Respiratory and Head Position Influences on Late Stretch Reflexes

Abstract

The purpose of this study was to determine the relative effects of the asymmetric tonic neck reflex (ATNR) and of respiration on the upper limb, as measured by their influence on the stretch reflexes. Long latency stretch reflexes (M2 and M3) were induced in elbow muscles of human subjects. The subject's right forearm was strapped into a manipulandum. The forearm was perturbed with a torque test pulse at a fixed interval prior to an intended forearm movement. It was found that both the M2 and M3 reflexes, in triceps or brachialis muscles were significantly increased when perturbations were delivered during inspiration as compared to expiration. Rotated head positions to the right or left could also significantly alter reflex magnitude but there was no consistent pattern among subjects. The clinical implications of these findings are discussed.