Water deprivation decreases strength in fast twitch muscle in contrast to slow twitch muscle in rat

The effects of dehydration on muscle performance in human are still contradictory, notably regarding muscle force. The effect of water deprivation (WD) on mechanical properties of skeletal muscle, and more precisely its impact on slow and fast muscles, remains largely unknown. The aim of this study was to determine for the first time whether WD leads to changes in contractile properties of skeletal muscle and whether these changes were muscle-type-specific.Sixteen-week-old male rats were assigned to either a control group (C) with water or a 96-hour WD group. At the end of the period, twitch and tetanus properties, as well as biochemical and structural analysis, were performed on soleus (SOL) and extensor digitorum longus (EDL) muscles.Absolute twitch (Pt) and tetanic (P0 ) tension were, respectively, 17% and 14% lower in EDL of WD rats as compared with C rats, whereas unexpected increases of 43% and 25% were observed in SOL. Tensions normalized with respect to muscle mass were not affected by WD in EDL, whereas they were increased by more than 40% in SOL. A 96-hour WD period leads to a decrease in fibre cross-sectional area and absolute myofibrillar content only in EDL.It is hypothesized that differences in the results between slow and fast muscles may come from (i) a muscle-type-specific effect of WD on protein balance, EDL showing a greater myofibrillar protein breakdown and (ii) a greater sensitivity to osmolality changes induced by WD in EDL than in SOL.