Recordings using an isokinetic dynamometer make it possible to quantify the resisting force during passive muscle stretch for a constant speed movement in dorsal flexion (flexion) and its release in plantar flexion (extension). The surface electromyography (EMG) makes it possible to measure voluntary contraction and the movement is considered passive if the corrected and normalized EMG signal, using root-mean-square (RMS), is less than 10% RMS during the Maximal Voluntary Muscle Contraction (MVMC).~Stiffness is calculated from the slope of the rise of the curve during the passive dorsiflexion phase of the joint. The elastic potential energy can be measured and corresponds to the area under the curve during elongation.~During the plantar flexion return phase, there is a hysteresis phenomenon resulting in behavior that differs from the curve. This difference between the two curves corresponds to the behavior related to viscoelastic relaxation. Viscoelasticity has a thixotropic behavior, i.e. it varies over time, for example, with heating. These parameters have been studied together or separately to evaluate the effect of age or stretching on the passive mechanical properties of the calf.~However, the test-retest reliability of the viscoelastic passive properties of the calf muscles assessed using isokinetic device has not been demonstrated.~The investigators designed this study to determine the test-retest reliability of the viscoelastic passive properties of the calf muscles assessed using isokinetic device in flexed and extended knee position. The second objective is to determine the clinical viability of the parameters using the coefficient of repeatability and to investigate the individual characteristics associated with increased calf stiffness or altered viscoelasticity~Muscle tension is expressed by the peak torque (Nm), recorded at neutral position (PT0°) and 10° flexion (PT10°). Plantarflexor stiffness is determined as the slope of the torque-angle curve expressed as Nm·degree-1 during the linear region form 0-10° flexion (Slope0-10). A measure of elastic energy storage is calculated through the AUC of the torque-angle curve across the all range of motion. Hystérésis over time due to viscoelastic stress relaxation is calculated as the percent reduction in work absorption between the muscle stretching and releasing phases . The flexed-to-extended ratio is calculated as the ratio of flexed knee to extended knee and evaluated for PT0°, PT10° and Slope0-10 values , at 5 and 90°/sec
The investigators designed this study to determine the test-retest reliability of the viscoelastic passive properties of the calf muscles assessed using isokinetic device in flexed and extended knee position. The second objective is to determine the clinical viability of the parameters using the coefficient of repeatability and to investigate the individual characteristics associated with increased calf stiffness or altered viscoelasticity