A model for heat training ― The Davies heat model

by Chris Davies

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    Chris Davies has lived and trained as a national class distance runner in the tropical north of Australia. While based in North Queensland he completed postgraduate studies in heat acclimatisation in elite athletes. Davies has spoken at a number of conferences on the subject. He was a National Technical Official for Modern Pentathlon at the Sydney 2000 Olympic Games.
    Chris Davies is presently undertaking a PhD in sports law and is a tutor in law at the James Cook University. He has also established a sports consultancy business, "Olympic Pursuits", specialising in sports law and sports science.



    Heat has proven to be a critical factor in many Olympic Games and World Championships, particularly in the longer endurance events. Sports scientists have traditionally viewed heat acclimatisation as purely a physiological question. The author, however, argues that studying the physiology is but one third of the heat equation, and suggests that if athletes adapt the correct behaviour patterns by moving to the right place at the right time, they, in effect, do not have to heat acclimatize. The Davies Heat Model is designed to help coaches and athletes in this regard. The Davies Heat Model also introduces the third concept of heat acclimatisation; namely, climatology, which also needs to be carefully studied if elite athletes are to be properly prepared for the heat.

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General Introduction

    Over the past twenty years, events such as the Olympic Games and IAAF World Championships have had, invariably, one thing in common: warm to hot, and, often, humid conditions. It is arguable that in events like the marathon the results have been determined just as much by the runners' ability to handle the prevailing conditions as by natural athletic ability and fitness. Other major sporting events, such as World Cup Soccer, also experience these types of conditions, as shown in Italia '90, USA '94, and what will be shortly encountered in Japan and South Korea in 2002.
    It is a proven physiological fact that heat does have an effect on performance. However, as a runner like Carlos Lopes showed in the 1984 Los Angeles Olympic Men's Marathon, someone well acclimatized to the prevailing conditions of 27 C can perform exceptionally well, as his still existing Olympic record of 2:09:21 clearly indicates. The same race also showed that it is possible for an Irishman and an Englishman to perform far better than runners from much warmer countries, as long as they are prepared to undertake a suitable and appropriate heat acclimatisation programme. This particular marathon race clearly illustrated that a poorly conceived and poorly executed heat acclimatisation programme will result in a far worse performance than when no acclimatisation programme is undertaken at all.
    The purpose of this paper is to present a model for heat training, together with strategies to help reduce the heat's potential depleting effects on performance. Originally designed prior to the 1988 Seoul Olympic Games, it is based on an analysis of the 1984 Olympic Marathons, as well as the vast amount of literature written on the broad topic of heat stress and exercise. It is suggested that the numerous warm to hot weather major championship marathons since 1984 have confirmed the accuracy of the model's basic principles.
    For the purpose of clarity, this paper is divided into four parts. In Part I, a general description of the Davies Heat Model is given, along with a thorough outline of Davies' guiding principles (or 'rules') for heat acclimatisation. Part II deals with practical application of the rules of the Davies Heat Model to training in the natural environment. In Part III, a short advisory is offered on the use of artificial means; namely, on the use of heat chambers, to assist athletes in their adaptation to heat. Finally, in Part IV, the need for a careful climatological study of the competition location is discussed, so that athletes and coaches can make a realistic assessment as to whether heat acclimatisation is even necessary.

Part I. The Davies heat model: general description
    A key concept underlying the Davies Heat Model is the contention that when heat acclimatisation is not done properly athletes run the risk of depleting themselves to such an extent that they will perform at a level far worse than if they had attempted no heat acclimatisation programme whatsoever. The description of the heat acclimatisation process given immediately below offers the physiological rationale for the rules of acclimatisation, which follow.

The Heat Acclimatisation Process
    While most text books usually refer to the 10-14 day period as the time span needed for heat acclimatisation, they fail to mention that trying to maintain heavy training while undergoing these quite drastic physiological changes has led to athletes depleting themselves and, as a consequence, showing the classical over training symptoms of sudden and dramatic decline in performance.
    Understanding how the body adapts to heat enhances the understanding of how this depletion can occur. The heat acclimatisation process is, thus, explained below and illustrated in Figure 1.
    The stages of heat acclimatisation can be defined as follows:

Stage 1. The 48 Hour Window: This stage spans a short two- to, perhaps, four-day period of exposure to a warmer climate. It is the period of time before the body begins to undergo the heat acclimation-acclimatisation process. The body is left un-acclimatized, but just as importantly, un-depleted, having not ventured into the risk-prone Heat Acclimation Stage (Stage 2). where complications from a visit with the "Heat Depletion Zone" could be experienced.

Stage 2.  Heat Acclimation and the Heat Depletion Zone (4 to 14 days): What most textbooks describe as the four to fourteen day period needed for heat acclimatisation, the author would define as "heat acclimation". [Note: see below for a discussion of the difference between heat acclimation and heat acclimatisation.] The continuation of heavy training during the acclimation stage, where the body is undergoing major physiological changes in response to the change in climate, could lead to a situation where the body will become depleted a circumstance which the author has labelled, the "Heat Depletion Zone". As will be discussed in more detail below, restricting climatic change to less than 8 C means that the physiological changes will be less drastic, thus enabling an athlete to continue training at a normal level without the risk of entering the Heat Depletion Zone.

Stage 3. Heat Acclimatisation (Short Term) (2 weeks to 3 months): It is in the period from two weeks to three months that the most significant heat acclimatisation processes take place, and three months at a suitable temperature is an ideal time period for heat acclimatisation. It is important to note, however, that an athlete needs to be sufficiently acclimated-acclimatized at the beginning of this three-month period in order to be able to train properly throughout that period.

Stage 4. Heat Acclimatisation (Long Term) (3 months to 2 years): This stage is identified in recognition of the fact that, while the most significant part of the acclimatisation process takes place within the initial three month period, subtle physiological changes to hot conditions such as those encountered in the tropics continue for a period of up to two years. Skin wetness, for instance, continues to suppress the sweat rate, thereby conserving water, while skin blood flow also continues to improve during this period.

Stage 5. Genetic Adaptation: Finally, built into the model shown in Figure 1 is the recognition that genetic selection can automatically provide some acclimatisation to heat. For example, the literature indicates that people of Negroid descent tend to be genetically adapted to heat. But the results of major championship marathons also indicate that Caucasian bodies can fully adapt to warm, humid conditions if they spend sufficient time in the right environment.


Heat Acclimation versus Heat Acclimatisation
    While most textbooks define 'heat acclimation' as what takes place in heat chambers and 'heat acclimatization' as the process that occurs in the natural environment (Wilmore and Costill, 1999). the author defines the terms as follows:
    Heat Acclimation: The physiological changes that occur in the four to fourteen day period following exposure to heat.
    Heat Acclimatisation: The physiological response to heat that occurs after the end of the initial two-week period and which may continue for up to two years.
    Thus, the author distinguishes between what takes place in the four to fourteen day period (Stage 2) and what takes place in the two-week to three-month period (Stage 3). The reason for such a distinction is to emphasize the difference between the period where the body undergoes the most dramatic physiological changes needed to combat the heat. and the much longer time period where the body continues to undergo the  more subtle changes that are still required for optimum athletic performance in the heat.
It is important to note that it is only after going through heat acclimation that an athlete is in a position to handle a heat acclimatisation programme. For many passive and/or indoor sports, a heat acclimation programme is all that is required, as indicated in Part II of this series.

Classification of Temperature Zones
Despite the vast array of literature available on the subject, there is no mention of the fact that the body can handle a certain change in temperature without it having to resort to major physiological adjustments. The Davies Heat Model suggests that th is temperature difference is around 8 C. Thus, it is safe for an athlete to change environments with a temperature difference of less than 8 C, and still safely maintain a heavy training load. As can be seen on the chart in Figure 2 of the Davies Heat Model, temperatures in relation to the heat can be divided into seven zones:

1. The 'Too Cold Zone 1' (anything below 15 C): At temperatures below 15 C even the use of heat chambers is risky because of the temperature differences between the environment and the chamber. At these temperatures the body is essentially de-acclimatized to the heat, and is adapting to the cold. It is a zone that should be avoided by athletes seeking heat acclimatisation.

2. The 'Too Cold Zone 2' (15-18 C): Temperatures between 15-18 C, while not suitable for heat acclimatisation in itself, do at least allow athletes to use heat chambers set at a "safe" temperature range of 18-23 C. In this situation, the chamber temperature can even be set as high as 25 C, particularly if the athlete makes other behavioral adaptations, like wearing extra clothing during the day, staying out of the cold night air and training as much as possible in the warmest part of the day. The other benefit of this zone is that it can be used by those in Ideal Zone 1 or Ideal Zone 2 (see below) for two-week periods for competition purposes.

3. The 'Thermoneutral Zone' (19-22 C): The Thermoneutral Zone is the minimum temperature range at which physiological adaptation to the heat remains. Below this, if exposed to the cold for a period of more than 2-3 weeks, the body begins to acclimatize to the cold. Athletes who have been training in the Ideal Zones can safely return to the Thermoneutral Zone without the threat of losing their heat acclimatisation, thus enabling the use of a Thermoneutral Zone for extended periods of time. If an athlete is coming from a colder zone, then the Thermoneutral Zone is where heat acclimatisation begins.

4. The 'Ideal Zone 1' (23-26 C)

5. The 'Ideal Zone 2' (27-30 C): The ideal temperature range is somewhere between 23 C and 30 C, depending on the anticipated competition temperature. Whether it is Ideal Zone 1 or Ideal Zone 2 that is selected for the training environment will depend on the circumstances.

6. The 'Six Week Zone' (31-34 C): While it is possible to train in the 31-34 C range, it is suggested that training periods of longer than six weeks should be avoided because of the danger of accumulated fatigue arising from continuous training in such conditions. It is also suggested that this zone should not be used in the months immediately preceding a major event unless the athlete or athletes concerned have had previous experience training in such conditions.

7. The Too Hot Zone' (anything above 34 C): Spending extended periods of time in places where the temperature is above 34 C should be avoided. Contingency plans should be implemented to ensure the avoidance of heat wave conditions in an area where otherwise ideal heat acclimatisation would take. place.


Rules for Heat Acclimatization
    The above identification of temperature zones and accompanying discussion alludes to guiding principles that pertain to heat acclimatization programmes. The following rules are the ones by which the Davies Heat Model operates:

1. An athlete should never move more than two temperature zones at a time, that is, more than 8 C. Exception: It would be acceptable to move three zones at a time at the lowest end (Zones 1 to 3).

2. For any Category 1A event (defined in Part II of this series), such as the marathon, a heat acclimatisation programme needs to be undertaken when the event conditions are expected to be 20 C or greater. For other sports, it is several degrees higher, at around 22-23c.

3. Training is best done in the temperature zone that best matches the anticipated competition temperature, with the following considerations:

    (a) If the competition is going to be in the Thermoneutral Zone, then training in Ideal Zone 1 may be the best option, all other factors making it practical.

    (b) If it is anticipated that competition temperature will be above 27 C, then training in the zone below the anticipated conditions may be the best option to help ensure under training in relation to the heat.

4. Never train in conditions above 30 C for more than six continuous weeks, because of the risk of accumulated fatigue. If an acclimatization programme breaks Rule 1, then the athlete's training must be reduced by approximately 50% in both quantity and quality to offset heat-induced depletion.

Humidity Factor
    The Davies Heat Model is set at a Relative Humidity (RH) of 60-65%, a level that is significant but not excessive. If an athlete should move to a place under 65% RH, the model works as it is. However, if the humidity of the place where the athlete is going is greater than 65% RH, then the model needs to be adjusted by approximately 1 C for every 5% RH. That is, if an athlete moves from a region where the humidity is below 65% to another where the RH is around 80%, then acceptable temperature change would have to be restricted to a change of 5 C as opposed to 8 C.

    The uniqueness of the Davies Heat Model, as explained above, lies in its identification of ways and means by which the athlete might become vulnerable to physiological depletion during the heat acclimatisation process. In delineating rules by which adaptation to heat can be safely accomplished, Davies offers information of great potential usefulness for anyone who might be faced with the task of preparing an athlete for a major competition where heat poses a potentially important factor in the performance outcome. In Part II, Davies illustrates how these rules can be implemented in a practical way, taking into account the nature of the sport and the anticipated conditions.

Part II. The Davies Heat Model: Strategies For Heat Acclimatisation In The Natural Environment
The basic presumption behind the Davies Heat Model is that the body can handle certain changes in temperature without having to undergo major physiological changes. It is these major physiological changes, combined with the heavy training needed for an event, such as the marathon, that can seriously deplete the body. In a sense, the body 'over-acclimatizes', leading to what amounts to an over-training scenario, marked by the classic over-training trademarks of a dramatic and sudden loss of training form and competition performance.
    Here, in Part II of this series, 'rules of engagement' are established and practical guidelines are given to assist coaches and athletes in the application of the Davies Heat Model to heat adaptation in the natural environment. After a brief review of the general rules, event-specific strategies for acclimatisation are offered.

The Do's and Don'ts of heat acclimatiation
The Do's

●    Train in a Zone below the anticipated or most likely competition temperature. That is, err on the side of under-training rather than over-training in relation to the heat.

    If training has to be curtailed because of other needs, like competition, then compromise in the direction of a lower temperature rather than spending a shorter time at a higher temperature and running the risk of entering the Heat Depletion Zone.

    Avoid, if possible, having to acclimatize, except in the safe, natural springtime situation, or at a time when very light training is a part of the training regime.

    In the final few weeks before a major event only train in a temperature zone you know you can handle.

    For extensive sports think of heat acclimatisation in terms of months, not days or even weeks.

The Don'ts

●    Don't move more than two heat zones, that is, 8 C. and, at the same time, try to maintain a full and heavy training schedule.

●    Don't train in the final few weeks before a major championship in a temperature or humidity level you have never experienced before.

●    If an athlete wishes to remain acclimatized to a particular heat zone then this person should never move more than 8 C away from it for more than two to three weeks, as re-acclimatisation will be required.

    It is important to remember that heat acclimatisation is something one does properly or not at all. And if there is a secret to heat acclimatisation, it is never having to acclimatize, except naturally during springtime.

Categories and strategies for heat acclimatisation
    By using the Davies Heat Model a number of different strategies can be implemented, thus allowing the flexibility needed to take into account other necessary considerations like the need for competition. Table 1 offers an over-view of heat acclimatisation strategies by event category, as suggested by Davies. A detailed description of each of these parameters is given below.


Event Categories
    Although based on data from marathon races, the Davies Heat Model is nevertheless suitable for all the major sports; the level of acclimatisation and, hence, the amount of exposure to the heat that is required being dependent on three factors:
    1. Length of the event
    2. Level of physical exertion required for the event, and
    3. Location of the event: indoor versus outdoor.

    Before deciding what strategies are best implemented for each event in Athletics, it is first necessary to classify the various events into specific categories depending upon the three factors mentioned above. Using such criteria the following categories can be established:

Category 1A:

    Highly strenuous, extensive outdoor events. Example: Marathon

Category 1B:

    Strenuous, extensive outdoor events. Examples: 10000m, 20k Walk, 50km Walk.

Category 2A:

    Strenuous, reasonably extensive outdoor events that are either less extensive that Category 1A or have built-in breaks. Examples: 5000m, 3000m Steeplechase, 10km Walk, Decathlon, Heptathlon

Category 2B:

    As for Category 2A. but less strenuous/extensive. Examples: 800m, 1500m.

Category 3:

    Non-strenuous outdoor events, or strenuous indoor events. Examples: 100m, 200m, 400m, Relays, Field Events.

Category 4:

    Non-strenuous, indoor events. Thus, for outdoor track and field competitions the events will fall into Categories 1 to 3, while the timing of the major indoor meets usually means that heat acclimatisation is not an issue.

Heat Acclimatisation Strategies
    Strategy 1: Base yourself in a hot climate with an all year round temperature range of 19-33 C for a period of two years.

    Strategy 2: Move to a suitable climate three to six months prior to the event, incorporating some easy weeks into the training programme if breaching the rules of the Davies Heat Model.

    Strategy 3: Move to a suitable climate three months before the competition, but at the same time make sure there is no chance of depleting the body.

    Strategy 4: Move to the venue less than three months, but more than two weeks before the event, again adjusting the training to ensure no depletion takes place.

    Strategy 5: Arrive two weeks or less before the event and heat acclimate under a reduced training load.

    Strategy 6: Make use of the 48-hour window and arrive a day or two before the event. The nature of the actual event, and other requirements, such as the need to qualify for the event, or the need for pre-event competition, will all influence what strategy will be adopted.

Synthesis: Heat Acclimatisation Strategy by Event Category
    For each of the various event categories, the following heat acclimatisation programmes could be safely implemented (also summarized in Table 1):

Category 1 A:
    1. Ideal: Strategy 1
    2. Highly recommended: Strategy 2 and 3.

    3. Suitable: Strategy 6
    4. Avoid: Strategies 4 and 5

Category 1 B:
    1. Not needed: Strategy 1

    2. Ideal: Strategy 2 and 3

    3. Suitable: Strategy 6
    4. Avoid: Strategy 4 and 5

Category 2A/2B:
1. Not needed: Strategy 1
    2. Not practical: Strategy 2
    3. Ideal: Strategy 3
    4. Highly recommended: Strategy 4

    5. Suitable: Strategy 5 and 6

Category 3:
    1. Not needed: Strategy 1 and 2
    2. Ideal or Suitable: Strategy 3,4,5 and 6

Category 4:
    1. Not needed: Strategies 1,2 and 3
    2. Ideal or Suitable: Strategy 4, 5 and 6.

    What is clearly illustrated here in Part II of the Davies Heat Model is that what may be ideal or suitable for one event, can either be unsuitable, impractical or simply not needed in another. Not only does a heat acclimatisation programme, therefore, have to be tailored, specifically, to the anticipated ambient conditions, it also has to be tailored to the specific needs of the individual athlete, for a particular event.

Part III. The Davies Heat Model: Practical guidelines for the use of Heat chambers
    In Part II of this series, the guidelines as specified by the Davies Heat Model dealt with the way in which the natural environment can be used for both heat acclimation and heat acclimatisation. It is possible, however, that such a programme may be inconvenient for a team or athlete. In this case, heat chambers do have a role to play in heat acclimation and even heat acclimatisation. It is the author's view, however, that heat chambers are frequently used incorrectly, the most common mistake being the selection of excessively high temperatures in the midst of a cold winter. The body is, thus, exposed to quite drastic temperature changes on a daily basis.

Heat chambers can be best used in the following situations:
    1. In the summer to help athletes prepare for conditions either a little hotter or a little more humid than their hometown.
    2. In the autumn to prolong the natural summer acclimatisation process, delaying the need to move to a warmer climate.
    3. In the spring to enhance and quicken the natural heat acclimation and acclimatisation processes.
    4. In places with a mild winter for example, in places where the temperature remains around 20 C to provide heat acclimatisation without requiring an athlete to leave home.

    While the Davies Heat Model is designed primarily for application to the natural environment, its principles are equally applicable to the use of heat chambers according to the following guidelines:
    1. Don't use a heat chamber in an active way where the difference between the outside temperature and that being used in the heat chamber is greater than 8 C, as the body will have difficulty coping with the changes in temperatures and the potentially strenuous work load.
    2. Using heat chambers at 30 C is fine if an athlete lives in a climate of 22-23 C. But if the outside temperature is only 17-18 C, then the athlete would be better off using the heat chamber at only 25-26 C. In other words, keep the temperature difference to less than 8 C.
    3. It is not advisable to actively use a heat chamber where the climate is less than 15 C. Migration to a warmer climate is really the only viable option.
    4. This advice is reserved for what can be described as active use of heat chambers; that is, using them for actual training sessions. Spending passive time in the chamber by doing little more than just sitting around in the chamber, is not likely to cause any real problems and may provide some heat benefits.

    When using an artificial environment, such as the heat chamber, for adaptation to anticipated warm-weather competition conditions, it is tempting to boost the temperature immediately to levels resembling the tropics. The author strongly advises athletes and coaches to curb this temptation, especially if the natural environment that surrounds them involves temperatures below 20 C.

Part IV. The Davies Heat Model: Climatological considerations
    The Davies Heat Model is unique in that it takes into consideration the fact that exercise physiology is only a third of the heat acclimatisation equation. Major behavioral patterns, such as the movement of athletes from one climate to another, and climatological factors must also be understood in order to complete the picture.
    Behavioral factors, such as putting on or taking off clothing, are far more important in humans than the physical capabilities of withstanding environment extremes. In the case of elite athletes, the behavioral pattern of moving to the right place at the right time is a highly critical behavioral factor in heat acclimatisation. As the Davies Heat Model indicates, getting these behavioral patterns right can effectively eliminate the physiological side of the equation. What remains, then, is one uncontrollable aspect of the equation: the weather.
    A study of the average temperatures of particular locations at particular times of the year is relatively easy and offers some guidance as to what places might suitably mimic anticipated competition conditions. However, average temperatures are just that: averages. Sometimes the temperature can be significantly higher than normal. What will, in normal years, constitute a perfect heat training regime, may, in some exceptionally hot years, prove too hot for safe heat training, as the Japanese marathon runners found to their detriment prior to their 1984 Olympic campaign. Conversely, the temperature in a given year at a particular location may be well below average, to the extent that it is insufficient to provide the required heat acclimatisation.
    Predicting the actual race conditions can also be difficult. The following question might be posed, for example: Which city has the record for the hottest Olympic marathon? Rome? Tokyo? Los Angeles? Barcelona? Interestingly, it was Stockholm in 1912. What are the odds of a 39 C day occurring on a particular day in Stockholm? Quite long, perhaps, but eighty-three years later the nearby city of Gothenburg also had unexpectedly hot conditions when it hosted the 1995 World Athletics Championships. London, too, produced a warm, humid 25 C temperature for its 1908 Olympic marathon. And it is certainly possible that similar temperatures could prevail during London's 2005 World Championships.
    When planning ahead, what first needs to be established is the likelihood of warm conditions prevailing at a given venue. For places like Athens it is essentially 100%, since Greece has virtually no cool days during its long summer. In some ways, this is the easiest temperature regime to prepare for, as you can predict exactly what to expect. Cities in places like Northern Europe, on the other hand, are far trickier. On an average summer's day they are not places where heat acclimatisation is required. Yet they are capable of having some very hot summers, and some exceptionally hot summer days in what is otherwise a mild spell of weather.
    A venue like Sydney, meanwhile, being in the southern hemisphere, has an early spring and an average temperature of around 20 C. Yet, there is an approximately one in six chance of temperatures above 25 C degrees occurring any given day in the period when the Olympic Games were held (or, in certain years, weeks of such temperatures, as was the case for 2000). While the men's marathon had relatively mild weather on the last day of the Games, the runners were one day away from having to compete in 26 C and two days away from having to deal with the 35 C temperatures that the 50km walkers had to cope with.
    Thus, it is only a careful study of the temperature recordings over the preceding decades that can give an indication of the chances of a particular temperature occurring. It is from this information that an athlete or coach can make an informed assessment of whether, firstly, a heat acclimatisation programme is actually needed, and, secondly, a certain location would be suitable for such a training programme. For a venue like London, or Sydney in September, the odds probably indicate that no acclimatisation is needed. But, then, is it worth leaving four years of hard effort in the laps of the weather gods?
    Establishing the exact weather patterns in the location chosen for the heat acclimatisation programme is equally important. The average temperature may be perfect, but what if it is under the average? Will it still be suitable for the anticipated conditions? And if it is above average, will it be too hot for a safe acclimatisation programme? In both situations a contingency plan is advisable. When deciding on a place the possible variations need to be considered as well as the average temperatures. Sometimes a particular location may, at first glance, not appear as suitable as another. On closer examination, however, the known temperature variations may mean the former is the safer option, and, therefore, the better option.

General discussion
    A key concept of the Davies Heat Model is the notion that, especially for events that are both strenuous and extensive, a far greater time span is needed for full heat acclimatisation for optimum athletic performance than the textbook 7-14 days (Wilmore and Costill, 1999). Indeed, the very observance of this two-week acclimatisation period has probably been the underlying cause of numerous failures of high profile athletes when confronted by warm to hot conditions.
    Dr. Dick Telford, Rob de Castella's scientific adviser in Los Angeles, suggested that de Castella had been fully acclimatized to the heat there, despite only a month's exposure to the heat, and put the blame on his failure down to his greater body size (Telford, 1985). Not once in his article did he mention the fact that the three medal winners had all been training for three months in conditions similar to those experienced in Los Angeles, and that this may just have had something to do with their subsequent success. The gold medal performance of Italy's big man, Gelindo Bordin, in the warmth of Seoul four years later would appear to dispel Telford's greater body size theory.
    While reporting on their athlete's performance, Salazer's scientific advisers made the pertinent comment that marathon running and laboratory-based running are two different things (Armstrong, et. aI., 1986). Indeed, both de Castella's and Salazer's performances at the Los Angeles Olympics in 1984 prove that exclusive reliance on laboratory or even field-based physiological testing can be misleading, as these tests do not necessarily take into account the environmental demands that the body might face on the day of competition.
    While the Davies Heat Model is based on a thorough understanding of the relevant literature on the subject, it is also one that incorporates a fresh approach to the problem; namely, it incorporates into its explanation observed patterns of training behaviours and performances at major championship marathons. It also differs from most other studies in relation to the question of heat acclimatisation, in that it incorporates deductive reasoning rather than the inductive approach that, invariably, prevails in exercise physiology. Therefore it can be applied to all sports and all ranges of temperature, rather than being limited to specific temperature ranges and specific sports.
    The Davies Heat Model is based on the marathon, placing this event at the apex of heat acclimatisation. What can be learned from this event is, then, watered down for less strenuous and/or less extensive sports. To take the opposite approach, from less strenuous and/or extensive sports to ones more strenuous and/or extensive, is less reliable and, actually, can lead to faulty programming.
    How the body adapts to the heat has been well documented for decades, with the number of studies in the broad area of heat stress and exercise now numbering near the 400 mark. Interestingly, not one of these studies attempts to offer elite athletes the practical guidelines they require. It is suggested that this is because they do not take into consideration the major behavioral patterns that are needed: (a) to avoid the need to heat acclimatize and/or (b) to adjust the training so as not to deplete the body in the heat.

    Heat is a constant companion for athletes competing in major championships. An assessment of marathon races in these championships suggests that heat acclimatisation is something that ought to be done properly, or not at all. It also suggests that an athlete who has carried out a proper heat acclimatisation programme for a strenuous and extensive event will always beat a non-acclimatized athlete, all other factors being equal. As the likes of Charlie Spedding showed in Los Angeles (1984), and American Steve Spence showed at the World Championships in Athletics Tokyo (1991), well-acclimatized athletes can beat even superior runners who have not properly prepared for the heat.
    It is hoped that what this paper has achieved is the provision of heat acclimatisation guidelines for athletes and coaches. The concepts offered in this document should be useful in helping such individuals to decide if a heat acclimatisation programme is required and, if so, what should constitute a suitable programme. And, perhaps for the exercise physiologist, it will provide food for thought regarding theories of heat acclimatisation and how these fit with the harsh reality of elite competition.


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