The influence of eccentric contractions and stretch on alpha motoneuron excitability in normal subjects and subjects with spasticity.
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.
Rochester
L
L
Neuromuscular Research Unit, School of Physiotherapy, Faculty of Health Studies, Auckland University of Technology, Private Bag 92006, Auckland 1020, New Zealand.
Vujnovich
A
A
Newstead
D
D
Williams
M
M
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*