[Muscle post-effects and upright standing in healthy subjects and patients with sensory-motor integration disorders]

We compared the upright standing in 7 patients with sensory-motor disorders and 7 healthy subjects (control) before and after 30-s involuntary neck muscle contraction. A trajectory of the center of pressure was recorded during 30-s standing with the eyes open, eyes closed and standing on a foam-rubber with the eyes open. As compared to healthy subjects, patients exhibited an increased body sway area during standing with the eyes open on both the firm surface and foam-rubber and a backward shift of the center of pressure during standing with the eyes both open and closed. Closing the eyes affected the upright standing of patients to a lesser extent than standing of healthy subjects. Involuntary neck muscle contraction within 30 s elicited a backward shift of the center of pressure in healthy subjects, especially during standing with the eyes closed, and a decrease in the length of the center-of-pressure trajectory, especially of its frontal component during standing on the foam-rubber. In patients, a post-effect of the neck muscle contraction manifested itself as a decrease in the body sway area during standing on the foam-rubber and relative increase in the frontal component of the center-of-pressure trajectory during standing with the eyes closed. The results suggest that the upright standing of patients with sensory-motor disorders is more sensitive to somatosensory than visual input, and 30-s neck muscle contraction approach their postural stability to the age-matched control.