"One of the big concerns from this change though is that some doctors are claiming you don't rehydrate fully in a short period of time this way. Fighters weigh

"One of the big concerns from this change though is that some doctors are claiming you don't rehydrate fully in a short period of time this way. Fighters weigh in the day before a fight, so they're peak dehydrated roughly 24 hours before they fight. There are claims that it takes the brain many days to fully rehydrate after a weight cut if you're not using IV's, so people paying attention in the sport are really worried that brain injuries are going to start going up." I have always been skeptical of this notion that rehydration takes hours or days or whatever. First of all, practical experience shows that mucus, urine, sweating[1], etc. very quickly revert to full hydration. You can go from dark yellow urine to clear urine in less than two hours. Second, what mechanism could there possibly be to restrict water absorption in your body while dehydrated ?[2] I don't think you could slow down rehydration if you tried to[3]. Your body doesn't have to digest it and it can transport nearly immediately outward to every tissue (as evidenced by nasal mucus production which reverts as quickly as your urine color does). I think it's just bro-science and it's surprising that it is so persistent (I have heard it in the gym, at basic training, in the fire service, etc.) because immediate, practical evidence contradicts it. [1] I am not talking about heatstroke, etc., which are separate issues. [2] The only thing I can possibly think of is stuffing yourself with very absorptive food prior to rehydrating ... which would be odd. [3] Assuming normal water with normal mineral content. Obviously, distilled water will cause problems.