Is it possible to achieve optimal levels of tissue cooling in cryotherapy?

Background: The basic premise of cryotherapy is to cool injured tissue; however, there is much confusion around how much cooling is adequate, and how this can be achieved clinically. Objectives: Our objective was to review recent literature to determine the rate and magnitude of tissue temperature reduction with cryotherapy. Values were compared with current recommended threshold temperatures deemed necessary for optimal cold induced analgesia (skin temperature <13°C) and metabolic reduction (tissue temperature 5–15°C) after injury. Results: Current evidence confirms that cryotherapy dosage should be guided by the circumstances of injury, and clinical rationale. Optimal levels of analgesia can be achieved clinically using crushed ice for durations of 5–15 minutes. Other modes of cryotherapy may require longer durations to cool skin temperature to optimal levels, and there is further evidence that skin temperature is a poor predictor of deep tissue temperature. Based on healthy human models, it is difficult to induce large decreases in intramuscular or joint temperature, particularly in circumstances of deep tissue injury or areas of higher levels of body fat. The lowest reported superficial muscle temperature (1 cm sub-adipose) after cryotherapy is 21°C, in a lean athletic population. Reaching currently accepted threshold temperatures for metabolic reduction (5–15°C) seems unlikely. Conclusion: Future research is merited on injured human models; these should potentially focus on the clinical effectiveness of inducing more modest reductions in deep tissue temperature/tissue metabolism, after injury. Similarly, we need stronger evidence to clarify what the optimal tissue temperature reductions should be after injury, with consideration given to evolving injury models.