Objectives: To determine the impact of the application of cryotherapy on nerve conduction velocity (NCV), pain threshold (PTH) and pain tolerance (PTO). Design: A within-subject experimental design; treatment ankle (cryotherapy) and control ankle (no cryotherapy). Setting: Hospital-based physiotherapy laboratory. Participants: A convenience sample of adult male sports players (n = 23). Main outcome measures: NCV of the tibial nerve via electromyogram as well as PTH and PTO via pressure algometer. All outcome measures were assessed at two sites served by the tibial nerve: one receiving cryotherapy and one not receiving cryotherapy. Results: In the control ankle, NCV, PTH and PTO did not alter when reassessed. In the ankle receiving cryotherapy, NCV was significantly and progressively reduced as ankle skin temperature was reduced to 10˚C by a cumulative total of 32.8% (p,0.05). Cryotherapy led to an increased PTH and PTO at both assessment sites (p,0.05). The changes in PTH (89% and 71%) and PTO (76% and 56%) were not different between the iced and non-iced sites. Conclusions: The data suggest that cryotherapy can increase PTH and PTO at the ankle and this was associated with a significant decrease in NCV. Reduced NCV at the ankle may be a mechanism by which cryotherapy achieves its clinical goals. C ryotherapy has been accepted for decades as an effective, inexpensive and simple intervention for pain management after many acute sport injuries.1 2 It is widely believed that the therapeutic application of cryotherapy leads to a reduction in pain and swelling, but the physiological basis for this effect is still incompletely understood.3 4 Saeki 5 and other authors concluded that pain relief with cold application could be due to many mechanisms including altered nerve conduction velocity (NCV), inhibition of nociceptors, a reduction in muscle spasms and/or a reduction in metabolic enzyme activity levels. [6][7][8] NCV can be altered by gender, age and, more pertinently, skin temperature.9 On this basis it is plausible to propose that cryotherapy could reduce pain via an alteration in NCV. Alternatively, cryotherapy could also be effective as a counterirritant to pain via diffused noxious inhibitory controls, pain gate theory, suppressed nociceptive receptor sensitivity or via the analgesic descending pathway of the central nervous system such as endorphins.1 5 10 11 Evaluation of a counterirritant role is difficult to directly evaluate, but if cryotherapy can reduce pain threshold (PTH) and pain tolerance (PTO) independent of any effect on NCV then these processes may be more important.The aim of the current study, therefore, was to assess changes in NCV, PTH and PTO concomitantly as ankle skin temperature was reduced via cryotherapy. We hypothesise that cryotherapy reduces skin temperature to a level that decreases NCV, and that changes in NCV, are associated with an increase in PTH and PTO.
METHODS
SubjectsA convenience sample of 23 volunteers from local sports clubs were informed individually about the purpose, n...