Dehydration and Hyperthermia First, understand that dehydration is your enemy. When you get dehydrated your blood volume drops, just like when you hemorrhage or give a blood donation. When you get dehydrated you may have trouble sweating and sending blood to your skin where it can help keep you cool. With dehydration keeping your temperature down to safe levels can be difficult. Heat injury can not only make you sick, it can cause muscle damage and destruction and kidney failure.
Heat injury is serious.
It can even kill. Study after study shows that even minimal dehydration can adversely affect your athletic performance. You must be sure you are fully hydrated before your matches, if you want to give yourself the best chance to win. Generally, the better the shape you are in, the fewer electrolytes you lose in your sweat. You may not even drink enough water even if you are already low on water.