Author(s): SAKURADA, R., UMEDA, T., SUGIYAMA, K., HIRASAWA, H., HOJO, T., Institution: DOSHISHA UNIVERSITY, Country: JAPAN, Abstract-ID: 842

INTRODUCTION:
In sports, muscle injuries frequently occur at the medial gastrocnemius (MG) (Koulouris, 2007). Previous research has shown that a higher risk of muscle injury is associated with higher muscle stiffness (Watsford, 2010). To decrease muscle stiffness, massage and superficial thermal stimulation are commonly used in clinical practice (Eriksson, 2014). However, injuries of MG have not been prevented yet. In the present study, we focused on ultrasound (US) stimulation, which has mechanical vibration and heating effects on the deep tissues (Cameron, 2015). Heating effects of US stimulation may have the possibility of decreasing the stiffness of deep muscles, but it has not been adequately investigated yet. Thus, this study aimed to assess the effects of US stimulation on muscle stiffness of the MG.
METHODS:
Ten healthy men (21.8±2.1yo) were recruited for this study. US stimulation (1 MHz, 2.0 W/cm², PYSIO SONO, SAKAI medical) was applied for 10 minutes to the skin over the MG of one leg in the prone position, while the contralateral leg served as the control. The shear wave velocity (SWV) of the MG, which is an index of muscle stiffness, was measured with the shear wave elastography mode of an ultrasound device (LOGIQ P10, GE Healthcare). SWV was assessed at 3 time points: before, just after and 10 minutes after the stimulation. Two-way ANOVA (2 legs x 3 time points) was performed for statistical analysis.
RESULTS:
The SWV of the MG just after US stimulation was significantly lower than that before stimulation (p = 0.016) and that of the control leg (p < 0.001). The SWV 10 minutes after the stimulation was higher than that just after the stimulation, but significant correlations were not observed (p=0.104). No significant correlations were found between the SWV before stimulation and that 10 minutes after stimulation (p=1.000).
CONCLUSION:
An increase in tissue temperature decreased the stiffness of the tissue (Huang, 2009). It has been shown that applying 1 MHz x 10 minutes US stimulation increased the temperature of medial aspect of the triceps surae muscle 2.5 cm beneath the skin by 4.0°C (Draper, 1995). In this study, we proved that applying US stimulation decreased the stiffness of the MG. Thus, the heating effect of US stimulation may decrease muscle stiffness. However, this study also showed that the thermal effect of US stimulation did not persist for 10 minutes after adaptation. Raccuglia (2016) has reported that passive muscle heating following warm-up reduced the drop in muscle temperature by approximately 25 % over 30 min. Therefore, using US stimulation after warm-up may help sustain elevated muscle temperature and may contribute to injury prevention effectively.