Trunk position sense in the frontal plane.

Twenty healthy volunteers (ages 18 to 25 years) were tested for their ability to sense the lateral position of the top of their thoracic spine. When moved slowly from side-to-side in the frontal plane with vision occluded and pelvis immobilized, they could sense the position of a midline point on the skin at the T1 level to within 3 mm of a mean center position in relaxed standing tests, and to within 9 mm in supine tests. When subjects centered themselves actively, or additionally, contracted trunk flexor or extensor muscles to predetermined levels of activity, no increase in trunk positioning accuracy was found. The effect of a lateral pelvic tilt or lateral trunk moment had little effect on trunk positioning accuracy, but always induced a characteristic trunk offset. No differences were found in any of these results between males or females, or gymnasts or nongymnasts.