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face electrodes as the subjects were performing the task. Godaux et al. [34] found
that the amplitudes of the peak EMG activity were reduced and the rates of de-
velopment of muscle activity in both flexors and extensors were depressed in PD
patients.
Corcos et al. [17] measured the maximum elbow flexor and extensor muscle
strength in patients with PD during on and off anti-PD medication. Patients were
tested in two maximally produced muscle isometric contractions and two flexion
contractions equal to 50% of their maximal voluntary contractions. In all four con-
ditions, the patients were seated on a table with fully supinated right forearm flexed
90
◦
with respect to the arm and positioned vertically. The forearm was attached to a
stiff steel bar and changes in torque were measured by strain gauges. EMG signals
were recorded with surface electrodes. Corcos and colleagues reported a reduction
in the peak torque and in the rate of change of torque.
Watts and Mandir [50] trained PD patients and age-matched controls to perform a
rapid, wrist flexion task. Their hands were hidden from their view. Visual cues were
used to instruct the subjects where and when to move. The subjects were advised to
move as quickly and as accurately as possible once they were given the go-signal.
Their flexor and extensor electromyographic (EMG) activities were recorded us-
ing surface electrodes during the trials. They noted decreased average amplitude of
EMG activity for the patients with Parkinson's disease. Doudet et al. [24, 23] re-
ported that the rate of development and peak amplitude of the first agonist burst
of EMG activity were depressed. Similarly, Hallett and Khoshbin [37] observed, in
patients with Parkinson's disease, there was a similar reduction in the activity of the
first agonist burst as if it has reached a ceiling.
11.5.8 Movement Time Is Significantly Increased
Rand et al. [45] trained PD patients and age-matched controls to make rapid arm
movements with or without accuracy constraints. Subjects were seated in front of a
horizontal digitizer and held a stylus. The subject was required to move the stylus
from a home position to a target position after an auditory signal. In the spatial
accuracy condition, the subjects were required to move the stylus to the defined
target and stop on it, whereas in the
n
-spatial accuracy condition, the subjects were
asked to move toward the target without stopping precisely on it. The subjects were
asked to make their movements as fast and as accurate as possible. Rand et al. [45]
reported that the movements of patients were slower than those of the controls in
both the acceleration phase and the deceleration phase. The prolonged deceleration
phase for the patients was more pronounced in the target condition. In addition,
the kinematics of PD patients were abnormal, characterized by a higher number
of acceleration zero crossings indicating that their movements were segmented and
that the first zero crossing occurred much earlier in the movement. Weiss et al.
[52] trained and tested young, elderly, and PD subjects in making discrete elbow
movements with varying amplitudes to targets of varying sizes. They reported that
