Objective
We designed this study to evaluate muscle tone by using a biomechanical method and to provide data for the future studies about muscle tone.

Method
We evaluated 29 subjects without known neuromuscalar diseases using the biomechanical method. Both plantar flexors of each subject were passively stretched by isokinetic dynamometer from 30^oplantar flexion position to 10^odorsiflexion position. Peak eccentric torque (PET) and torque threshold angle (TTA) were calculated at angular velocity of 10^o/sec, 90^o/sec and 300^o/sec. Regression lines from torque/position curve at 10^o/sec and 300^o/sec were considered an intrinsic stiffness index (ISI) and total stiffness index (TSI). Stretch reflex threshold speed (SRTS) was defined as the minimum speed of plantar flexion movement in which EMG reflex activity in plantar flexor muscles is induced.

Results
The mean of TTA was higher in 10^o/sec than in 300^o/sec. The means of ISI and TSI were 0.11⁑0.08, and 0.18⁑0.04. The mean of SRTS was 125.2⁑48.3^o. No statistical difference in each parameter was found according to the side or gender.

Conclusion
ISI, TSI, PET, TTA and SRTS using a biomechanical method are thought to be useful parameters for the quantitative assessment of muscle tone change of ankle plantar flexors.