T ISSUE D ISPLACEMENT IS A CAUSATIVE FACTOR IN V IBRAT ION- INDUCED MUSCLE IN JURY

The early skeletal muscle response to vibration stimulus at two different displacement levels was examined. Twelve rats were anaesthetized and the hind limb was exposed to vibration, 80 Hz, 63 ~tmrms (root mean square) (group 1) and 40 Hz; 130 Itmrms (group 2) for 5 hours/day for 2 days. Cross-sectional areas of vibrated muscle fibres were significantly larger in group 2. Sizes of different fibre types were differently affected: the slow-twitch type 1 fibres were significantly enlarged in both groups, while the fast-twitch type 2 fibres demonstrated a mixed response pattern. Centrally positioned muscle fibre nuclei increased significantly after vibration in group 2. It is concluded that the level of tissue displacement is a crucial factor for development of vibration-induced muscle injury. Journal of Hand Surgery (British and European Volume, 1996) 21B: 6:753-757 Hand arm-vibration syndrome (HAVS), i.e. the com-plex of peripheral neurological, circulatory and musculo-skeletal dysfunctions occurring in vibration-exposed operators, has been widely studied and recently reviewed (Gemne et al, 1993; Pelmear et al, 1992)