Drinking Too Much During The Race
For decades, runners were taught that any amount of dehydration had a negative effect on performance and increased the risk for exertional heat illness, and were told to “drink as much as possible” to completely prevent dehydration. However, the human body was not designed to absorb large amounts of fluid during running. The jostling of the stomach that occurs on the run causes GI distress in runners who try to force down fluid.
What’s more, research has consistently shown that runners perform no worse and have no greater risk for heat illness when they simply drink according to their thirst, even though this typically results in only 65-70 percent replacement of sweat losses. While it is important to drink as often and as much as your thirst dictates during races, it’s a bad idea to drink more.