Warm weather training can afford an athlete a welcome break from winter training. It provides an excellent opportunity to have a concentrated period of training with the added refreshment of getting some much needed winter sun. On the other hand, many sports events take place in summer months or warmer climates to which an athlete must adapt accordingly. Exercise during exposure to high temperatures brings about a significant change in the body’s response to exercise that must be accounted for in order to ensure the safety and maximise success of those who train and compete in warm weather.

Responses to exercise in heat

The most obvious response to unaccustomed high temperature exercise is an increase in sweat rates for a given exercise intensity. As the body’s core temperature rises, the hypothalamus signals to sweat glands to increase sweat rates in an effort to reduce the body’s temperature through the process of evaporation. The heat loss is through evaporation and is aided by dilation of blood vessels close to the skin surface, this allows the blood which has come from warmer core regions to release heat into the skin.

Exercising muscles require a constant supply of blood ensuring delivery of oxygen and fuels for energy and the removal of waste in order to allow the exercise intensity to be maintained. This can cause an internal competition for supply of blood between the exercising muscles requiring oxygen, and the requirement to dissipate heat through re-routing blood to the surface of the skin. The net effect of this is that cardiac output (a function of heart rate and heart stroke volume) is increased at a given exercise intensity relative to exercise in moderate temperature conditions. This elevation in heart rate results in maximal heart rate being reached at lower relative exercise intensities. In endurance events, as exercise continues, the volume of fluid leaving the body (through sweating and other routes of fluid loss) results in a reduction in blood volume, and this places further strain on maintenance of cardiac output. During intense warm weather exercise, the increased sweat rates reduce the transit time of fluid through the sweat duct. A lower fluid transit time reduces the retention of sodium, potassium and chloride ions that are lost in sweat. The loss of sodium, potassium and chloride can lead to a decrease in performance and has been linked to the onset of muscular cramp.

The net result of these actions is that perceived exercise effort is increased for a given intensity and that additional fluid and electrolytes are lost for a given training session.

Health risks with high temperature training

When exercising during high temperature a combination of external heat stress and internal heat generation can lead to heat cramps, heat exhaustion or heat stroke. Heat cramps are similar to the cramps most people are familiar with, except that instead of involving the small muscle groups, they affect the large muscle groups with severe and painful cramps. The losses of sodium are linked to their onset and are prevalent in heavy or ‘salty’ sweaters.

Heat exhaustion is the result of dehydration and results in an inability to regulate body temperature, its effect can be exacerbated during exercise as a consequence of the competition between the skin and muscles’ demand for blood. If heat exhaustion is untreated and becomes more advanced heat stroke may occur. Heat stroke is a very severe, life-threatening disorder that results from severe dehydration and the failure of the body to appropriately control its temperature. Heat stroke victims may cease to sweat in a last ditch effort to retain fluid, internal temperature rises dramatically above 40 °C. In addition, there is rapid heart rate and breathing rate and the victim will become severely confused.

Prevention of Heat illness

The most controllable factor in prevention of heat related illness is to reduce the intensity of exercise. If training must be completed in higher than normal temperatures, a reduction in exercise intensity should be implemented. Where intensity is paramount and must be maintained at high levels, the total volume of training must be reduced along with allowing greater recovery between efforts. This may necessitate shorter sessions.

Fluid considerations

Matching fluid losses with fluid consumption is important in temperate climates but essential in hot environments. During training sessions, a variety of fluids should be readily available for consumption. Fluid options should include drinks that are palatable in order to stimulate consumption, and should contain moderate sodium, chloride and magnesium levels to reverse electrolyte losses induced by sweating. Rest breaks that allow fluid consumption should be scheduled every 15-30mins during the exercise session. So that adequate rehydration can be implemented post-exercise, the athlete’s body weight should be monitored. Athletes should weigh themselves in as little clothing as possible immediately pre- and post-training. Weight lost during training is primarily due to sweating, by monitoring the amount of weight (fluid) lost to sweat we can calculate the required amount of fluid required to replace sweat fluid losses. A rule of thumb is to drink 1.5 L of fluid for every 1 kg of body weight lost during training. When rehydrating, formulations containing electrolytes and carbohydrate may be consumed to begin to refuel glycogen stores while replacing fluid. The combination of carbohydrate with electrolytes can increase the uptake of fluid, and this is particularly important when rapid uptake of fluid is required. The addition of sodium in fluids consumed during and post-exercise may also help to increase voluntary fluid consumption, as well as increasing the absorption of the fluids consumed.


Excessive clothing or garments which trap or retain heat should be avoided, and loose fitting clothing that allows air flow around the body while maintaining sun cover should be worn. Items that hold moisture, such as cotton, should be avoided, and should be replaced with polyester-based clothing where possible. During prolonged exercise, the amounts of clothing worn should be reduced to allow heat to dissipate and to avoid clothing-mediated temperature increases. However protection from direct sun exposure with sun screen must become a priority when clothing is being removed.

Acclimatisation to a warm environment

The adaptations made in response to exercise in warm weather can be seen during regular training in warm conditions and are known heat acclimation or acclimatisation. The changes begin immediately and continue for approximately 10-14 days as the body improves its ability to manage exercise-induced heat production through more efficient dissipation. In a study of the time course of heat acclimatisation, over a twelve day period, an exercise group were show to have a continually reduced heart rate and core temperature, and an increased sweat rate in response to a set daily exercise session. After acclimatisation, the training group was shown to have a reduced heart rate and core temperature along with an extended time to fatigue in comparison to the non-acclimatised pre-test.

Acclimatisation will depend on the environmental conditions (heat, humidity and wind), duration and individual intensity of training sessions as well as the fitness of the athletes. However, it appears that one week is sufficient to gain a significant, if not complete, acclimatisation effect.

To affect acclimatisation athletes should train as normal but training should be adjusted to minimise the effect of heat on the athlete. Intensity of training should be reduced as described above during the initial stages (3-7 days) of acclimatisation.


Warm weather training can give a welcome change to winter training for athletes. Training in warmer climates will require a period of acclimatisation during which it is essential that the athlete’s timing, volume and intensity of training are adjusted to ensure that the athlete is not over-stressed by the training load. The body weight of the athlete must be measured to monitor fluid loss. Fluid losses should be offset by consuming fluids frequently during training and should be replace post training. Drinks used to replace lost fluids should have electrolytes and may contain some carbohydrate. Clothing should be light, allow air flow around the body and where possible assist in protecting skin from direct sunlight. Polyester clothing is superior to cotton as it does not absorb the same quantity of sweat against your body allowing more effective sweating.

In brief

Exercise in the heat causes

  • Increases sweat rate and fluid loss
  • Increases electrolyte loss in sweat
  • Increases heart rate for a given work intensity
  • Competition for blood flow between working muscles and the skin
  • Reduces work capacity if core dehydration or elevated core temperature ensues
  • May cause heat cramps, heat exhaustion or heat stroke

Over heating can be avoided by

  • Avoiding training during peak temperature times
  • Schedule training for early morning/dusk
  • Scheduling regular fluid breaks every 15-30 min
  • Remove unnecessary clothing that may trap heat
  • Ensure clothing allows air flow and allows direct sun exposure protection
  • Adapting intensity and volume of training during early acclimatisation (3-7 days)


  • Immediate onset
  • Up to 10-14 day duration necessary for full acclimatisation
  • Fitter athletes require fewer heat training exposures to acclimatise

Hydration is essential

  • Assess body weight before and after training to assess fluid loss
  • Have fluids available during exercise
  • Schedule hydration breaks regularly every 15-30 mins
  • After exercise, consume 1.5 L of fluid for every 1 kg of bodyweight lost during exercise
  • Fluids containing moderate carbohydrate and sodium can be consumed to assist fuel and fluid replacement