Objective
To observe changes in reflex threshold and gain in spastic muscles and to find useful parameters in biomechanical assessment of spasticity.

Method
Ankle plantar flexor muscles of twenty two hemiplegic patients were stretched by isokinetic dynamometer. Stretching was done at the velocities of 10^o/sec, 300^o/sec, and at the threshold velocity (e.g. lowest velocity at which electromyographic evidence of stretch reflex was recorded). Peak eccentric torque, torque at joint angle of 20^o, torque threshold angle, and stiffness index were measured.

Results
Peak eccentric torque and stiffness index were increased and torque threshold angle was decreased in hemiplegic side. Peak eccentric torque and stiffness index were increased at 300^o/sec compared to 10^o/sec. Stiffness index showed significant correlation with modified Ashworth scale at 300^o/sec and threshold velocity.

Conclusion
Both reflex threshold and reflex gain were changed in spastic muscles. Stiffness index was thought to be one of useful parameters in biomechanical assessment of spasticity.