Preservation of directly stimulated muscle strength in hemiplegia due to stroke

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.