We stretched quadriceps femoris in healthy subjects and in patients wi
th a recent diagnosis of PD in order to assess whether modifications o
f the long-latency component of the stretch reflex is an early event i
n the course of Parkinson's disease (PD). We found a modified mechanic
al and electromyographic (EMG) behavior in stretching relaxed muscles
of patients while voluntary activation greatly reduced differences bet
ween normal and Parkinsonian subjects, suggesting that a lower thresho
ld of the response is an early sign in PD.