Comparison of Muscle Temperature Increases Produced by Moist Hot Pack and ThermoStim Probe

ThermoStim Probe (TSP) has recently joined the market as a superficial heating modality. Although there is limited research into the intramuscular heating capability of superficial heating modalities in general (moist hot pack [MHP], paraffin, warm whirlpool), no previous research has examined intramuscular heating capability of TSP. Evaluate rate and magnitude of intramuscular heating via TSP compared with hydrocollator MHP, and determine if TSP can increase tissue temperature 3°C-4°C (vigorous heating range). Repeated-measures counterbalanced study. Multisite trial; 2 college/university research laboratories. A total of 18 healthy college-aged participants (11 females and 7 males, age: 23.0 [2.1] y, weight: 74.64 [18.64] kg, height: 168.42 [9.66] cm, subcutaneous adipose: 0.71 [0.17] cm) with calf subcutaneous adipose <1.2 cm. MHP and TSP were applied to the posterior aspect of the nondominant calf for 20 minutes; participants underwent each treatment in a counterbalanced order. Muscle temperature at a depth of 1.5 cm was measured via 21-gauge catheter thermocouple. Temperatures were recorded at baseline and during the 20-minute treatment. There was a significant treatment-by-time interaction during the treatment period (F_5,85 = 14.149, P < .001), as well as significant main effects for treatment (F_1,17 = 7.264, P = .02) and for time (F_5,85 = 34.028, P < .001). Muscle temperature increased an average of 1.7° (0.9°) for the MHP and 0.6° (1.0°) for the TSP. Pairwise comparisons of the interaction (using least significant difference adjustment for multiple comparisons) indicated that MHP heated faster than TSP at minutes 12 (P = .02), 16 (P = .002), and 20 (P = .001). There was no significant correlation between subcutaneous adipose thickness and maximum temperature increase obtained with either MHP (r = -.033, P = .90) or TSP (r = -.080, P = .75). MHP increased intramuscular temperature significantly more than TSP; however, neither modality was capable of producing a 3°C-4°C temperature increase associated with increased tissue extensibility.