Kazuya Hiratsuka

Dynamic stretching (DS) is a conditioning technique commonly used in sports. However, its effects on contralateral joint flexibility and elastic properties of the targeted muscle over several weeks remain unclear. Similarly, its impact on muscle functions, such as force or power exertion, is poorly understood. This study aimed to examine the effects of a 12-week DS program targeting the ankle plantar flexors on the joint flexibility, muscle strength, and elastic properties of the plantar flexors in stretched and contralateral legs. Eighteen healthy young adults (12 males and six females, aged 18-24 years) participated in this study. DS was performed on one leg of the ankle plantar flexors for 12 weeks (3 days weekly), while the other leg served as a non-intervention. Dorsiflexion range of motion (DFROM), muscle stiffness, and ankle plantar flexion strength (rate of torque development and isokinetic muscle strength) were assessed before and after the intervention. The muscle stiffness was measured using shear wave elastography on the gastrocnemius. DFROM significantly increased in both conditions (p < 0.05), whereas gastrocnemius stiffness significantly decreased only in the DS condition (p < 0.05). No significant changes were observed in the non-intervention condition. The ankle plantar flexion rates of torque development and isokinetic strength did not change in either condition. These findings suggest that 12 weeks of DS can reduce muscle stiffness and improve joint flexibility without affecting muscle strength while enhancing contralateral joint flexibility without altering muscle stiffness or strength.

Instrument-assisted soft tissue mobilization (IASTM) stimulates soft subcutaneous tissues by applying pressure to the skin with a specialized bar or spurtle-like instrument. No studies have verified whether several weeks of continuous IASTM alone can alter joint flexibility and musculotendinous properties in healthy participants. We examined the effect of a 6-week IASTM program on joint flexibility and the musculotendinous properties of the lower limbs. Fourteen healthy men (aged 19–35 years) who participated in a 6-week IASTM program (3 days weekly) for the soft tissue of the posterior aspect of one lower leg were included. The other leg served as the control. Before and after the intervention, we measured the maximal ankle joint dorsiflexion angle (dorsiflexion range of motion: DFROM) and maximal passive torque (MPT), a measure of stretch tolerance. We measured muscle and tendon stiffness using shear wave elastography on the gastrocnemius and Achilles tendon. IASTM significantly increased the DFROM and MPT (p < 0.05 for both). However, no significant changes were observed in muscle and tendon stiffness. None of the parameters changed significantly in the control group. The 6-week IASTM program increased stretch tolerance and joint flexibility but did not change muscle and tendon stiffness.