Applying thermal therapy: Comparison of different commercially available heating devices to increase muscle temperature.

Although various medical devices are available for the purpose of heat therapy, their effect on muscle temperature remains unclear. This study compared the effects of a water-perfused suit (WPS), short-wave diathermy (SWD) and hot-water immersion (HWI) on muscle, core and skin temperatures, along with perceived thermal discomfort. Ten healthy volunteers (four males and six females) were exposed to WPS, SWD or HWI for 1 h on three occasions, separated by 3-7 days, in a counterbalanced order. Muscle temperature increased with all devices (P < 0.0001, partial η2 = 0.55) but was lower after WPS in comparison to both SWD (P = 0.00656) and HWI (P = 0.00949). Core temperature was higher with HWI than with WPS (P ≤ 0.0104) and SWD (P ≤ 0.0213) from 20 min onwards. Although the average skin temperature over the thigh was lower with SWD than with HWI (P = 0.007, -1.2 [-2.0; -0.4]°C), the maximal local skin temperature was higher with SWD than with HWI (P = 0.0153, -0.7 [-1.4; -0.2]°C). Thermal discomfort was higher during HWI than during WPS (P ≤ 0.0159) and SWD (P ≤ 0.0130). In conclusion, only SWD and HWI increased muscle temperatures. SWD was able to increase local muscle temperatures comfortably, but the effects were localized. HWI can increase both peripheral and central temperatures easily, but the associated increases in core temperature might lead to hyperthermia-induced discomfort.