TISSUE DISPLACEMENT IS A CAUSATIVE FACTOR IN VIBRATION-INDUCED MUSCLEINJURY

The early skeletal muscle response to vibration stimulus at two differ ent displacement levels was examined. Twelve rats were anaesthetized a nd the hind limb was exposed to vibration, 80 Hz, 63 mu mrms (root mea n square) (group 1) and 40 Hz; 130 mu mrms (group 2) for 5 hours/day f or 2 days, Cross-sectional areas of vibrated muscle fibres were signif icantly larger in group 2. Sizes of different fibre types were differe ntly affected: the slow-twitch type 1 fibres were significantly enlarg ed in both groups, while the fast-twitch type 2 fibres demonstrated a mixed response pattern, Centrally positioned muscle fibre nuclei incre ased significantly after vibration in group 2, It is concluded that th e level of tissue displacement is a crucial factor for development of vibration-induced muscle injury.