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International SportMed Journal
Environmental considerations for athletic performance at the 2008 Beijing Olympic Games *Dr Jill Borresen, BSc(Med)(Hons), PhD (Exercise Science) UCT/MRC Research Unit for Exercise and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, University of Cape Town , South Africa Abstract For the achievement of peak sporting performance, many variables need to be optimized, including physical and mental training, rest, nutrition, team dynamics and tactics. Environmental factors on and around the competition venue may also have a significant impact on performance. This review highlights several important environmental conditions and their possible effect on exercise performance. The factors discussed include temperature, ultraviolet radiation, allergens, atmospheric pollution and altitude. The climatic, atmospheric and weather conditions likely to be prevalent in Beijing at the 2008 Olympic Games are presented and recommendations are provided for optimising performance under these conditions during August, the time at which the Games will be held. Keywords: Olympics, weather, pollution, allergens, performance *Dr Jill Borresen BSc(Med)(Hons), PhD (Exercise Science) Dr Borresen has been part of the UCT/MRC Research Unit for Exercise and Sports Medicine, Department of Human Biology, University of Cape Town, South Africa, while studying for her BSc (Med)(Hons) and PhD degrees. Her main research focus has been heart rate recovery, and quantifying training load. Dr Borresen competed in the Olympic Games in 1996 and 2000 for archery. Introduction For the achievement of peak sporting performance, many variables need to be optimised, including physical and mental training, rest, nutrition, team dynamics and tactics, to name a few. Variations in environmental factors, such as climate and weather, can also have a significant impact on exercise performance; particularly during outdoor endurance events. Factors that may directly affect performance include temperature and humidity, wind speed, visibility, precipitation, cloud cover and heat radiation off surrounding surfaces1. Significant fluid loss in extremely hot environments, for example, may have a negative affect on physiological function, particularly in endurance exercise2;3. Although recognised that some degree of fluid loss may have no adverse effects on exercise capacity4, it remains prudent to attempt to maintain fluid balance. Allergens in the environment must also be considered during training and competition as allergic conditions may impair sports performance, particularly in sports that require a significant increase in ventilation. Likewise, these athletes risk inhaling higher concentrations of airborne pollutants with the increased air flow velocity, which carries pollutants deeper into the respiratory tract5;6. Knowledge of the environmental conditions expected at an upcoming competition is an important component of the preparation towards optimal performance at that event. Athletes competing in the 2008 Olympic Games in Beijing, China, should consider implementing precautionary measures against unfavourable stressors, such as heat, humidity and pollution, in order to optimise their performance under the conditions likely to be prevalent at the Games. Effect of selected environmental conditions on exercise performance Temperature The 2008 Summer Olympic Games will be held from 8-24 August, a time of year characterised by day-time temperatures averaging 30°C and night-time temperatures averaging 20°C. Therefore it is more likely that the effect on performance of these high temperatures will need to be considered. As ambient temperature rises above 20°C the bulk of heat dissipation in the exercising athlete results from the evaporation of sweat3;7. During prolonged exercise in extreme heat, sweat can be lost at rates in excess of 2 l/h-1 7. Significant fluid loss may have a negative affect on cardiovascular capacity and thermoregulatory function particularly in endurance exercise2;3. However, some degree of fluid deficit is tolerable without any adverse effect on physiological function or exercise capacity4. In shorter events there may be no reduction in functional capacity in hot environments2; however, it is still prudent to maintain fluid balance as dehydration may become a concern to short-distance performance if it is induced prior to the event7. For example, a pre-exercise fluid deficit of 1.5-2% of body mass has been found to cause a reduction in performance in events lasting 5-30 minutes2. Any factor that limits evaporation, such as high humidity or dehydration (greater that a 2-3% decrease in pre-exercise body mass), may have profound effects on physiological function and athletic performance as effective cooling is compromised3;8. This is particularly true in hot environments of around 31-32°C, whereas in temperate environments (20��°C) dehydration by 2% of body mass appears to have an insignificant effect on endurance performance9. The most widely used index for measuring heat stress is the wet bulb globe temperature (WBGT) index10: WBGT = (0.7Twb) + (0.2Tg) + (0.1Tdb) where Twb is the wet bulb temperature, Tg is the black globe temperature and Tdb is the shaded dry bulb temperature10. The risk of heat illness due to environment stress can be rated as follows10: Very high risk WBGT above 28°C High risk WBGT 23°C-28°C Moderate risk WBGT 18°C-23°C Low risk WBGT below 18°C Ultraviolet radiation The depletion of the ozone layer is a critical environmental concern as it shields the earth from the sun’s harmful ultraviolet (UV) rays (light of 290-400nm in wavelength). Ozone depletion, as well as seasonal and weather variations, allows different amounts of UV radiation to reach the earth. The UV Index considers the ozone layer thickness, UV incidence (incoming radiation level) on the ground, cloud cover (clouds reduce UV levels) and altitude (UV levels increase by 6% for every 1km of elevation gain). It does not include the effects of variable surface reflection (e.g. sand, water, or snow), atmospheric pollutants or haze, which may nearly double UV exposure strength. Thus the UV Index, which ranks UV radiation levels on a 1-11+ scale, is a useful tool in assessing exposure risk11 (Figure 1). Another indicator (AC10 UV-B trends) reports the amount of UV-B measured as the minimum erythema dose (MED). The MED is the minimum amount of exposure required to produce a perceptible reddening of the skin. The World Meteorological Organisation (WMO) guidelines categorise measured UV-B exposure levels in terms of their seriousness of impact on humans. Ideally UV-B exposures should not exceed ‘moderate’ at any time during the year. Moderate between 0 and 7 MED High between 7 and 14 MED Dangerous between 14 and 24 MED Very dangerous above 24 MED (From: http://www.environment.gov.za/) Allergens Athletes travelling to different geographical locations may be exposed to allergens, including aeroallergens, contact allergens and food allergens. Allergens in the environment must therefore be considered during preparation and sports competitions as allergic conditions may impair sports performance. For the purposes of this review, mainly aeroallergens will be discussed, as these relate to environmental conditions. The main allergy-producing pollens are derived from grasses and trees. Pollen grains need to be smaller than 50 microns to be distributed by the wind. Pollen counts are established by expressing the number of pollen grains counted on each sample as a daily average in pollen grains per cubic metre of air based on a known rate of airflow through the pollen trap. Usually pollen counts of more than 50 grains per cubic metre indicate significant risk to allergy sufferers at rest, but patient sensitivity is extremely variable and many patients can develop allergic symptoms at lower pollen counts12. During exercise, ventilation may increase up to 200 l/min-1 for short periods of time in speed and power events and for longer periods in endurance events13. When the ventilation level exceeds about 30 l/min-1, there is a shift from nose breathing to combined mouth and nasal breathing. This shift in breathing results in a greater deposition of airborne allergens and other inhaled particles to the lower airways. The risk of developing exercise-induced bronchospasm (EIB) increases significantly during the pollen season in asthmatic patients who are allergic to pollen, but not in patients who are allergic to pollen but do not have asthma13. Although some athletes experience improvement in allergic rhinitis with exercise, rhinitis may worsen with exposure to allergens, especially in cold or dry air. Allergic rhinitis has been shown to have negative effects on performance (ability to train and compete)14. Pollutants have also been shown to interact with allergens in inducing sensitisation and triggering of symptoms in allergic subjects14. Finally, in susceptible individuals, contact with grasses and other allergens can result in urticaria (skin allergy). Atmospheric pollution A diverse mixture of suspended particles and gases containing reactive free radical species is released into the atmosphere as a consequence of fuel combustion6. Particulate matter (PM) pollution comprises solids and liquids that are present in the air in particles small enough to remain in suspension for some hours or days5. The particles are classified according to aerodynamic diameter, as coarse (<10 mm; PM10), fine (<2.5 mm; PM2.5) or ultrafine (<0.1 mm; PM0.1) particles. Presently, the air quality standards for PM10 and PM2.5 in the United States and United Kingdom are 50µg.m-3 and 15µg.m-3 respectively as a running 24-hour average5;6. Although athletes are at increased risk of inhaling pollutants, the question of pollutant deposition in the respiratory tract during exercise remains uncertain5. Particulate matter associated with both SO2 and ozone may be deposited in the lower respiratory tract, producing an increase in respiratory symptom exacerbations and deterioration in lung function14. However, the impact of PM10 on athletic performance has not yet been determined15. Given that PM10 induces oxidative stress and inflammation, further research is required to assess the impact of PM10, ultrafine particles and metals on respiratory and cardiovascular function in relation to sports performance15. Ozone (O3) is generated from hydrocarbons and NO2 in the presence of ultraviolet radiation14. A concentration of 100ppb causes decrements in lung function at an exercise intensity equating to a minute ventilation of 70 l/min-1 5, but this is a very high concentration compared to the UK national limit of 50ppb (running 8 hour mean)5. Allergen responses may be exaggerated by ozone14; however, there is high individual variability in response to O3 exposure5. The respiratory discomfort associated with O3 exposure may cause decreases in maximal performance5. Nitrogen dioxide (NO2) is derived mainly from motor vehicles, power stations and industrial processes. There is little or no negative effect as a result of exposure to NO2 in normal subjects. Asthmatics have been shown to experience significant increases in EIB or cold air hyperventilation14 with short-term NO2 exposures of 500ppb; however, NO2 levels in urban environments are usually below 150ppb5. Sulphur dioxide (SO2) begins to affect lung function in normal healthy adults at concentrations between 1000 and 2000ppb. Thus with the recommended air quality standard for SO2 being 100ppb (15 minute average)5, it is unlikely to be of concern to athletes with normal lung function. Asthmatics, however, may be 10 times more sensitive to SO2 than non-asthmatics, especially when exercising. At concentrations of 500ppb exercising asthmatics experience significant changes in airways resistance after just five minutes of exercise, with wheezing, chest tightness, and dyspnoea being experienced5. Air temperature and humidity influence the degree of symptoms experienced, with cold dry air producing a faster and more intense response than warm moist air5. Volatile organic compounds (VOCs) consist of a group of over 100 chemicals formed during incomplete burning of fuel and other organic substances6, many of which are carcinogenic5. There are therefore no safe levels recommended by the World Health Organization. The UK National Air Quality limits are 5ppb for benzene and 1ppb for 1,3-butadiene (running annual mean)5. The area of exercise and the inhalation and possible accumulation of VOCs has received little attention5. International guidelines for selected pollutants include: Nitrogen dioxide (NO2) 200 µg/m3 (hourly mean) (WHO) Sulphur dioxide (SO2) 125 µg/m3 (24-hr mean) (WHO) Ozone (O3) 120 µg/m3 (8-hr running mean) (WHO) Lead (Pb) 0.5 µg/m3 (annual mean) (WHO) Particulates (PM10) 50 µg/m3 (24-hr running mean) (UK) (From http://www.environment.gov.za/enviro-info/sote/citysoe/cape/air_a.htm) Athletes are at increased risk of inhaling pollutants because (1) with increases in minute ventilation during exercise, there is an increase in the concentration of pollutants inhaled, (2) a larger fraction of air is inhaled through the mouth during exercise, thus bypassing normal nasal filtration mechanisms, and (3) the increased air flow velocity carries pollutants deeper into the respiratory tract5;6. Blood toxin levels may quickly reach harmful levels, as was shown in New York City runners after 30 minutes of exercise near busy roads. This evoked an acute rise in blood carboxyhaemoglobin levels from 1.7% to 5.1%. These levels are similar to those found in regular cigarette smokers. During exercise, low concentrations of pollutants (O3 and NO2) were required to cause similar lung damage to that achieved by high concentrations of the same compounds at rest6. Altitude It is widely believed that performance is marginally affected by altitude, with various training strategies being developed and implemented in an attempt to minimise this negative affect. Many athletes and coaches (particularly those in endurance sports) also believe that training at altitude improves sports performance. Variables thought to contribute to this positive training effect are: the level of ascent, the duration of time spent at altitude, the athlete’s level of fitness before arriving at altitude, the intensity and type of training performed at altitude, and the individual variation in response to acclimatisation and altitude training16. Living at altitude induces changes in the physiological systems of the body that are thought to improve endurance exercise performance16. However, early suggestions of the advantages of training at moderate altitudes (1829-3048m) have not been proven over time. When athletes train at moderate altitude their ability to perform at moderate altitudes may be enhanced, but they do not usually improve their maximum exercise performance at sea level17;18. A “threshold altitude” (2200-2500m) has been identified, below which it is unlikely that physiological adaptations will develop that might improve performance. It has been suggested that as far as altitude acclimatisation for sea level performance is concerned, within a reasonable range of 2200-4000m “higher is better”19. However, there may be an associated cost with progressively higher altitudes that may negate the desired effects of acclimatisation. One of these possible negative effects is that athletes may not be able to sustain training at the same level of intensity that they could at sea level, which is necessary to maintain competitive fitness or improve performance18;19. Other potentially negative effects of altitude training may include decreased plasma volume, depression of haemopoiesis and increased haemolysis, increased sympathetically mediated glycogen depletion at altitude, increased respiratory muscle work after return to sea level, immunosuppression, acute altitude sickness and pulmonary oedema 18. Levin and Stray-Gundersen therefore proposed a “Live High Train Low” strategy in which athletes live at 2500-3000m to maximise acclimatisation, but perform high-intensity interval workouts as close to sea level as possible (below 1500m) to maximise running speed and training intensity19. Despite the superiority of living high - training low over traditional altitude or sea level training, there remains substantial individual variability in the magnitude of improvement achieved with such a regimen20. Considerations for optimising performance under selected environmental conditions in Beijing at the 2008 Olympic Games Selected geographical information and average environmental conditions expected during August in Beijing, China are presented in Table 1. Athletes competing at the 2008 Olympic Games can expect hot, humid and wet days with little wind to ease high discomfort levels. High average daytime temperatures (~32°C) were also experienced in 2004 when the Olympic Games returned to Athens, Greece. However, the Mediterranean summer is characterised by little rainfall1, which may have contributed to less humidity (~40%) than is expected in Beijing in August. Athens is also considered one of the most polluted cities in Europe, with its geographic position in a mountain valley and obstructed winds aiding the accumulation of polluted air1. A similar problem is expected in Beijing, where levels of atmospheric pollutants have exceeded global standards for years. These environmental considerations and their relevance to sporting performance are discussed below. Table 1: Geographical information and average environmental conditions expected during August in Beijing, China
* http://www.eurometeo.com/english/climate/city_ZBAA/id_GTx/meteo_beijing%20china # http://web2.airmail.net/danb1/beijing.htm $ http: //www.timeanddate.com/worldclock/astronomy.html Temperature and humidity The summer months in Beijing are characteristically wet and hot, with approximately 60% of the annual precipitation being received during June, July and August. The average precipitation during August is 169mm (Table 1) which, combined with high daytime temperatures and low average wind speeds (mph), creates very high discomfort levels. Average humidity during August mornings is 90% and during the afternoons is 63% (Table 1). The average maximum temperature in August is around 30ºC (Table 1) which, according to the WBGT index, increases the risk of heat illness due to environment stress to very high levels. A combination of high exercise intensity, high air temperatures and high humidity may challenge effective evaporative cooling of the body, especially if exercise is prolonged (>1 hour) or hydration is inadequate8. It has therefore been suggested that fluid balance be monitored at temperatures above about 20°C, when increased sweat rates cause an increase in body fluid loss. Although it is important to prevent dehydration during exercise in the heat, excessive drinking is also detrimental to performance and dangerous to health. Noakes warns that the over-consumption of fluid before, during, or after exercise is unnecessary, and can have a potentially fatal outcome4. He advises that “drinking according to the personal dictates of thirst seems to be safe and effective. Such fluid intake typically ranges between 400ml and 800ml per hour in most forms of recreational and competitive exercise; less for slower, smaller athletes exercising in mild environmental conditions, more for superior athletes competing at higher intensities in warmer environments”4. Furthermore, each athlete responds differently to heat stress and therefore athletes should be monitored on an individual basis2;10. This can easily be achieved by weighing the players before and after training and matches to ensure that changes in body mass are compensated for by fluid ingestion during the recovery phase. Clothing with fabric characteristics that minimise heat storage and maximise sweat vaporisation may also be an important consideration8. In the event of extremely high temperatures being experienced, policies regarding the time of day for scheduling events, and the possibility of postponement or cancellation of events would have to be considered by the organisers at this venue. Methods of pre-cooling have been investigated for their potential to reduce thermal strain and improve sports performance in extremely hot conditions. However, the effectiveness and practicality of using many of the available methods remain inconclusive21. A period of acclimatisation, of approximately 1-2 weeks, may assist the athlete to adapt to exercising in hot conditions by improving thermoregulatory responses8;10. Acclimatisation has been shown to reduce physiological parameters, such as heart rate, rectal temperature, blood lactate, and blood glucose concentrations, that are increased in the heat7. Immediate treatment of exertional heatstroke may include cool water immersion, application of wet towels and ice packs to the neck, under-arms and groin areas; all of which have been used successfully10. Ultraviolet radiation Exposure to the sun is associated with different types of skin cancer, accelerated skin aging, eye diseases, such as cataracts, and there is also evidence of reduced effectiveness of the immune system. Sun protection is therefore an important precaution that should be taken against UV radiation. Time spent in the sun during midday hours should be limited. Athletes should wear protective clothing, such as a hat that shades the eyes, face and neck, as well as protective eyewear. A sunscreen that has a minimum sun protection factor (SPF) of 15+ should be applied to exposed skin regularly22. The maximum UV radiation index reported for Beijing is 8, which is regarded as dangerous (Figure 1). According to the World Meteorological Organisation, UV-B exposures should not exceed ‘moderate’ at any time during the year. Therefore the above precautionary measures should be taken at the 2008 Olympic Games. Allergens The main allergy-producing pollens are derived from the grasses, but trees may also produce pollen which can cause symptoms. Ouyang et al. investigated the species composition, distribution and phonological characters of pollen-allergenic plants in the Beijing urban area and found that pollen-allergenic plants were most diversified in urban parks and had the highest proportion in street tree species23. The coverage of pollen-allergenic herbs was greatest in waste lands, followed by gym centres and institution yards, greenbelts, parks, residential areas and lowest in squares. The blooming period of pollen-allergenic trees in Beijing is March and April, whereas that of the herbs is July to September23. Wang et al. investigated which aeroallergens were prevalent in Beijing in 554 allergic rhinitis patients. They found that dust mite was most prevalent (D. farinae 64.6% and D. pteronyssinus 64.3%) followed by flower pollen (28.7%) and herbs (26.5%)24. Yu et al. studied the distribution of 12 pollen taxa across China25. They found that a southward dispersal was dominant and that these pollens may be transported up to 1000km due to several months of persistent north winds from the winter monsoon. The second highest pollen dispersal direction is toward the east, which occurs mainly with the pollen of Larix, Abies, Picea, Betula and Acer plants. These pollen dispersals are influenced by the westerly winds in the mid-latitudes of China. The pollen of summer-green and evergreen trees (Platycarya, Fagus and Cyclobalanopsis) in eastern and southern China have relatively high northward dispersal, due to the Asian summer monsoon25. The risk of developing EIB symptoms increases significantly during pollen season in asthmatic patients who are allergic to pollen13. Athletes in particular may be at greater risk of developing EIB during exercise when ventilation rate and depth are increased resulting in a greater deposition of airborne allergens and other inhaled particles to the lower airways13. Maximal exercise capacity may decrease as a result of increased ventilatory cost and decreased maximal ventilatory capacity. The susceptible athlete may also develop upper respiratory tract infections (URTI) due to increased bronchial responsiveness and airway inflammation13. It is therefore important to test athletes well before competition so that the susceptible individuals and the pollen causing the allergy can be identified and the athletes treated prophylactically. General recommendations for the management of athletes with predispositions to allergy include: 1. Early recognition and diagnosis 2. Allergy testing prior to competition (aeroallergens, trees and grasses) 3. Recognition of associated or sub-clinical asthma through adequate pulmonary function tests 4. Avoidance of exposure to relevant allergens and pollutants during exercise. 5. Medical treatment to improve allergic symptoms without affecting athletic performance while complying with anti-doping regulations14. Atmospheric pollution Beijing is located in a topographic trough which alters wind flow, decreases wind speed, and consequently contributes to the formation of a pollution convergence zone26. Li et al. found that two areas in Beijing were heavily polluted by aerosol pollutants: downtown Beijing and near the Xishan Mountain (south-west of downtown)26. High concentrations of particulate matter and other pollutants (O3, SO2, NOx) have been recorded in Beijing’s urban atmosphere, and has been attributed largely to fossil fuel combustion27;28. During 2000-2004 the annual concentration of particulate matter with aerodynamic diameters less than 10µm (PM10) ranged between 141 and 166µg.m-3; nearly three times the Grade 1 national standard of 50µg.m-3 28. It is estimated that fine particles, i.e. with a diameter less than 2.5µm (PM2.5), could account for 60% of the PM10 concentration. In turn, organic matter may constitute 30%-50% of the total mass of fine particles (PM2.5) in Beijing27. In the summer of 2002-2003, mass concentrations of PM2.5 averaged 66µg.m-3 and organic compound concentrations of 502µg.m-3 were reported27. Hu et al found PM10 and PM1.8 concentrations of 249.35µg.m-3 and 170.68µg.m-3 respectively between 13 July and 23 August 2004, and reported that fine particle pollution became severe under conditions of high temperature and high relative humidity, resulting in low visibility (2.5km)29. The impact of particulate matter, and in particular fine particles (PM2.5), on human health is a concern, especially since some organic compounds have proven to be mutagenic and carcinogenic27;28. With air quality assurance being an important factor to be considered for the Games, the Beijing local government has introduced projects and measures to address these concerns. In August 2007, it was reported that the city had spent US$240 million in research and development for relevant technologies and facilities to produce a “green” Olympics30. Fourteen electric buses and 1300 buses using compressed gas began operating in Beijing as part of the campaign towards the 2008 goal of having 80% of buses and 70% of taxis fuelled by clean energy. The city has also been working to limit automobile exhaust by introducing a 4-day traffic ban in September which decreased pollutants by about 5 815 tons; a trial run of the system proposed for the Games. Last-minute measures, such as the proposed closing of all construction sites six months before the Games, have also been considered30. As previously mentioned, it has been documented that strenuous exercise in heavy traffic for 30 minutes can increase the level of carboxyhaemoglobin 10-fold, which is equivalent to smoking 10 cigarettes. Experimental evidence confirms the detrimental effect that carbon monoxide (CO) has on athletic performance5. Hence it is prudent to always train away from traffic to avoid or minimise exposure to airborne contaminants. The length of time spent exercising is another very important factor. Ultramarathon runners and others participating in endurance events, for example, walking and cycling, are likely to be most at risk from the negative and harmful effects of pollution exacerbated by exercise5;6. Altitude The city of Beijing lies at an altitude of 55m (Table 1), making the negative affects on performance of competing at altitude less of a concern at the 2008 Olympic Games. With regard to training at altitude in order to improve performance at sea level, it has been found that when athletes train at moderate altitudes (1829-3048m) their ability to perform at moderate altitudes may be enhanced, but their maximum sea level performance is not usually affected17;31. The possibility, however, that the design of these studies is inadequate to detect an effect of less than 2%-3% cannot be ruled out; an effect that would far exceed what is required by elite athletes (<1%) to win medals or improve their personal performance31. Studies investigating positive physiological changes at altitude (or under hypoxic conditions) that are reported to improve performance have been set at altitudes much higher than 2000m. A “threshold altitude” of between 2200m and 2500m has been identified, below which it is unlikely that physiological adaptations will develop that might improve performance20. Subjective coaching opinion appears to suggest that 3 weeks at altitude is sufficient to induce performance-enhancing adaptations, and that performance is optimised after 14 days at sea level after a bout of altitude training; however, there is no scientific evidence to support this18. Summary Knowledge of the environmental conditions expected at an upcoming competition is an important component of the preparation towards optimal performance at that competition. This paper provides details of some important environmental conditions likely to be prevalent in Beijing at the 2008 Olympic Games, along with their possible effect on performance. Since Beijing has an altitude of only 55m (well below the “threshold altitude” of 2200-2500m19), it is unlikely that any physiological changes will occur that may have an appreciable influence on performance. Hot, wet and humid conditions can be expected in August in Beijing. Thus these factors, along with the exercise regime to be performed in these conditions, should be monitored. The appropriate clothing should be worn and other precautions taken to avoid UV exposure, and personalised attention should be given to hydration and exertion to reduce the risk of hyperthermia. Given that the pollen-producing period of allergenic herbs in Beijing is July to September, and that dust mite has been found to be the most prevalent aeroallergen in allergic rhinitis patients, it is recommended that all athletes are exposed to the dominant aeroallergens well before the Games to identify those who may be susceptible and who should be treated prophylactically. The greatest concern to athletes at the 2008 Beijing Olympic Games is undoubtedly the high pollution levels. Although efforts have been made to reduce pollution in time for the Games, it is unclear how the International Olympic Committee will determine whether acceptable levels have been met, and what will be done if they have not30. The postponement of events at the Games is not beyond the realm of possibility30. Until these decisions are made, however, athletes should make every effort to minimise their exposure to airborne contaminants and the time spent exercising in these conditions. Acknowledgements Professor Martin Schwellnus, for his guidance in writing and editing this article. Funding was received in part by the University of Cape Town and Discovery Health. Address for correspondence: Dr Jill Borresen (or c/o Assoc. Prof. Mike Lambert), UCT/MRC Research Unit for Exercise and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, 3rd Floor, Sports Science Institute of South Africa, Boundary Road, Newlands 7700, South Africa Tel.: +27 (21) 650 4561 Fax: +27 (21) 686 7530 Email: Jillsbow@yahoo.com References 1. Peiser B, Reilly T. Environmental factors in the summer Olympics in historical perspective. J Sports Sci 2004; 22 (10): 981-1001. 2. Maughan R, Shirreffs S. Exercise in the heat: Challenges and opportunities. J.Sports Sci. 2004; 22 (10): 917-927. 3. Coris EE, Ramirez AM, Van Durme DJ. Heat illness in athletes: The dangerous combination of heat, humidity and exercise. Sports Med. 2004;34 (1): 9-16. 4. Noakes TD. Overconsumption of fluids by athletes. BMJ 2003;327 7407): 113-114. 5. Carlisle AJ, Sharp NC. Exercise and outdoor ambient air pollution. Br J Sports Med 2001; 35 (4): 214-222. 6. Sharman JE, Cockcroft JR, Coombes JS. 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