[Switching effect in the system of equilibrium regulation in man]

Postural reactions evoked in human by bilateral vibration of calf muscles were studied under different conditions: sitting without the feet contact with a support; sitting in an unstable position on the edge of the chair; sitting under conditions of the foot contact with different types of supports (rotating disk, suspended platform, etc.); standing with an asymmetrical load applied to the trunk. It has been shown that local vibration of calf muscles can evoke activation not only of the vibrated muscle or of its antagonist (local effects), but also of extensors and flexors of the knee joint (non-local effects), or of the remote muscular groups, involved in different postural synergies. The concrete pattern of muscle activation is determined by several factors, the most important being the relative position of the body links and interaction of feet with a support. The mental image of the body configuration in the system of internal representation is also very significant.