title: The influence of eccentric contractions and stretch on alpha motoneuron excitability in normal subjects and subjects with spasticity.
abstract: Application of eccentric contractions and muscle stretch are clinically effective in reducing spasticity and increasing ROM (7). This may be explained by a change in the excitability of motoneurons supplying the spastic muscle. Excitability of motoneurons can be indirectly assessed using the H-reflex. Experiments were performed on 20 normal subjects and 17 subjects with spasticity resulting from neurological disorder. Subjects were seated in a secure position and the ankle joint was moved from 30 degrees plantarflexion to 20 degrees dorsiflexion at a velocity of 30 degrees/sec. Sixty eccentric contractions of the triceps surae muscle were performed using a Kin-Com dynamometer (Chattanooga Corp, Tennessee). Two protocols were used: (1) eccentric contractions only, and (2) eccentric contractions with a 5s stretch of the relaxed triceps surae after each contraction. Two sets of 10 H-reflexes were collected from the soleus muscle before (trial 1 & 2) and after (trial 3 & 4) eccentric and eccentric + stretch protocols. The mean peak to peak H-reflex amplitude was calculated for each trial and compared using ANOVA. Eccentric contractions resulted in a significant and maintained increase in the H-reflex in neurological compared to normal subjects (P < 0.05). Eccentric contractions in subjects with spasticity resulted in an increase in motoneuron excitability which may assist in corticospinal activation of motoneurons during voluntary movement. The eccentric + stretch protocol, resulted in a decrease in the mean amplitude of H-reflexes in neurological subjects, however, this was not significant. The application of a stretch following eccentric contractions decreased motoneuron excitability and may thus be beneficial to decrease spasticity whilst strengthening muscle.
authors.affiliation: Neuromuscular Research Unit, School of Physiotherapy, Faculty of Health Studies, Auckland University of Technology, Private Bag 92006, Auckland 1020, New Zealand.
authors.forename: L
authors.initials: L
authors.lastname: Rochester
authors.forename: A
authors.initials: A
authors.lastname: Vujnovich
authors.forename: D
authors.initials: D
authors.lastname: Newstead
authors.forename: M
authors.initials: M
authors.lastname: Williams
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D009128:Muscle Spasticity / Q000209:etiology / Q000503:physiopathology*