The Regulatory Effects of Low-Intensity Pulsed Ultrasound Combined With Stretching on Muscle Tension Relief: Focusing on the Microstructural Mechanism.

While often associated with neurological conditions, muscle dysfunction may also result from primary myopathies and other non-neurological causes, contributing significantly to motor impairment and reduced quality of life. Conventional therapeutic approaches, including electrotherapy, cryotherapy and pharmacological interventions, exhibit limited efficacy and potential adverse effects. By comparison, low-intensity pulsed ultrasound (LIPUS) has emerged as a promising research focus due to its non-invasive nature, safety profile and therapeutic efficiency. This study presents a novel approach for muscle regulation through the synergistic modulation of ultrasonic stimulation and mechanical stretching. Through integrated imaging analysis and histological examination techniques, we systematically evaluated its modulatory effects on muscular microstructure. A constant pre-strain was applied to simulate muscle stretching conditions, with concurrent LIPUS interventions at intensities of 50, 100 and 150 mW/cm². The study analyzed muscle texture characteristics by acquiring B-mode ultrasound images. Enzyme-linked immunosorbent assay, quantitative real-time polymerase chain reaction and hematoxylin-eosin staining were employed to examine LIPUS-induced regulatory effects on the extracellular matrix and evaluate changes in muscle fiber spacing. The research has found that ultrasound plays a dominant role. Compared to initial measurements, entropy, standard deviation and contrast were significantly reduced, while angular second moment, inverse difference moment and mean values showed marked increases. In the 100 and 150 mW/cm² groups, ultrasound stimulation led to an expansion of muscle fiber spacing, whereas no significant effect was observed in the 50 mW/cm² group. In conclusion, this study confirms that LIPUS enhances the therapeutic efficacy of stretching through promoting muscle fiber realignment.