Effects of therapeutic ultrasound on range of motion and stretch pain

[Purpose] This study aimed to clarify the effects of therapeutic ultrasound on range of motion and stretch pain and the relationships between the effects. [Subjects] The subjects were 15 healthy males. [Methods] Subjects performed all three interventions: (1) ultrasound (US group), (2) without powered ultrasound (placebo group), and (3) rest (control group). Ultrasound was applied at 3 MHz with an intensity of 1.0 W/cm(2) and a 100% duty cycle for 10 minutes. The evaluation indices were active and passive range of motion (ROM), stretch pain (visual analog scale; VAS), and skin surface temperature (SST). The experimental protocol lasted a total of 40 minutes; this was comprised of 10 minutes before the intervention, 10 minutes during the intervention (US, placebo, and control), and 20 minutes after the intervention. [Results] ROM and SST were significantly higher in the US group than in the placebo and control groups for the 20 minutes after ultrasound, though there was no change in stretch pain. [Conclusion] The effects of ultrasound on ROM and SST were maintained for 20 minutes after the intervention. The SST increased with ultrasound and decreased afterwards. Additionally, the SST tended to return to baseline levels within 20 minutes after ultrasound exposure. Therefore, these effects were caused by a combination of thermal and mechanical effects of the ultrasound.