Objective: To investigate the analgesic effort of local superficial heating by studying sympathetic skin responses.
Design: Randomized trial.
Setting: Electromyography laboratory in the department of physical therapy and rehabilitation of a university hospital.
Subjects: Twenty healthy volunteers participated with informed consent.
Interventions: Sympathetic skin response (SSR) amplitudes following electrical stimulation of the right peroneal nerve and skin temperatures in both hands were recorded simultaneously. All of the recordings were repeated at 5-minute intervals during local heat application over the right palm and within 15 minutes after heat application was stopped.
Results: SSR amplitudes in both hands decreased significantly during local heating (p < .05) and did not return to their initial levels within 15 minutes of the recovery period; the reductions remained statistically significant (p < .05). Amplitude reductions were statistically more significant on the heated hand compared with those on the contralateral hand (p < .05).
Conclusion: Therapeutic local heat application reduces the sudomotor response to a painful stimulus. This analgesic effect may be due to suppression of cortical pain sensation resulting from increased levels of endorphins, and may also be a result of local inhibition of both afferent and efferent C fibres.