Running marathons is not only about training and good diet. Fluid intake is equally vital. Drinking enough fluids is essential, as is ensuring they are the right kind of fluids. Water, energy drinks, caffeine drinks and alcohol all have an effect on performance.
Ensuring good hydration is important for a number of reasons. If there is not enough water in the body to produce sweat body temperature will rise above 41oC - the limit above which there is the risk of heat stroke. Similarly, dehydration will cause the blood to thicken, slowing the circulatory system. This means that the heart will need to work harder to push this sluggish blood around the body. In turn, oxygen will take longer to be transported around the body to muscles where it is needed.
It should be noted that too much water can also cause problems. In the 2007 the Flora London Marathon, David Rogers, a 22-year-old fitness instructor collapsed shortly after finishing the race. He later died in hospital, the cause of death being put down to drinking too much water. The excessive amount of water diluted body nutrients so much that they were below a safe minimum level, with unfortunately lethal effect.
There are two main types of energy drink, isotonic and hypotonic. Isotonic drinks contain carbohydrate particles at the same concentration as the body's fluids so that they pass into the bloodstream at the same rate as water. In comparison, hypotonic drinks contain carbohydrate at a concentration less than that of body fluid. This means that it absorbed into the body more quickly, speeding up the rehydration process.
Energy drinks are now commonly given out on marathons. Approximately every 5 miles you would be expected to be offered these energy-giving fluids, typically Powerade or Lucozade. For many runners this is considered to be a real life-saver, preventing them from 'hitting the wall' and allowing them to reach the finish line.
"Caffeine stimulates the central nervous system, making some people feel more awake and giving the others the jitters."
By causing such a change, it would seem safe to assume that drinking coffee or any other caffeinated product has the advantage of stimulating athletic performance. However, there are actually numerous disadvantages to such action. Further, many national athletic bodies go as far as banning the use of caffeine products because of its detrimental effects.
Caffeine drinks have been associated with two health problems - raised blood pressure and gastroenterological (stomach) damage. Increased blood pressure will put extra strain on an already hard-working heart during any run. Similarly damage to the stomach by coffee will be elevated when an athlete sets off on their run - the stomach contents being constantly battered up and down. So while no gain is achieved from the initial caffeine rush, a runner will present themselves with the chance of further damage which will only hinder their efforts.
Dehydration can also be caused by caffeine. Coffee and other caffeine drinks cause water to be removed from the body, predominantly by urinatioin. In a race, or in training, this will have the resulting effect of discomfort and/or increased thirst, either of which will hinder your performance.