of fat tissue a patient has before prescribing the length of time for ice treatments.