Evaluation of whole-body vibration in the sitting position by double-pulse holography and electromyography

Whole-body exposure to vibrations results mainly in mechanical effects on the living organism, which may include relative displacements, deformations or movement in or between different parts of the body. The response of the living organism is of the reflex action type. The musculature counteracts vibrations and stabilizes the body by an increase in muscle tone, especially under resonance-producing conditions when both striated and smooth muscles are affected. The most interesting phenomenon encountered when determining the biomechanical effects of vibrations on the human body is transmission. This study used a unique holographic technique by means of which the effects of vibrations on soft tissues and bones can be evaluated. The aim of the study was to investigate the manner in which the muscles of the back and vertebral column are affected by vibrations applied to the human buttocks in the sitting position. The subject was exposed to vibrations at two frequencies: 40 and SO Hz (vertical Z axis). Transmission of the vibrations along the subject’s back was recorded by means of double-pulse holography and electromyography. Evaluation of the vibration pattern showed that the vibrations are transmitted along the back all the way up to the neck and head. The pattern of vibration in the muscles of the back and vertebral column showed that the greatest effect was exerted on the lumbar region of the back and the area of transition between the thoracic and cervical regions.