Continuous vs. pulse ultrasound therapy on the flexibility of short hamstring muscles

Background: Ultrasound has been a widely used and well-accepted physical therapy modality for the management of musculoskeletal conditions. However, there is a lack of scientific evidence on its effectiveness. We studied the effect of two different modes of ultrasound (continuous vs pulse) in reducing the shortening of hamstrings. Methods: Thirty non-impaired men aged 20 to 30 years (mean 23.84 years) were included in this study. They were randomly divided into two groups. Group 1 was composed of 15 subjects who underwent 10 sessions of continuous ultrasound (2 W/cm², 1 MHz, 5 min) and group 2 was composed of 15 subjects who underwent 10 sessions of pulsed ultrasound (200 microsecond burst of 1 MHz sine waves repeated at 1 KHz, 0.5 W/cm², 5 min). Ultrasound applied over their short hamstrings. Hamstring flexibility was evaluated by passive knee extension test at the base line and following interventions. Results: Both methods of treatment were capable of significantly improving the flexibility of hamstring muscles (P < 0.01). The hamstring flexibility were significantly improved in the continuous ultrasound group compared to pulsed ultrasound group (P < 0.001). Conclusion: It seems that heating effects of continuous ultrasound may be more effective than non-thermal properties of pulsed ultrasound for increasing the flexibility of shorted hamstring.