Dehydration is a huge factor when it comes to exercise performance.  As little as 2% dehydration results in decreased skin blood flow and sweat rate, which impairs the body’s ability to dissipate heat. This results in an increase in core body temperature and also an increased rate of muscle glycogen use. Your cardiac output decreases, you tolerate heat less, and the result is that you fatigue more easily. Dehydration means you get hotter and use up energy stores more quickly, and therefore your performance suffers. Check out our Hydration Guide at