This article is on heat and humidity concerns for track and field meet organizers and athletes. It will deal with environmental factors and the effect on human performance. In this era of global warming, this has taken on added significance. This is further compounded by the fact that we live, train and compete in a warm environment.
We humans are among a group of animals that maintain a fairly constant core body temperature, despite changes in the ambient temperature. Humans maintain a core body temperature of 37 degrees centigrade +/- 1 degree. T his tight control (thermo-regulation) is regulated by a centre in the brain called the hypothalamus. This core temperature represents a balance between heat production and heat loss which is affected by both internal and external sources.
Heat gain is affected by factors that are both internal and external to the human body. The things affecting heat gain internally are heavy exercise, illnesses and drugs e.g. anti-inflammatories like cataflam and alcohol. The external factors are the ambient temperature, humidity, air movement (the wind) radiant heat from the sun and warm and cold surfaces.
The body’s ability to lose heat is affected by environmental factors such as the ambient temperature, the relative humidity and the air currents. It is also affected by the individual’s level of fitness and the degree of heat adaptation. Heat exchange occurs between the body and the environment and does so continuously. Some factors are bi-directional (conduction, convection and radiation) and others are uni-directional e.g. metabolic heat (increases the load) and evaporation (reduces the load). It is the interplay of these factors that determines the body temperature.
When the net heat gain is positive, body temperature rises and when it is negative the body temperature falls. When we exercise, we increase the metabolic load as only 25% of the muscle energy is used for movement and the rest 75% becomes heat for dissipation. After a few minutes of exercise, body temperature including core body temperature will rise. An increase in the core body temperature has the following effects on running performance. It improves it in the sprints and gradually impairs it the longer we run. When we exercise in the heat we get a sensation of heat intensity, the output of the heart increases and the breathing rate also increases. Blood flow is redirected to the skin to facilitate heat loss. The rate of sweating is also increased. Over time a tolerance is developed for elevated core body temperatures.
Wet bulb globe temperature (WBGT) is defined as a measure of heat stress in direct sunlight. It takes into account the ambient temperature, the humidity, the wind speed and solar radiation. It is a measure of the body’s ability to lose heat under any given environmental condition. It is measured by a device that is commercially available for under US$100.00. The device essentially uses 3 thermometers to give a single value and estimates the environment’s capacity to cool an individual by evaporation. The thermometers measure relative humidity (wet bulb), ambient temperature (dry bulb) and solar radiation (black globe). The reading of the WBGT is used to quantify the heat risk into low risk, moderate risk, high risk and very high risk. At the different risk levels meet managers in conjunction with their medical teams take certain actions. At the very high risk level, distance races are postponed or canceled. At a high risk level, runners are to be alerted especially those that are sensitive. For a moderate or low risk level normal precautions are taken.
How do we prevent heat injury? Preparation for this starts before race day. We can undergo heat adaptation. This can occur in seven to ten days but more commonly occurs in fourteen days. For this to occur you need to train in the same conditions as expected on race day. You can mimic increased heat by wearing extra clothes. Fluid replacement should be done by drinking during runs and using the same drink on race day. Weight loss should be monitored during training in order to work out a fluid replacement plan based on sweat rate.
Adaptations to training or heat acclimatization has more benefits to performance than altitude training. Although most athletes pay more attention to altitude training. It leads to a number of changes in the body. The sweat rate is increased along with an earlier onset of sweating. The amount of sodium lost via sweating is reduced. The plasma volume increases and the heart rate is lower. The body core temperature is also lower and the perception of heat stress is decreased. The onset of fatigue is also delayed. All these changes prepare the body to be able to deal with heat stress more effectively.
On race day and before the race we anticipate salt loss and top up prior to the race. Pre-race hydration is also a must. 500 – 600 mls. is consumed in the 2 to 3 hours prior to the race with 300 mls. in the last 10 to 15 minutes. Knowledge of the WBGT level is necessary and NSAIDs except acetaminophen are to be avoided as these increase hyponatremia (low sodium levels).
During the race heat injury is minimized by fluid replacement using cool liquids with electrolyte and glucose replacement. Replacement volumes are individualized using the volumes worked out in training. Replacement should not exceed losses and the aim is to keep within 2% of body mass.
After the race, the aim should be to rehydrate early within 2 to 4 hours following the competition. Electrolytes and glucose should be replaced as this is essential in replenishing muscle glycogen stores. The amount of f luid to be replaced should be estimated based on the losses calculated when training.
Excessive heat stress can lead to the following disorders heat cramps, dehydration, heat exhaustion and heat stroke. We need to be able to recognize and treat heatstroke and heat exhaustion. The signs of these are dizziness, dryness of the mouth, reduced skin turgor and absence of sweating. There is also nausea, weakness, muscle cramps and an unsteady gait. The following also need to be looked for: vomiting, unresponsiveness, mental status changes, an increase in core body temperature to above 40.5 degrees centigrade, convulsions and involuntary bowel motions. If any of these are found then the runner should be evacuated to the hospital or clinic.
The following first aid measures can be taken for athletes suspected of having heat related disorders; place in shade, loosen or remove clothing, fan the athlete, cool by wet sponging, give fluids orally and intravenously.
The race organizers of the event or race should announce the current and predicted maximum temperatures as well as the WBGT category and risk profile. The location of aid stations should also be known. Fluids should be made available. Race monitors should be available and empowered to pull suspected heat sufferers from the race.
T he fluid stations should be about 2 to 3 Km apart and have a mixture of water and an electrolyte and carbohydrate mix available. There should be an adequate number of cups available which should be placed on tables for the athlete to take. A medical team inclusive of observers should be in place and there should be adequate communication between them.
If these measures and suggestions are observed heat related disorders should be significantly reduced.