Clin Neurophysiol. 2010 May 5.

Non-paretic quadriceps activity influences paretic quadriceps activity post-stroke.

Lewek MD, Breslin R, Hlad L, Lanton A, St John J.

Department of Allied Health Sciences, Division of Physical Therapy, University of North Carolina, Chapel Hill, NC 27599-7135, USA.

OBJECTIVE: Inappropriate muscle activity is common following stroke. Paretic muscle activation may be influenced by non-paretic volitional activation. We examined the influence of non-paretic quadriceps activation on paretic quadriceps excitability. METHODS: Individuals with chronic stroke performed bilateral and unilateral (paretic and non-paretic) maximum voluntary isometric contractions. Peak torque and muscle activity were compared between conditions. An instrumented tendon tapper elicited a patellar tendon reflex of the relaxed paretic leg while the non-paretic leg was relaxed and pre-activated. The threshold to elicit a paretic quadriceps response was compared between conditions. RESULTS: During the bilateral MVIC, the paretic quadriceps generated less absolute torque, but greater relative torque than the non-paretic side when normalized to the respective unilateral condition (p<0.05). During reflex testing, the tendon tapping threshold to elicit paretic muscle and torque responses decreased with non-paretic activity (p<0.05). CONCLUSIONS: Concurrent non-paretic activation resulted in a relative disinhibition of the paretic quadriceps. The paretic limb's inability to remain inactive during isolated non-paretic contractions implies increased excitation or decreased inhibition of paretic motor pools, although the source remains unknown. SIGNIFICANCE: Unwanted muscle activity during reciprocal tasks (gait training) may be due to contralateral effects of non-paretic muscle activity. Copyright © 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.