Therapeutic ultrasound (TUS) is clinically used as a deep heating modality for muscle repair enhancement. However, considering the resonance hypothesis, several biophysical effects could be generated in the tissue according the energy output and the TUS mode. PURPOSE: To examine the intramuscular temperature response in exercised muscle, during TUS, delivered in continuous (CON) and pulsed (PUL) mode. METHODS: 8 physically active men (20 ± 0.9y/o; BMI 21.6 ± 1), performed 200 maximal lengthening contractions of the dominant quadriceps in the isokinetic dynamometer. Subjects were randomly assigned to either one of the groups and received treatment 24 h post-exercise. TUS was applied over the vastus medialis in a standardized area of 40cm2, during 8 min, at 1 MHz. For CON, the SATA was 0,5 W/cm2; PUL, SATA 1,5 W/cm2; in both cases the total energy output was 60 J; for placebo (PLA), no energy was delivered. Intramuscular temperature was recorded immediately before treatment and every 30s during the treatment. Isometric peak-torque was determined immediately before exercise and treatment. The study was approved by the local IRB. Comparisons among and between groups were performed by Kruskal-Wallis and Friedman tests, respectively. Linear regression was run to estimate the effect of TUS. RESULTS: Isometric peak torque decreased 24 h but did no exhibit change (109.2 ± 15.6 Nm vs. 102.3 ± 21.3 Nm; p = 0.5). During treatment, the highest temperature recorded was 36.5 ± 0.4 °C for CON; 36.1 ± 0.3 °C for PUL; and 35.9 ± 0.9 °C for PLA. No differences within or among groups were detected after the treatments (CON: -0.05 ± 0.6 °C, p = 0.6; PUL: -0.1 ± 0.1 °C, p = 0.22; PLA: -0.05 ± 0.07 °C, p = 0.15), therefore the rate of temperature change was not determined. Comparisons between baseline and the first 30s evidenced a change in 0.1[[Unsupported Character - Symbol Font °]]C by ultrasound delivered, influenced by the active group (p = 0.03). The remaining measures were not affected by group and showed no linear relationship to temperature. CONCLUSION: No change in temperature in exercised muscle, during TUS treatment at a dosage of 60 J was detected, despite de TUS mode applied. Further studies are necessary to establish tissue energy absorption and dose-response.Supported by the Universidad Industrial de Santander.