Acute effects of static stretching on skeletal muscle relaxation at different ankle joint angles

Purpose: By combining electromyographic (EMG), mechanomyographic (MMG) and force analysis, the electromechanical delay during muscle relaxation (R-DelayTOT) was partitioned into electrochemical and mechanical components. The study aimed to evaluate the effects of changes in joint angle on R-DelayTOT components during relaxation after electrically evoked contractions before and after static stretching (SS) administration. Methods: Nineteen male participants (age 24 ± 3 years; body mass 76.4 ± 8.9 kg; stature 1.78 ± 0.09 m; mean ± SD) were evaluated. Passive torque (Tpass) of the plantarflexor muscles was measured at 0°, 10°, and 20° of dorsiflexion to determine joint stiffness. The maximum electrically evoked torque (pT) was also recorded at each angle. During pT, force, EMG and MMG signals were detected for offline calculations of R-DelayTOT and its electrochemical and mechanical components. The same procedures were repeated after SS. Results: With increase in dorsiflexion angle, joint stiffness increased while R-DelayTOT and its mainly mechanical components decreased (from −8 to 20 %, P < 0.05). After SS, joint stiffness decreased (from 16 to 20 %, P < 0.05), while R-DelayTOT and its mainly mechanical components lengthened (from 8 to 28.5 %, P < 0.05). Moreover, post-SS R-DelayTOT and its components decreased with the increase in joint angle (from −13 to 31 %, P < 0.05). Conclusion: The reduction in R-DelayTOT with increase in joint angle could be ascribed to the increase in joint stiffness, and not to alterations of the electrochemical processes during relaxation. SS lengthened R-DelayTOT and its components with a concomitant decrease in joint stiffness. Nevertheless, the reduction of the R-DelayTOT mainly mechanical components seen with dorsiflexion was similar to that before SS. © 2016, Springer-Verlag Italia.