The electromyographic response to sudden stretches of limb muscles in normal human subjects

The electromyographic (EMG) activity following a sudden stretch applied to wrist flexor or extensor muscles was investigated using a method which enabled the individual records and cumulative results of 30 trials to be observed simultaneously. The results showed that in each case the spinal reflex EMG burst was followed by one or two additional reflex bursts. The second of these latter bursts, when present, occurred in one of two distinct latency ranges. Thus, three distinct latency ranges were observed for reflex bursts following the spinal reflex burst. A possible explanation for these results is that there are three distinct long-loop reflexes, one or two of which may be active following a muscle stretch. The present results do not distinguish whether any or all of these long-loop reflexes are segmental or supraspinal in origin.