Being cooked in the heat chamber

Many hours in the heat
chamber at 35 degrees simulating Hawaii
conditions

The heat
Heat is one of the greatest challenges for the human body. Fortunately, humans are quite remarkable in their ability to adapt to extreme environments and people survive in very cold and very hot environments. However heat remains one of the major stresses for our body. We function well if our bodies are at 37oC but if we heat them up to 41oC they will start to fall apart. Heat has a major impact also on physical performance.

When we exercise we burn fuels to generate ATP which is the ultimate fuel for muscle contraction. However, not all of that energy we expend is used for muscle contraction. In fact only about 20% of the energy is used for contraction and the remaining 80% is wasted as heat. This heat produced warms up the muscle and cooling mechanisms must make sure that the muscle does not get too hot. When the proteins of which our muscle and in fact our entire body is built are exposed to temperatures above 41oC they start to denature (break down). This is not dissimilar from what happens with a car engine. Petrol powers the engine but heat is produced at the same time. A cooling system (i.e. radiator) is in place to make sure the engine does not overheat. Without the appropriate cooling systems humans would overheat very rapidly during exercise, even when the environmental condition would be cool. The body gets rid of heat via various mechanisms, one of them being the evaporation of sweat from the skin, and another one being convection. Convection means that heat from the body is directly transferred to the environment (the air surrounding the body). Of course when the temperature of the air is close to or even exceeds body temperatures this methods of cooling is ineffective.

Physical performance is seriously reduced even with relatively small increases in environmental temperature and even if a person is fully acclimatised to the heat. When unprepared however, the effects of heat can be very severe and even fatal. Typical temperatures in Hawaii are 29 degrees and 65% humidity, and such conditions are a serious challenge to the body. I was well aware of the importance of adapting to those conditions. Unfortunately around October it is getting pretty cold in England and there is no chance to acclimatise in the country. It is also the time that work is getting even busier and therefore I had no opportunity to go abroad for hot weather training. So I had to talk to experts and find out how to best prepare for the conditions given the constraints I had.

Repeated exposures to the heat result in physiological adaptations that reduce the impact of the environmental conditions on exercise performance. One of the adaptations to repeated exposures to exercise in the heat is a reduction in the pre-exercise body temperature. A normal body core temperature of 37oC may drop to 36.5oC after repeated heat exposure. Studies revealed that the rise in core temperature was not changed over successive days of exercise in the heat, but exercise capacity was increased because of the longer time to reach a critically high core temperature.

The adaptation to heat that occurs is dependent on the amount of heat strain to which the individual is exposed. To obtain an adaptation to hot humid conditions it is important to: (1) raise body temperature and (2) induce a sweat response. Adaptation, therefore, depends largely on the intensity and duration of exercise and on the environmental conditions, and there is clearly an optimum set of conditions for the most effective acclimatization. Some adaptation is seen within the first few days of exposure to exercise in the heat, and even a few sessions of exercise in the heat are beneficial. Adaptation is more or less complete for most individuals within about 7–14 days, so there may be no advantage in living for prolonged periods in a hot climate. It is equally clear that regular endurance training in temperate conditions confers some protection, with an expansion of the plasma volume being a significant adaptation that is common to both of these stresses.
Trained individuals are therefore already partially adapted, but it has to be admitted that it is not known how complete this process is for highly trained athletes. The endurance athlete who trains wearing extra clothing to induce sweating even in a cool climate will also show some degree of heat acclimation, but this process can be further enhanced by a period of training in the heat.

There are two ways of acclimatizing for competitions in the heat, and various combinations of these two approaches are also possible. One is to live and train in a climate similar to that expected at the competition venue: this is referred to as acclimatization. The other approach is to live at home and adapt by training in an artificial climate: this is referred to as acclimation. There are positive and negative aspects to both approaches. Because exercise capacity is reduced so much in the heat, training intensity and volume must be reduced for at least the first few days of the acclimatization process. This effect may be minimized if the athlete lives at home and is exposed to heat only during training, or during one of two daily training sessions, allowing some quality training to be continued in the other session. If two training sessions per day are carried out, whether at home or in a hot weather camp, it seems sensible for the quality session to be done first, with the heat acclimatization session coming later in the day. The quality training session should be outdoors if at home, or in the early morning while it is still cool if at a hot weather venue.

The weather is notoriously unpredictable, and the acclimatization venue selected may not provide suitable conditions for optimum acclimatization, whereas these can easily be simulated at home. If the heat acclimatization training is one of two sessions per day, the athlete is generally happier to adopt a less drastic regimen: the heat training can be gradually phased in, beginning with short (perhaps 30–60 min) sessions at low intensity without compromising the overall quality of training. It is not necessary to train every day in the heat, but no more than 2–3 days should elapse between exposures: it has been shown that exercising in the heat every third day for 30 days resulted in the same degree of acclimatization as exercising every day for 10 days.

This is because it takes time to reverse the adaptations to heat; for individuals who are completely acclimatized, some of the improved responses are still present after as long as 21 days in a cool climate. Acclimation at home means that the athlete can introduce the heat acclimation sessions gradually while continuing with normal training, and is not trying to cope with the effects of heat, jet lag, travel fatigue and other travel-related problems at the same time.
A disadvantage of training in a hot room may be that the exercise inevitably depends on the facilities available and probably consists of cycle ergometer exercise, treadmill running, skipping or circuit training. From the point of view of acclimatization to the heat, the type of exercise is not important: what does matter is that a period of prolonged (60–100 min), moderately strenuous exercise is carried out in hot conditions. The intention is to raise body temperature and to stimulate sweating, as these are the factors that promote adaptation. There is evidence that full acclimatization is most effectively achieved when the duration of exercise in the heat is about 100 min, and that there is no advantage in spending longer periods than this exposed to heat.
Intermittent exercise is likely to be as effective as continuous exercise, and is likely to be more acceptable to sprinters and to team games players: the total exposure time, including short breaks, should again be 100 min for the most effective adaptation. There is some evidence, however, to suggest that exercise at higher intensities for shorter periods of time may be equally effective in bringing about beneficial adaptations, and that even 30 min per day at an intensity equal to about 75% of maximal oxygen uptake (VO2max) was as effective as 60 min at 50% of VO2max. After exercise in the heat, the athlete should aim to reduce body temperature rather quickly by seeking shade or an air-conditioned environment to cool down and hasten the recovery process.
If acclimatization is to be realized at a hot weather camp, advance information on local weather patterns is essential to allow forward planning. The training programme may have to be modified to take account of the prevailing conditions, whether these are more or less stressful than the average. The time scale for such a programme should be sufficient to allow for a few (at least 3–4, but perhaps as many as 5–10) days of reduced training upon arrival: both total training volume and the amount of training at high intensity should be reduced, the extent of the reduction depending on the individual response. Normal training can then be re-established for a few days while the acclimatization process continues and before tapering for competition begins: the vital ‘quality training’ should continue, with enhanced periods of rest and recovery, over the final week before competition. Recovery after or between
exercise sessions will be faster and more complete if it is possible to find a cool shady place for this work.