Purpose: Instrument-assisted soft tissue mobilization (IASTM) has been reported to improve joint range of motion (flexibility). However, it is not clear whether this change in the joint range of motion is accompanied by any alterations in the mechanical and/or neural properties. This study aimed to investigate the effects of IASTM in plantarflexors and Achilles tendon on the mechanical and neural properties of them. Methods: This randomized, controlled, crossover study included 14 healthy volunteers (11 men and 3 women, 21–32 yr). IASTM was performed on the skin over the posterior part of the lower leg for 5 min and targeted the soft tissues (gastrocnemii, soleus, and tibialis posterior muscles; overlying deep fascia; and Achilles tendon). As a control condition, the same participants rested for 5 min between pre- and postmeasurements without IASTM on a separate day. The maximal ankle joint dorsiflexion angle (dorsiflexion range of motion), the peak passive torque (stretch tolerance), and the ankle joint stiffness (slope of the relationship between passive torque and ankle joint angle) during the measurement of the dorsiflexion range of motion and muscle stiffness of the triceps surae (using shear wave elastography) were measured before and immediately after the interventions. Results: After IASTM, the dorsiflexion range of motion significantly increased by 10.7% ± 10.8% and ankle joint stiffness significantly decreased by −6.2% ± 10.1%. However, peak passive torque and muscle stiffness did not change. All variables remained unchanged in the repeated measurements of controls. Conclusion: IASTM can improve joint range of motion, without affecting the mechanical and neural properties of the treated muscles.

A novel stretching modality was developed to provide repetitive small length changes to the plantar flexors undergoing passive stretch defined as "minute oscillation stretching" (MOS). This study investigated the effects of MOS on neuromuscular activity during force production, the rate of torque development (RTD), and the elastic properties of the plantar flexors and Achilles tendon. Ten healthy males participated in this study. The neuromuscular activity of the triceps surae and tibialis anterior muscles during maximal voluntary plantar flexion torque [MVT], RTD of plantar flexion, Achilles tendon stiffness, and muscle stiffness were measured before and after two types of interventions for a total of 5 minutes: static stretching (SS) and MOS at 15 Hz and without intervention (control). Achilles tendon stiffness was calculated from the tendon elongation measuring by ultrasonography. Muscle stiffness was determined for the medial gastrocnemius [MG] using shear wave elastography. The MVT, mean electromyographic amplitudes [mEMG] of MG and lateral gastrocnemius [LG], and RTD were significantly decreased following SS (MVT: −7.2 ± 7.9%; mEMG of MG: −8.7 ± 10.2%; mEMG of LG: −12.4 ± 10.5%; RTD: −6.6 ± 6.8%), but not after MOS. Achilles tendon stiffness significantly decreased after SS (−13.4 ± 12.3%) and MOS (−9.7 ± 11.5%), with no significant differences between them. Muscle stiffness significantly decreased in SS and MOS, with relative changes being significantly greater for MOS (−7.9 ± 8.3%) than SS (−2.3 ± 2.9%) interventions. All variables remained unchanged in the controls. In conclusion, MOS changed muscle‐tendon compliance without loss of muscle function.

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.

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.

Static stretching increases flexibility but can decrease muscle strength, and the method to avoid the latter has been longed for. In this study, a novel stretching modality was developed that provides repetitive small length changes to the plantar flexor muscles undergoing passive static stretching (“local vibration stretching,”). We investigated the effects of local vibration stretching on muscle strength, flexibility and its persistence. Plantar flexion strength and maximal ankle joint dorsiflexion angle (dorsiflexion range of motion) were measured for 10 healthy young males before (pre) and immediately after (post) three types of stretching: static stretching, local vibration stretching at 15 Hz, and no intervention (control). The dorsiflexion range of motion was measured also at 15, 30, and 60 min post-stretching. Elongation of the medial gastrocnemius and Achilles tendon was determined by ultrasonography. Plantar flexion strength significantly decreased by 4.3 ± 3.5 % in static stretching but not in local vibration stretching. The dorsiflexion range of motion significantly increased both in static stretching (7.2 ± 8.1 %) and local vibration stretching (11.2 ± 14.6 %) which was accompanied by a significantly larger muscle elongation but not tendon elongation. Elevated dorsiflexion range of motion was maintained until 30 min after the local vibration stretching while it returned to baseline level (pre-intervention) in 15 min after the static stretching. All variables remained unchanged in the control condition. In conclusion, local vibration stretching improves extensibility of the muscle belly without decreasing strength, and the increased flexibility is retained longer than static stretching.