Background Hemiplegia, or hemiparesis, severe impairment of purposeful activation
of striated musculature, is the most conspicuous and often most disabling
symptom of acute cerebrovascular lesions. Spontaneous improvement of voluntary
strength may extend over many months.
Objective In this archetypical upper motor neuron syndrome we wish to ascertain
the degree of functional impairment due to direct contractile impairment of
the affected striated musculature.
Design Maximal tetanic muscle contraction was elicited by electrical stimulation
applied directly to the tibialis anterior of the paretic and nonparetic limbs.
Maximal forces of the normal limbs were compared with the afflicted limbs
both early and late after vascular lesions of the pyramidal tract. Maximal
voluntary force of foot dorsiflexion in the same limbs was also determined.
Similar measurements were made in healthy control participants.
Setting Acute hospital, rehabilitation, and outpatient units of a clinical research
center.
Patients Patients with unilateral stroke were studied a few or many weeks after
the ictus.
Main Outcome Measures Comparison was made between contraction strengths induced by maximal
tetanic electrical stimulation of the dysfunctional and contralateral unaffected
muscles. Maximal voluntary strength of the foot dorsiflexion forces was also
measured.
Results Compared with the range of electrically evoked contractile force of
tibialis anterior between the limbs of healthy participants, the directly
elicited force in stroke-impaired tibialis anterior was not significantly
impaired.
Conclusions Modes of exercise therapy focused primarily on direct strengthening
of striated musculature, as in resistive exercise training, are strategically
questionable. Whether other approaches may be more effective remains to be
proved. The central disability of the upper motor neuron syndrome is failure
of rapid coordinated adjustment of graded high-frequency motoneuron firing
in purposeful complex synergies.
