Effect of head-neck position on elbow flexor muscle torque production.

The purpose of this study was to investigate whether the tonic neck reflex affects elbow flexor muscle torque production in healthy, young adults and which head-neck (H-N) positions have the greatest influence. Forty-eight male and female students between the ages of 18 and 35 years volunteered as subjects. Head-neck positions involving the sagittal and horizontal planes and combinations of these were tested. The nondominant hand was used to apply tension to the lever of an isokinetic analyzer under both isometric (static) and isotonic (dynamic) conditions. Peak torque was determined for each H-N position under each condition. Differences in peak torque were elicited more easily from the female subjects than from the male subjects. Head-neck rotation (horizontal plane) appeared to have a greater influence on elbow flexor muscle torque production than movements in the sagittal plane, particularly when movements in the two planes were combined. We concluded, therefore, that H-N position must be considered during rehabilitation of the upper extremity.