Effect of coupling medium temperature on rate of intramuscular temperature rise using continuous ultrasound

We determined the effects of coupling medium temperature on the rate of intramuscular temperature rise (RTR) during continuous ultrasound.

Ultrasound was applied in a continuous mode at a frequency of 1 MHz and intensity of 1.5 W/cm(2). Each subject received 3 treatments, using water-based coupling gel at temperatures of 18 degrees C, 25 degrees C, and 39 degrees C. All treatments were performed in an athletic training room under controlled environmental conditions.

Eighteen healthy male subjects (mean age = 23.6 +/- 3.5 years; height = 177.8 +/- 6.9 cm; weight = 76.6 +/- 8.2 kg; calf size = 37.6 +/- 2.4 cm) participated in this study.

A thermistor was inserted into the left medial triceps surae at a depth of 5 cm, and baseline tissue temperatures were recorded before treatment. Intramuscular temperature was recorded every 30 seconds until the temperature rose 4 degrees C above baseline or until discomfort was felt. RTR was calculated by dividing the absolute temperature change by treatment time.

A 1-way, repeated-measures analysis of variance revealed a significant difference in RTR among gel temperatures, RTR was significantly faster using the 25 degrees C gel compared with the 18 degrees C and 39 degrees C gels. There was no difference between the 18 degrees C and 39 degrees C gel treatments.

These results suggest that the use of a cooled or heated gel may be counterproductive when maximal thermal effects are desired within a given time frame.