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.