Heat, humidity, dehydration & sunburn

article053You know the kind of heat that slams in to you like a 6-ton truck when you walk out of an air-conditioned room, leaving you immediately weakened?

As a tourist, it isn’t much of a problem. After a few days you get used to being sweaty, sticky and lethargic, symptoms alleviated by spending hours at the pool-side bar drinking iced tea. But when you’re a competitor at hot, humid and sticky event like Outdoor Quest, held in Sabah, Malaysian Borneo, the situation is considerably different; competitors must deal with high-intensity exercise over a prolonged period without the benefit of acclimatisation.

Following weather updates online from your home country, where it may be 36°C, you can be forgiven for thinking that 30°C is not that bad. But,have you ever noticed how 30°C feels hotter when it is humid than when the air is dry? This is where the humidex formula comes in.

The humidex value is derived by combining ambient temperature and the relative humidity of the air (how much moisture the air contains relative to how much it can contain at a certain temperature) to describe what the temperature feels like and how it is perceived in reality.

For example: the humidex value of 28°C/82F ambient temperature at 10% relative humidity is 28C/82F, at 40% it is 31°C/88F, at 60% it is 35°C/95F and at 85% it is 40°C/104F! These values have been applied to a scale that describes what the temperature really feels like outdoors in terms of the degree of comfort/discomfort experienced.

Humidex values: Degree of comfort or discomfort

< 29°C: Little or no discomfort
30°C to 34°C: Noticeable discomfort
35°C to 39°C: Evident discomfort
40°C to 45°C: Intense discomfort; avoid exertion
Above 45°C: Dangerous discomfort
Above 54°C: Heat stroke probable

So, how does this relate to an equatorial-based race?

Heat, which is produced by working muscles, must be eliminated from the body to maintain a relatively constant body temperature around 37°C/98.6F. Most of the heat generated is conducted in the blood stream to the skin where it is released into the environment. Although conduction and convection (transfer of heat from the warmer body to the cooler environment) are involved in heat elimination, evaporation of sweat is the most important and effective means of cooling.

This is where the crunch comes in as humidity is the greatest barrier to evaporation.

The rate of sweating is high in a humid environment but because the air is already substantially saturated, sweat cannot evaporate and thus cooling is substantially limited. The situation becomes more serious when the volume of sweat produced exceeds fluid intake and the person dehydrates. Cooling then becomes even more difficult, performance drops dramatically and heat injuries (heat cramps, heat exhaustion and heat stroke) are certain.

Heat cramps will often occur in the arms, legs or abdomen. They are thought to be caused by the depletion of salts and electrolytes from excessive fluid loss. Heat exhaustion is a little more severe. The competitor will likely have a headache and will feel weak and dizzy. Their blood pressure will be low, their pulse will be elevated and their body temperature will be higher than normal. Some time in the shade, a bottle of electrolyte fluid, plenty of water and salty food will see them back out on course.

Heatstroke is a life threatening. It results when the person is severely dehydrated, their body temperature is high and the body’s cooling mechanisms are shut-down. Most patients stop sweating, their pulse is rapid and weak, blood pressure drops and body temperature is greatly elevated. This is when damage to the brain, heart, lungs, kidneys and other organs may occur. Medical intervention must be immediate and effective or the person will die.

Hyponatraemia, overhydration with insufficient replacement of sodium, is probably not as much of a risk as the above heat injuries provided that electrolytes are adequately replaced.

Heat acclimatisation takes over a week, a luxury which most – if not all – competitors have not had. Thus, wearing light-coloured, moisture-wicking, loose-fitting, light-weight clothing and carefully monitoring their fluid and food intake will be crucial. But, while the competitors may be drinking a large volume of fluid, the problem in this environment is that the rate of sweat loss can easily exceed the rate of absorption of ingested fluids.

Compulsory 15-30-minute cool-down sessions, as implemented by Outdoor Quest, force the competitors to rest and re-hydrate before continuing and enable medical officers to keep an eye on the racers.

Finally, sunburn is a temporarily painful condition that, if severe, could see a competitor withdrawing from the race. Overexposure is also a serious long-term health risk; skin cancer (melanoma), premature aging of the skin and other skin problems, cataracts and other eye damage and immune suppression.

The ozone layer – more specifically, depletion of the ozone layer – is a critical environmental concern as it shields the Earth from the sun’s harmful ultraviolet (UV) rays, light of 290-400nm in wavelength. Ozone depletion, as well as seasonal and weather variations, cause different amounts of UV radiation to reach the Earth at any given time.

The UV Index considers the ozone layer thickness, UV incidence (incoming radiation level) on the ground, cloud cover (clouds reduce UV levels) and altitude (UV levels increase by 6% for every 1km of elevation gain). It does not include the effects of variable surface reflection (e.g., sand, water, or snow), atmospheric pollutants or haze, which may nearly double UV exposure strength. Thus, the UV Index, which ranks UV radiation levels on a 1-11+ scale, is a useful tool in assessing exposure risk.

UV Index Scale

  • <2: danger is low. Wear sunglasses and if you burn easily, cover-up and use sunscreen
  • 3-5: harm is moderate. Stay in the shade at midday and if outside, cover-up, use sunscreen and wear sunglasses.
  • 6-7: high risk of harm from unprotected sun exposure. Avoid outside exposure from noon till early afternoon. Use a sunscreen with a Sun Protection Factor (SPF) of at least 15 and wear a wide-brim hat and sunglasses to protect your eyes.
  • 8-10: Risk of harm is very high. Use a sunscreen of >SPF15, wear protective clothing (hat, long sleeves, sunglasses) and avoid sun exposure from noon to late afternoon. Unprotected skin will be damaged and can burn easily.
  • 11+: risk of harm is extreme. Minimise exposure during midday hours (10h00 – 16h00), apply sunscreen of >SPF15 every 2hrs and wear protective clothing. Unprotected skin will burn in minutes.

The risks associated with racing in an equatorial country in summer are high. Fortunately these can be managed. But even so, many competitors will suffer under such extreme conditions.

Author: Lisa de Speville