Study Design: A repeated measure cross-over design was used. The indepentent variable was the type of ultrasound (pulsed or continuous) and the dependent variable was intramuscular temperature. Objective: To compare changes in intramuscular temperature of pulsed ultrasound against continuous ultrasound with an equivalent spatial average temporal average (SATA) intensity. Background: There is a lack of research on the heat generating capabilities of pulsed ultrasound within human muscle. Methods and Measures: Subjects were 16 volunteers free of left lower extremity injury. Each subject was treated with pulsed ultrasound and continuous ultrasound during a single testing session. Tissue temperature returned to baseline and stabilized between treatments and treatment order was randomized. Tissue temperature was measured every 30 seconds using a 26-gauge needle microprobe inserted at a depth of 2 cm in the left medial gastrocnemius muscle. Data were analyzed using a linear mixed model. Results: Treatment with continuous ultrasound produced a mean temperature increase of 2.8, 0.8C above baseline. Treatment with pulsed ultrasound produced a mean temperature increase of 2.8, 0.7C above baseline. Statistical analysis revealed no significant differences in either the extent or rate of temperature increases between the two modes of ultrasound application. Conclusion: Pulsed ultrasound produces similar intramuscular temperature increases as continuous ultrasound at a 2 cm depth in the human gastrocnemius. Spatial average temporal average intensity is an important consideration when selecting pulsed ultrasound parameters intended to deliver “non-thermal” effects.
