24 April 2006

Heat stroke and dehydration woes

The 11th series of the ever-popular Survivor Series started on Tuesday, and already after the first episode, there are lessons we can learn from the Survivors, writes DietDoc.

The 11th series of the ever-popular Survivor Series started on Tuesday, and already after the first episode, there are lessons we can learn from the Survivors.

This first week started off with typical drama. The newly arrived Survivors were divided into two tribes. Each tribe was given a previous Palau Survivor (Bobby John and Stephenie) to accompany them on an 11 km struggle through the jungle to their camps.

High drama
After just a few hours, the relentless heat, soaring humidity and strenuous exertion was taking its toll. One by one, the biggest, toughest men in the Nakum tribe were collapsing in all directions.

Strong, brawny men with bulging muscles were huddled on the ground groaning with cramps, or vomiting helplessly. Bobby John, for example, was so weak that he could hardly walk and at one stage it looked as if he would develop convulsions.

What caused these collapses?
These alarming occurrences were most probably the result of extreme heat exhaustion, heat stroke and dehydration.

While most readers are not likely to be exposed to such conditions, athletes, particularly long-distance and marathon runners, are often subjected to similar stresses – extreme exhaustion, extreme heat and extreme dehydration. The TV coverage of the first-aid tent after a Comrades marathon features many runners who have similar symptoms.

In Lore of Running, Prof Tim Noakes of UCT describes many of the factors that were playing a role in the jungles of Guatemala.

According to Noakes, blood circulation during exercise changes significantly. More blood flows through the muscles, the heart increases its pumping action and blood is diverted from non-essential parts of the body to the muscles and the skin.

The blood that is pumped through the strenuously working muscles heats up, which means that the entire body, and the skin in particular, also heat up. The temperature rises and the human body tries to cool itself down.

Air circulating around the body will remove some of the heat via convection and sweat produced by the body will evaporate to produce a cooling effect. Another complicating factor during intense exercise is that blood flow to the muscles gets preference and less blood flows to the skin for cooling purposes.

In other words, heat production in the body increases, while the ability to cool down decreases, which will in turn raise the body temperature even further, sometimes to dangerous levels.

Problems in the jungle
The soaring heat, absence of wind, high humidity and lack of water for cooling the Survivors down, contributed to the collapse of the men. All these environmental factors were stacked against the Survivors – there was no cooling breeze to remove body heat and promote evaporation of sweat, and no sea to douse their burning bodies in.

These are also the reasons why the Survivors in Guatemala suffered so badly, and probably will continue to suffer more than Survivors on islands surrounded by the sea where there is always a breeze and the possibility of cooling off one's body rapidly in the water.

In an attempt to reduce its temperature, the human body will produce sweat in large quantities. Such large losses of body water cause dehydration. Added to this, the Survivors who collapsed were all vomiting and, therefore, losing even more body fluid.

Research conducted on runners found that runners who did not drink sufficient water during strenuous exercise, lost up to 5% of their body weight in the form of water.

The most important rule to keep in mind if you are doing strenuous, exhaustive exercise, particularly in hot climates, is to drink water regularly. Marathon runners drink between 500 to 1000 ml of water every hour.

To do this, each Survivor would have had to carry between 5,5 to 11 litres of water for their journey. Judging by the size of their water containers, the Survivors did not carry enough water to meet their needs and suffered the consequences.

Salts and glucose
Noakes also points out that research over many years has identified the need for including electrolytes and glucose in the water consumed by athletes to restore losses suffered by the body due to excessive sweating and exhausting exercise.

As far as I could see, the Survivors Guatemala only had plain water at their disposal and although those that did not vomit may not have lost appreciable amounts of potassium or sodium, all of the Survivors would have been badly depleted of glucose as an energy source.

How to prevent heatstroke and dehydration
To prevent heatstroke, it is important for athletes to either avoid exercising when it is very hot and humid, or to train under hot, humid conditions until they are acclimatised. This, of course, the Survivors did not do. They had no option but to take on the heat and humidity without previous acclimatisation.

Furthermore, it is important for athletes who compete in long events to replenish their water, electrolyte and glucose losses. Use any one of the energy drinks currently available in South Africa, such as EnerG, Powerade, Lucozade or Energade during the event.

Basically, these energy drinks contain water, some sodium and potassium, and glucose in the form of polymers to slow absorption. Athletes should experiment while training to find the energy drink that agrees best with them, because some athletes may find that certain of the products can cause stomach cramps and winds.

Drink regularly and, if possible, cool down by splashing your head and body with cold water. The poor Survivors – they had none of these options and their breakdowns made dramatic, if dangerous, viewing.

I can't wait to see how the Survivor Guatemala competitors cope with the extreme conditions they have to face, and will keep you informed about their dietary problems as the series continues. – (Dr Ingrid van Heerden, DietDoc)

(Noakes T (1991). Lore of Running. Oxford University Press, Cape Town.)

Any questions? Ask DietDoc.


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