In any length running race, as short as 5k, there will be multiple water stops for the participants. Research in exercise physiology has shown that when a person is running more blood is sent to the working muscles and as a result less blood is sent to the organs, so typically anything eaten or drank while running will not be digested in time to be useful for the run and that is why it is so important to be properly hydrated before the race starts.. Knowing this, I tend to think that water stops in short races are silly, but now that I am training for a marathon, which places different demands on the body, I wonder about the role of hydration and distance running.
Before the 1970s, people believed that it was best not to drink at all during exercise (Noakes, 2007). The initial push for lots of water was led by a belief that the more water the better, until there were a few significant cases of hyponatremia, especially in slower marathon runners. Since then, organizations interested in running have been reviewing their hydration guidelines.
On the one hand there is the possibility of dehydration. The physical demands of running a marathon can cause significant water loss through sweat, which in turn can impair performance (Cheuvront, Montain and Sawka, 2007). One way dehydration impairs running performance is through decreased cardiac output. As people sweat and lose water, they also lose blood volume which leaves less for the body to use (Kenefick and Sawka, 2007). On top of impairing performance, dehydration can be dangerous. It can cause fatigue, increased body temperature, cramps, confusion and even unconsciousness (Mayo Clinic, 2009).
The main problem with drinking too much water during physical activity is the potential for hyponatremia, which is basically a low concentration of sodium in the blood caused by all the water diluting the blood. Hyponatremia can be very dangerous and over the past few years the number of occurrences has been increasing in events like the marathon (Hsieh, Roth, Davis, Larrabee and Callaway, 2001). In a study by Hsieh, et al. (2001), in one marathon the researchers found that 5.6% of participants needed medical treatment for hyponatremia.
According to Cheuvront, et al. (2007), water needs vary greatly between individuals based on the distance of the run, the pace at which they run, the weather and the individuals body mass. That being said, it is difficult to create one standard that is good for everyone. The guideline that seems most logical is the one from USA Track and Field. The USA Track and Field guideline suggests that thirst should drive water consumption (Levine and Thomson, 2005). This makes sense because our bodies are pretty good at telling us what we need and this process has been improved and adapted over many years.
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