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The Stretching Window Part Two: Rate of Thermal Decay in Deep Muscle Following 1-MHz Ultrasound

  • Shannon Rose
  • David O. Draper
  • Shane S. Schulthies
  • Earlene Durrant
Publication Date
Jan 01, 1996


Thermal ultrasound can be effective in increasing extensibility of collagen, thus aiding joint mobilization and stretching. In 1995, we reported on the rate of temperature decay following 3-MHz ultrasound in subcutaneous tissues. We repeated that study at 1-MHz frequency to see if the stretching window is different for deep muscle. Twenty subjects had two 23-gauge thermistors inserted 2.5 cm and 5 cm deep into their triceps surae muscle. We administered 1-MHz continuous ultrasound at 1.5 W/cm2 until the tissue temperature increased 4°C (vigorous heating). Immediately following the treatment, we recorded the rate at which the temperature dropped at 30second intervals. We ran a stepwise nonlinear regression analysis to predict temperature decay as a function of time following ultrasound treatment. There was a significant nonlinear relationship between time and temperature decay. At 2.5 cm, the average time for the temperature to drop each degree was: 1°C = 2:34; 2°C = 6:35; 3°C = 12:10: and 4°C = 21:14. At 5 cm, the average time for the temperature to drop each degree was: 1°C = 2:31, 2°C = 6:50: 3°C = 14:32; and 4°C = 27:49. Based upon prior research, thermal decay of 1-MHz ultrasound was slower than 3 MHz, and the deeper tissue cooled at a slower rate than superficial tissue following 1-MHz ultrasound. The data illustrated that the stretching window was open longer for deep-seated structures than for superficial ones.

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