Tibial nerve stiffness is related to maximum angle of ankle dorsiflexion

Maximum angle of ankle dorsiflexion is affected by the triceps surae muscle stiffness and stretch tolerance, which may be reflected by the tibial nerve stiffness. However, no study has evaluated the triceps surae muscle and tibial nerve stiffnesses simultaneously or clarified their correlation with the maximum angle. This study aimed to investigate the correlation between the maximum angle and both the stiffnesses. Forty-one healthy adults participated. The maximum angle of ankle dorsiflexion and shear wave velocities of the triceps surae muscles and tibial nerve at 5°, 15°, and 25° ankle dorsiflexion were measured. Multiple linear regression analysis was performed using forced entry method, specifying the shear wave velocities of the four tissues as the independent variables and the maximum angle as the dependent variable. This analysis was performed at each angle where the shear wave velocity was measured. Multiple linear regression analysis was also performed using stepwise method, specifying the shear wave velocities of the tibial nerve at the three angles as the independent variables and the maximum angle as the dependent variable. Using the forced entry method, the shear wave velocity of the tibial nerve at each angle was significantly negatively correlated with the maximum angle, whereas those of the muscles were not. Using the stepwise method, only the shear wave velocity of the tibial nerve at 25° was significantly negatively correlated with the maximum angle. These results suggest that the tibial nerve stiffness at a higher length seems to be one determinant of the maximum angle.