Training and Competition in Warm Conditions
For those living in the UK, the summer is now upon us, and the prospect of training and / or competing in warm conditions is a (albeit remote) possibility. But should this make a difference to your training, and what considerations should be made before, during and after exercise to compensate for the environmental conditions?

It is widely accepted by Exercise Physiologists that exercise capacity, or the maximum amount of work an individual can complete at a particular intensity, is significantly reduced when performing in a warm environment. A recent laboratory-based study conducted at the University of Aberdeen asked trained individuals to exercise to exhaustion in an room maintained at four different temperatures, 4, 11, 21, and 31C (Galloway and Maughan, 1997). It is clear from the results of this study that the volunteers were capable of completing considerably more exercise at 11C than at the warmer temperatures. Surprisingly, exercise capacity was found to be significantly reduced at the relatively mild temperature of 21C, a temperature that is commonly experienced during the British summer time.

What causes this reduction in exercise capacity? Well at the moment this is still a matter of debate, but it is generally accepted that the decline in performance is caused through a combination of dehydration, additional cardiovascular strain, changes to the metabolism of carbohydrates and fats and potentially an acceleration of central nervous system fatigue. While it is currently unknown how these factors interact to limit exercise performance, a number of strategies can employed by you to reduce this loss.

While a diet high in carbohydrate is widely advocated for most runners, it may be particularly important when regularly training in a warm environment. The use of carbohydrates as a fuel for exercise has been found to be elevated in the heat, resulting in a quicker depletion of the body's limited stores of glycogen. This situation is known to contribute to the development of fatigue during endurance exercise in comfortable environmental conditions. While performance in the heat is generally not thought to be limited by the availability glycogen, it is important to ensure stores are adequately replenished following exercise, particularly if a number of training sessions are to be undertaken over a short period of time.

The major path for heat loss in a warm environment is through the evaporation of sweat from the skin's surface. Although sweat production is an effective means of dissipating heat, it occurs at the expense of the body's fluid and salt (sodium) stores, inevitably leading to dehydration. Without the consumption of drinks to replace the lost fluid and sodium, a reduction in blood volume occurs placing additional strain on the cardiovascular system. A reduction in the volumes of sweat produced can also occur, resulting in a dramatic rise in body temperature and in extreme cases the development of heat illness.

However, scientific research has shown that even when drinks are consumed, rarely do individuals consume adequate volumes of fluid to replace these losses (this has been termed voluntary dehydration). Therefore it is good practice to develop an effective drinking strategy, with particular emphasis on drinking before, during and after training. The American College of Sports Medicine (ACSM, 1996) has recently suggested that individuals should attempt to consume between 400 - 600ml of fluids 2 hours before starting exercise to help ensure that the body is well hydrated before commencing any activity.