Vibration-Induced Frontal Postural Reactions in Humans Standing on Unstable Supports of Various Types

The authors studied the influence of the direction of support stability the vibration-induced frontal postural reactions of healthy humans during unilateral vibration of three lateral muscles, namely, the long peroneal muscle, tensor muscle of fascia lata, and abdominal external oblique muscle. The subjects stood on a movable blotter- shaped support. Its base was cylindrical or spheric; its height was 24 cm, and its base radius was 40 cm. The platform turn angle and sagittal and frontal horizontal shift of the upper part of the subjects' bodies were recorded. Reacting to vibrations, the subjects tilted their bodies contralaterally to the vibrated muscle, irrespective of the support type. These reactions were strongest when the subjects stood on a stable support and were weakest when the support was unstable. The reaction values were also influenced by the distance between the vibrated muscle and general center of gravity of the body. As a rule, all other things being equal, vibration-induced reaction strengthened when the stimulated muscle was closer to the center of gravity. The authors concluded that vibration-induced frontal reactions of a standing human depend on the support properties and reflect the features of the participation of the lateral muscles in the standing posture regulation. The information received from the lateral muscular receptors by the control system may be used in different manners, depending on the internal body–support interaction model formed by the CNS.