Do not over hydrate
Fatalities do occur in marathons. The worldwide average is one fatality for every 3 million marathon km run. It doesn’t sound high and indeed it isn’t. However with 50,000 runners cover 42 km each in the New York marathon that adds up to 2 million km. So New York can expect two fatalities every 3 years.
However, if I were to line up 3 million runners and get them to run just one km each, the chances are that one of them would die from some reason not related to running a km.
The overwhelming majority of marathon fatalities (>90%) are due to a previously undetected heart condition. Marathon conditions place extra strain on the heart which causes the defective heart to fail. Warmer or humid conditions place even more strain on the heart as it has to work that much harder to keep the body cool, resulting in a higher frequency of fatalities.
However, some fatalities do occur related to de-hydration, heat stroke and over hydration. Of these, over hydration is by far the highest risk.
Back ground.
Prior to the 1960s runners paid little attention to hydration. It was almost considered to be unsporting to take on board water during an endurance event. Then a study revealed that runners at the end of a race who had lost most weight, through de-hydration had the highest core body temperature. It was incorrectly assumed that dehydration caused hyperthermia, (That is increase in body temperature). In the extreme, if body temperature rises above 42c, hyperthermia can result in heatstroke and death. The advice to runners changed to “Drink everything in sight.” “Don’t wait until you are thirsty” As always it took runners a while to catch on but by the 1980s everyone was drinking to excess.
The body temperature rises during exercise. The body’s natural method of dealing with this is to sweat. As sweat evaporates from the surface of the body it takes heat out of the body. This leads to de-hydration. So, dehydration is a result of hyperthermia, not the cause of it. It is important to take on water to replace lost fluid.
By the 1980s a new problem was observed, Hyponatremia. That is low sodium concentrations in the blood. It is extremely dangerous and has been linked to many fatalities. A study of a sample of runners in the Boston marathon found that 1 in 8 had hyponatremia. The cause was found to be due to over hydration. The blood sodium level becomes diluted due to over hydration.
Advice has now changed to “Drink according to your thirst” “Do not drink more than 800 to 1000ml per hour” “Drink small amounts frequently, say 200ml every 15 minutes.
Heat Stroke
Heat Stroke is almost non-existent amongst runners. This is because, long before your body temperature reaches danger levels you will find it too hard to run. If you stop running or collapse your body will start to cool down. However, if the body’s natural cooling mechanism has been upset due to taking sports enhancing drugs or medication (including anti-inflammatory drugs) then heat stroke can occur. The treatment is to cool the body down as quickly as possible. Submersing the body cold water or fanning the body is recommended. If it is sunny then get some shade over the body, but do not move the body. This can be fatal. If the runner is vomiting then turn the body onto its side so that the runner doesn’t choke on the vomit.
Dehydration
Dehydration is best treated by giving the runner water to drink, if they are conscious and able to take it. Otherwise the standard procedure is to apply an intravenous drip.
Over Hydration, Hyponatremia
This is by far the most dangerous condition for runners. It is the dilution of sodium levels in the body due to taking in too much fluid. Those most at risk are small runners and slower runners.
Small runners lose body heat due to radiation at a far greater rate than larger runners. Hence they sweat less and dehydrate less. So they do not need to take on so much water during an event.
Slower runners dehydrate less than faster runners and hence do not need to take on so much water. Also there is the danger that because they are out on the course for longer they may drink more.
The symptoms of Hyponatremia are very similar to dehydration or heat stroke. Hence it is often wrongly diagnosed and treated with a regular intravenous drip, which can be fatal. The correct treatment is to apply a drip of at least 3% sodium content. A person suffering from Hyponatremia may well vomit clear fluid.
More information
I have placed a pdf file on the web site which has more detailed information including recommendations from the top marathon sites. Unfortunately Dubai Marathon advice is not in touch with latest thinking.
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