Cryotherapy is better than heat for treating acute muscle strain (strength of recommendation [SOR]: C, consensus, usual practice, and expert opinion). Insufficient patient-oriented evidence exists regarding use of heat to treat acute soft-tissue injuries.
A comprehensive review of the literature revealed no studies that compare heat and cryotherapy to treat acute soft-tissue injury. Well-designed human trials of general management of acute soft-tissue injury are rare.1
Cryotherapy has been the recommended initial treatment for muscle strain for more than 30 years, based generally on expert opinion and physiological models, not clinical trials.2 Theoretically, cryotherapy controls hemorrhage and tissue edema, whereas heat enhances the inflammatory response.2
One human RCT and animal studies find benefits from cold
A 2007 review evaluated 66 publications and found only 1 randomized controlled trial conducted on humans.3 The intervention in this trial involved applying cold gel 4 times a day for the first 14 days after the injury. The control group received a room-temperature gel application; neither group was aware of the temperature differential.
The study found significant reduction in pain at rest, pain with movement, and functional disability at intervals of 7, 14, and 28 days postinjury (P<.001) among patients receiving cold-gel applications. Patients receiving cold-gel treatment also reported increased satisfaction with treatment compared with the controls. At 28 days, cold-gel treatment patients scored 71 on a 100-point satisfaction scale compared with 44 for controls (P<.001).3 Inconclusive results or significant design flaws limited the validity of all other trials cited in this review.3
Laboratory studies on rats have also demonstrated beneficial effects of cryotherapy after simulated soft-tissue injuries.4,5 One study cited a significant reduction in inflammatory cells, based on histologic examination, in 43 rats between 6 and 24 hours after trauma.4 A second study of 21 rats showed improvement in associated physiological components with cryotherapy, but no statistically significant improvement in edema.5
How cold is too cold?
Most authorities recommend empiric treatment with cryotherapy during the acute inflammatory phase—the first 24 to 48 hours after injury.6 Although not rigorously studied, some sources recommend applying cold to the involved muscle for the first 4 hours after injury at intervals of 10 to 20 minutes every 30 to 60 minutes.6
The literature focuses more on the optimal temperature for cryotherapy than on the duration and frequency of therapy.7 Temperatures below 15°to 25°C may actually result in vasodilatation rather than vasoconstriction.7