Inter-trial variation of soleus H reflex in humans: implication for supraspinal influence.
Inter-trial variation in soleus H reflex amplitude for different effort modes, elicited at different test-stimulus intensities, was studied in fifteen healthy subjects. Regardless of test-stimulus intensity, weak isometric plantarflexion and dorsiflexion at 20% of maximum voluntary contraction caused significant potentiation and depression of the H reflex amplitude. In addition, both facilitation and inhibition of the soleus H reflex was associated with considerable inter-trial variability of the H reflex amplitude that varied proportionally with test-stimulus intensity. As inter-variability of the H reflex was independent of that of M response, the results indicate that: 1) supra-spinal input influences loop-gain fluctuations of the monosynaptic-reflex arc; and 2) smaller test stimuli may be more efficacious for exploration of motoneuronal excitability because of reduction in variability in H reflex amplitude.
Hwang
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IS
Department of Physical Therapy, College of Medicine, National Cheng Kung University, Tainan 701, Taiwan. ishwang@mail.ncku.edu.tw
Tsai
I Y
IY
D000293:Adolescent; D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D014644:Genetic Variation / Q000502:physiology*; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D013131:Spine / Q000502:physiology; D013997:Time Factors