Effects of the asymmetric tonic neck reflex and high-frequency muscle vibration on isometric wrist extension strength in normal adults

Abstract

The effects of the asymmetric tonic neck reflex and high-frequency muscle vibration on isometric wrist extension strength were studied in 150 normal, right-handed adults between the ages of 18 and 40. Subjects were randomly assigned to one of five groups. From data collected from two control groups, we determined any confounding effects of fatigue, experimental learning, or weight of the vibrator in contact with the skin surface overlying the wrist extensor muscle bellies. From measurements taken from three experimental groups, we determined the individual and combined effects of the asymmetric tonic neck reflex and vibration. The reflex was elicited with active head rotation. Strength significantly increased with active head rotation toward the extending wrist; active head rotation away from the wrist significantly decreased strength. Vibration of the extensor surface of the forearm with the head in neutral significantly increased strength. The combination of active head rotation toward the extending wrist and vibration of the extensor surface resulted in a greater increase in strength than did either technique individually.