Braking impulse and muscle activation during unplanned gait termination in human subjects with parkinsonism.

Persons with parkinsonism (PD) are known to have difficulty with both rapid force production and declination, and may not be able to adjust force levels during bimanual tasks in the upper extremity. We proposed that these deficits might underlie the problems experienced by those with PD when attempting to rapidly terminate locomotor activity. Rapid gait termination requires concomitant increases in braking impulse and decreases in propulsion impulse. We hypothesized that those with PD would be less able to modulate muscle activity and the associated braking impulse during gait termination. Muscular activity of soleus, tibialis anterior and gluteus medius, and braking impulse were compared between a group of subjects with PD and age and gender matched control subjects. Subjects with PD had similar patterns of muscular activation to control subjects although at dramatically reduced levels of amplitude. Consequently, PD subjects were unable to generate sufficient net braking impulse under time-critical conditions.