POLLUTION AND PERFORMANCE

THE MAIN POLLUTANTS THAT AFFECT EXERCISE PERFORMANCE

Ozone (O3) Ozone (O3) is a highly reactive photochemical oxidant, produced by the action of sunlight on volatile organic compounds (VOCs) and

nitrogen oxides (NOx) derived from combustion sources, principally road vehicles. Thus, air ozone concentration is worse on sunny days, peaking in the middle of the day. Human exposure to elevated ozone concentrations can give rise to inflammatory responses and decrements in lung function. Symptoms observed on exposure to high levels of ozone include cough, chest pain, difficulty in breath- ing, headache and eye irritation. Research indicates a large inter- individual variation in response to ozone exposure and the effects seem to be more pronounced in children than in adults. Exposure

to O3 causes inflammation of the lining of the lung resulting in a decreased lung function as evidenced by a fall in FVC and FEV1 (1). Ozone appears to exert its inflammatory effect by chemically react-

ing with the components of the fluid lining of the lung leading to the generation of free radicals and oxidative stress.

Nitrogen oxides (NOx) Nitrogen oxides (NOx) are a family of highly reactive gases includ-

ing nitrogen dioxide (NO2) and nitric oxide (NO) that form when fuel is burned at high temperatures. They emanate principally from motor vehicle exhaust and stationary sources such as electric utili- ties and industrial boilers. NOx play a role in the atmospheric reac- tions that produce ground-level ozone pollution. Sunlight, VOCs and

NOx are needed to generate O3 and so NOx levels decline as O3 is photochemically generated. In the lungs NOx can also generate free radicals (2) with resultant inflammation. In addition, NOx exposure lowers resistance to respiratory infections such as upper respirato- ry tract infections (URTIs) and influenza.

Particulate matter (PM10) PM10 are particles small enough to reach the airways and lower regions of the respiratory tract during ventilation. Major adverse health effects arising from acute exposure to increased levels of PM10 include exacerbation of disease in chronic obstructive pulmonary disease (COPD) and asthma patients. In addition the elderly, and patients with cardiovascular disease show increased mortality in association with increased PM10. Acute effects on healthy individuals occur only at much higher levels. PM10 is considered to have its adverse effects as a result of oxidative stress- mediated inflammation (3).

The impact of pollution on exercise

Of all the pollutants of concern, O3 and its impact on health and exercise has received the greatest amount of attention in the liter- ature. It is known that exposure to ozone results in respiratory dis- comfort and reduces pulmonary function (4). Studies assessing the impact of ozone on lung function and exercise have been performed in lab and field based settings. Studies have commonly reported that subjects experienced symptoms that included cough, throat tickle, headache, breathlessness and impaired lung function that may be increased in intensity in exercising individuals due to increased ventilation rates. Further, decreased submaximal and maximal exercise performance has been reported (5).

There is limited research examining the impact of NOx and PM10 upon exercise. Increases in airway resistance and pulmonary dys-

www.sportex.net function following acute exposure to very low and very high con-

centration levels of nitrogen dioxide (NO2), however, may result in a reduction in exercise capacity (6). In addition, the known oxida- tive stress associated with exposure to PM10 suggests they are like-

ly to act in a similar fashion to O3 causing inflammation and affect- ing athletic performance. Again the impact for asthmatics may be greater than that experienced by non-asthmatics.

POLLUTION AND ASTHMA

Long and short-term exposure to pollution, such as NO2 and ozone, is associated with an increase in asthma severity. Laboratory inves-

tigations examining the short-term effects of NO2 have shown that lung function is reduced in individuals with and without asthma (7). Asthmatic individuals, however appear to be more sensitive to

very low NO2 concentrations. Short-term exposure to ozone, even at low concentrations, has been reported to be the main trigger leading to an increase in asthma severity, medication use and symptoms in children with asthma (8). The introduction of exercise in polluted environments may cause a further increase in asthma severity. Scannell et al (9) reported that adult asthmatics increased their risk of severe respiratory tract inflammation when exercising for 4 hours in an ozone-polluted environment.

Long-term exposure to pollution is associated with an increased risk of the development of asthma. Exercising and living in polluted environments may further increase the risk of developing asthma, which may have an impact on individuals who complete a high vol- ume of exercise regularly such as elite athletes. McConnell et al (10) reported that children who take part in three or more sports at school and live in areas of high ozone concentration for several years are at greater risk of developing asthma/exercise-induced asthma than those who are less active and live in the same area or those who live in a low ozone concentration area.

COMBATING THE EFFECTS OF POLLUTION A number of strategies have been suggested to reduce the impact of pollution on performance (see Box 1.). Obvious strategies includ- ing exercising in the early morning or late evening and in windy exposed areas, will help exercisers avoid pollution. The use of carbon impregnated masks may be of some value in reducing the

impact of O3 and NOx, however the requirement for ultra-fine filtration for PM10 would be likely to lead to a saturated filter in a very short period of time during exercise. Other suggestions include acclimatisation and anti-oxidant supplementation.

Acclimatisation

Recent work has suggested that repeated exposure to 4 hours NO2 on four consecutive days results in reduced neutrophil numbers in the bronchial epithelium and a reduced (not abolished) impact of

NO2 on lung function, suggesting that we can become somewhat acclimatised to NO2 exposure. Limited data exists supporting the notion of acclimatisation to O3 exposure, however, a plateau and possible improvement in lung function has been documented fol- lowing a period of adaptation to ongoing (36h to 5 days) exposure

to O3 (11). These data suggest that a minimum of 2 days and up to 5 days represents the window of opportunity to optimise lung function and performance in a polluted environment.

Anti-oxidants Oxidative stress arises in the lung following pollution exposure and

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