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

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.

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.

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).

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.

Unwanted muscle activity during reciprocal tasks (gait training) may be due to contralateral effects of non-paretic muscle activity.