O-20 The effect of immobilisation and whole body vibration on MHC isoforms in rat skeletal muscle

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Skeletal muscle is a plastic tissue and has an adaptive capability to modify its size and function as a response to a change in environmental and physiological stress. Reduced activation of skeletal muscle or immobilisation influence the phenotypic expression of muscles by reducing slow myosin heavy chain (MHC) isoforms whereas fast isoforms increase. On the other hand, increased muscle activation gives rise to MHC shift from fast to slow isoforms. Application of whole body vibration (WBV) attracted widespread attention during last a few years is a focus of our interest as a model of activity. In the unloading models like hindlimb suspension, the transformation of MHC isoforms from slow to fast is observed widely in antigravity muscle which has consist of mostly slow MHC isoforms. On the other hand, the effect of unloading on MHC isoforms for non-antigravity muscles is not known. For this purpose, the effect of immobilisation and whole body vibration on MHC isoforms in plantaris muscle have been examined. Four month old Wistar type female rats have been randomly separated into five different groups (n = 6, each group); control, two weeks immobilisation, two weeks immobilisation followed by one week remobilization, two weeks immobilisation followed by one week of WBV and just one week of WBV. Immobilisation has been applied by bilateral casting of legs when foot is plantar flexion position. WBV application has been applied for 20 mins daily duration for one week at 45Hz and 3mm amplitude. There was not any significant change in MHC expression among groups (p > 0.05). These results show that neither two weeks of immobilisation nor one week of whole body vibration (WBV) has any phenotypic changes on plantaris muscle.