Quantification of tendon reflex in normal and spastic limbs

Tendon reflexes of the knee and elbow extensor muscles were studied for thirteen normal subjects and twenty spinal cord injured and stroke patients with mild to severe spasticity. A hand-held instrumented hammer was used to tap the patellar and triceps muscle tendons and measure the tapping force, while the quadriceps/triceps muscle EMG signals and knee/elbow joint extension torques were measured as the reflex responses. Tendon reflex gain (TRG) was quantified as the gain from the tapping force to reflex torque. It was found that the TRG as a function of joint flexion angle had an ascending-descending shape. Statistical test showed that the TRG of both spastic knees and spastic elbows was significantly higher than that of their normal counterparts at the significance level of 1%.