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both the acceleration and the deceleration times were increased. Doudet et al. [24,
23] and Benazzouz et al. [2] reported a 25-30% increase in movement duration
in monkeys treated with MPTP compared to normal monkeys. Watts and Mandir
[50] showed that both MPTP-treated animals and Parkinson's disease patients take
longer time to complete the required movements.
11.5.9 Reduction of Peak Velocity
In the experimental study described earlier, one of Godaux et al. [34] findings was
a profound decrease in the peak velocity of movement of PD patients. Camarata et
al. [13] reported that in the MPTP-treated animals, the velocity profiles appeared
less smooth and the amplitude of the velocity profile decreased and delayed in time
at most distances and directions tested. Weiss et al. [52] observed a similar decrease
in the peak velocity of movement of PD patients. Further, Benazzouz et al. [2] and
Doudet et al. [24, 23] after treating monkeys with MPTP found a significant de-
crease in the amplitude of their velocity profiles. Rand et al. [45] reported a signif-
icant reduction of the peak velocity in both accuracy and no-accuracy movement
conditions.
11.5.10 Reduction of Peak Force and Rate of Force Production
Stelmach et al. [48] examined the preparation and the production of isometric force
in Parkinson's disease. PD patients, elderly, and young subjects were asked to gen-
erate a percentage of their maximum force levels. PD patients showed a similar
progression of force variability and dispersion of peak forces to that of control sub-
jects. Force production impairments were seen at the within-trial level. PD patients
were substantially slower in initiating a force production and their peak forces were
reduced.
11.5.11 Movement Variability
Camarata et al. [13] trained monkeys to make two-joint movements on a horizontal
plane by moving a manipulandum in six different directions (30, 90, 150, 210, 270,
and 330) at five distances from a central start box. Velocity and acceleration pro-
files were calculated for both pre- and post-MPTP states. They reported a marked
variability in the onset, peak velocity, and time course of the velocity profile of
MPTP-treated monkeys. Similarly, Stelmach et al. [48] reported variability in the
force profile of Parkinson's disease patients.
