Noninvasive analysis of fascicle curvature and mechanical hardness in calf muscle during contraction and relaxation

The purpose of this study was to investigate whether changes of fascicle curvature and muscle hardness of the gastrocnemius muscle during relaxation and isometric contraction could be measured using a noninvasive approach. Seventeen male college students (age 21.0 ± 1.5 years) participated in this study. Measurements were made during the resting state and maximal isometric plantarflexion. Fascicle curvature (m^-1) of the gastrocnemius medialis was measured by ultrasonography. Muscle hardness (kg/mm) was measured with a myotonometer. Angle of ankle joint (°), amplitude of electromyographic activities (mV), and plantarflexion force (kg) were simultaneously recorded using an electrogoniometer, surface electromyography (EMG), and a load cell, respectively. Results demonstrated that the joint angle, electromyographic activities, and force at muscle contraction for the myotonometer and ultrasound conditions were not significantly different (all p > 0.05). Hardness and fascicle curvature during maximal isometric plantarflexion were significantly greater than those at rest (p = 0.002 and p < 0.001, respectively). Correlations between changes in fascicle curvature and changes of muscle hardness that took place between muscle relaxation and maximal contraction were significant (r = 0.832, p = 0.011). This study demonstrates that ultrasonographic and myotonometric measurements are useful to quantify changes in muscle geometry and mechanical properties for muscles during isometric contraction.