Modulation of the triceps surae H-reflex with training.
Thirteen neurologically healthy adults were asked to balance on a specially designed balance board. This board allowed rotation in the sagittal plane only. Muscle activity of the triceps surae and tibialis anterior was sampled at 2 kHz and recorded. When the subject was balanced, soleus H-reflexes were elicited in the right leg with a constant-current stimulus pulse. The peak to peak amplitude of the soleus H-reflex served as the perturbation to the subject's balance as well as the dependent variable in question. Subjects performed three blocks (7 H-reflexes/block) of standing control trials with the balance board supported, and seven blocks of balancing trials. Prior to each block, maximal M-waves were recorded to ensure electrode stability across blocks. Results indicated that the subjects were able to significantly reduce (p < .001) the gain the soleus H-reflex while balancing and after the balance training. As a group, the subjects decreased their peak to peak amplitude of the soleus H-reflex by 26.2 percent from the initial standing block to the last balancing block. Moreover, subjects were also able to significantly reduce the gain of their standing control H-reflexes, supporting the notion of longer-term adaptability of the spinal stretch reflex. It is concluded that the progressive reduction in the H-reflex gain with short-term training may represent functional adaptation in the central nervous system.
Indiana University School of Medicine, Department of Physical Therapy, Indianapolis 46202-5119.
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Trimble
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Koceja
D000293:Adolescent; D000328:Adult; D001132:Arm / Q000294:innervation / Q000502:physiology; D001696:Biomechanical Phenomena; D004558:Electric Stimulation; D004576:Electromyography; D006801:Humans; D009048:Motor Skills / Q000502:physiology*; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009132:Muscles / Q000294:innervation / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D012026:Reflex, Stretch / Q000502:physiology*