Ultrasound is a form of mechanical energy with its acoustic pressure wave at frequencies range from 20 to 20,000 Hz. To date, ultrasound waves are not only used in imaging medicine for diagnosis, but also are performed in physical therapy (PT) medicine for the purpose of preventing and curing disease due to its thermal and non-thermal effects, and the ultrasound frequencies used in PT are typically between 1.0 and 3.0 MHz. Low-intensity pulsed ultrasound (LIPUS) typically has an intensity at 30 mW/cm, pulse ratio 1:4 at 1,000 Hz, and frequency at 1.5 MHz, which has been demonstrated to have lots of beneficial effects in promoting bone-fracture healing, accelerating soft-tissue healing, inhibiting inflammatory responses and so on. The underlying mechanisms of biological effects of therapeutic ultrasound in PT medicine may be associated with the upregulation of cell proliferation through activation of integrin receptors and Rho/ROCK/Src/ERK signaling pathway, and with promoting multilineage differentiation of mesenchyme stem/progenitor cell lines through ROCK-Cot/Tpl2-MEK-ERK signaling pathway. However, it still needs an intense effort for basic-science and clinical investigators to explore the cellular and molecular mechanisms and biomedical applications of LIPUS on human body in the future.
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