REFLEX ACTIVITY IN THE SPINAL EXTENSORS

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Abstract
Electromyographic studies with electrodes placed in and over the thoracic extensors, on human subjects at rest, indicated the presence of activity in these muscles in certain instances. The active ("abnormal") areas could be selected by palpation, because they presented a higher resistance to pressure deformation than did the quiet ("normal") ones. Localized motor activity was seen in the abnormal area in 21 of 25 expts. when simultaneous recording from the normal area failed to show activity. A single active unit in the abnormal area could sometimes be inhibited by slight voluntary contraction of the abdominal wall, shallow respiration of the abdominal type, counting or talking aloud and by swallowing. The motor unit activity demonstrated in abnormal areas is similar in frequency, asynchronism and recruitment to the stretch reflex except that it was observed when the subject was completely relaxed, in the resting period of the respiratory cycle, and with the head in the mid-line. The absence of gross visceral disease in all subjects and the presence of posture abnormality indicate that the motor activity is reflex, and that the afferent limb of the reflex arc probably consists of proprioceptors from segmentally related muscles, tendons, joints or bones.

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