Chronic effects of muscle and nerve-directed stretching on tissue mechanics

Abstract

Tissue-directed stretching interventions can preferentially load muscular or non-muscular structures such as peripheral nerves. How these tissues adapt mechanically to long-term stretching is poorly understood. This randomized, single-blind, controlled study used ultrasonography and dynamometry to compare the effects of 12-week nerve-directed and muscle-directed stretching programs versus control on: maximal ankle dorsiflexion range of motion (ROM) and passive torque, shear wave velocity (SWV; an index of stiffness) and architecture of triceps surae and sciatic nerve. Sixty healthy adults were randomized to receive nerve-directed, muscle-directed stretching, or no intervention (control). The muscle-directed protocol was designed to primarily stretch the plantar flexor muscle group, while the nerve-directed intervention targeted the sciatic nerve tract. Compared with the control group (mean; 95% Confidence Interval), muscle-directed intervention showed increased ROM (+7.3°; 95% CI: 4.1-10.5), decreased SWV of triceps surae (varied from -0.8 to -2.3m/s across muscles), decreased passive torque (-6.8N.m; 95% CI: -11.9 to -1.7), and greater gastrocnemius medialis fascicle length (+0.4cm; 95% CI: 0.1 to 0.8). Muscle-directed intervention did not affect the SWV and size of sciatic nerve. Participants in nerve-directed group showed a significant increase in ROM (+9.9°; 95% CI: 6.2 to 13.6) and a significant decrease in sciatic nerve SWV (> -1.8m/s across nerve regions) compared with the control group. Nerve-directed intervention had no effect on the main outcomes at muscle and joint levels. These findings provide new insights into the long-term mechanical effects of stretching interventions, and have relevance to clinical conditions where change in mechanical properties has occurred.

Effects of Static Stretching With High-Intensity and Short-Duration or Low-Intensity and Long-Duration on Range of Motion and Muscle Stiffness

“…Thus, we suggested that stretching intensity was important to decrease muscle stiffness than stretching duration. Recently, the previous studies indicated that the dorsiflexion ROM could be increased immediately and chronically increased after stretching intervention because of the change in sciatic nerve stiffness not muscle stiffness (Andrade et al, 2018(Andrade et al, , 2020. However, in this study, the change in sciatic nerve stiffness was not measured.…”

The effects of 12 weeks of static stretch training on the functional, mechanical, and architectural characteristics of the triceps surae muscle–tendon complex

“…The discrepancy can be attributable to different training modality, such as intensity, frequency, number of exercises, and overall duration (Freitas et al 2018 ). Concerning GM muscle stiffness, another possible explanation could be that PST affected differently the stiffness of the individual triceps surae muscles and/or the regional stiffness within each muscle, as observed by shear-wave ultrasound imaging technique (Andrade et al 2020 ). Nonetheless, it seems that combining several weeks of training with high weekly exercise frequency, as it has been done in the present study, can lead to MTC and GM muscle stiffness adaptations.…”

“…Since previous studies showed that the different triceps surae muscles can undergo different strain during stretch exercise (Hirata et al 2016 ) and within the same muscle different portions can be unequally affected by the stretch manoeuvre (Andrade et al 2020 ), we examined the possible PST-induced architectural adaptations in all triceps surae heads at different regions.…”

“…The PST programme consisted of 12 weeks of training, 5 sessions per week (60 sessions in total). This choice was based on recent studies pointing out that investigations providing the participants with an adequate training volume (i.e., weekly frequency > 3 times/week, total duration > 8 weeks) were needed to clarify the effects of PST on the functional, mechanical and architectural characteristics of the MTC (Freitas et al 2018 ; Nakamura et al 2020 ; Andrade et al 2020 ). Each session included two manoeuvres for plantarflexor muscles (Fig.…”

“…As final consideration, in light of previous studies (Simpson et al 2017;Andrade et al 2020), it can be speculated that combining overloaded stretching training with high training volume could lead to possible structural adaptations in the stretched muscles at rest. Future studies are needed to explore this hypothesis.…”