title: Stretch-sensitive paresis and effort perception in hemiparesis.
abstract: In spastic paresis, stretch applied to the antagonist increases its inappropriate recruitment during agonist command (spastic co-contraction). It is unknown whether antagonist stretch: (1) also affects agonist recruitment; (2) alters effort perception. We quantified voluntary activation of ankle dorsiflexors, effort perception, and plantar flexor co-contraction during graded dorsiflexion efforts at two gastrocnemius lengths. Eighteen healthy (age 41 ± 13) and 18 hemiparetic (age 54 ± 12) subjects performed light, medium and maximal isometric dorsiflexion efforts with the knee flexed or extended. We determined dorsiflexor torque, Root Mean Square EMG and Agonist Recruitment/Co-contraction Indices (ARI/CCI) from the 500 ms peak voluntary agonist recruitment in a 5-s maximal isometric effort in tibialis anterior, soleus and medial gastrocnemius. Subjects retrospectively reported effort perception on a 10-point visual analog scale. During gastrocnemius stretch in hemiparetic subjects, we observed: (1) a 25 ± 7 % reduction of tibialis anterior voluntary activation (maximum reduction 98 %; knee extended vs knee flexed; p = 0.007, ANOVA); (2) an increase in dorsiflexion effort perception (p = 0.03, ANCOVA). Such changes did not occur in healthy subjects. Effort perception depended on tibialis anterior recruitment only (βARI(TA) = 0.61, p < 0.01) in healthy subjects (not on gastrocnemius medialis co-contraction) while it depended on both tibialis anterior agonist recruitment (βARI(TA) = 0.41, p < 0.001) and gastrocnemius medialis co-contraction (βCCI(MG) = 0.43, p < 0.001) in hemiparetic subjects. In hemiparesis, voluntary ability to recruit agonist motoneurones is impaired--sometimes abolished--by antagonist stretch, a phenomenon defined here as stretch-sensitive paresis. In addition, spastic co-contraction increases effort perception, an additional incentive to evaluate and treat this phenomenon.
authors.affiliation: AP-HP, Laboratoire Analyse et Restauration du Mouvement, Service de Rééducation Neurolocomotrice, Hôpitaux Universitaires Henri Mondor, Université Paris Est Créteil (UPEC), 50, av du Maréchal de Lattre de Tassigny, 94010, Créteil, France, mariaconcetta.vinti@gmail.com.
authors.forename: Maria
authors.initials: M
authors.lastname: Vinti
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bayle
authors.forename: Emilie
authors.initials: E
authors.lastname: Hutin
authors.forename: David
authors.initials: D
authors.lastname: Burke
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Gracies
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D035002:Lower Extremity / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010291:Paresis / Q000503:physiopathology*; D010465:Perception