Exercise-induced bronchoconstriction (EIB) is the transient narrowing of the airways after exercise. This phenomenon is common in athletes who may have no diagnosis of asthma or even no respiratory symptoms [1] - [4] . The child, athlete or atopic patient is prone to exercise-induced bronchoconstriction. Rhinitis or respiratory infection during exercise may predispose to exercise-induced bronchoconstriction [3] [5] . Johansson et al. [6] reported a prevalence of EIB in the general population of approximately 5% to 20%. Study by Burnett et al. [7] has shown that the prevalence of EIB is relatively high (18% to 34%) in athletes participating in both individual and team sports. It also varies according to the type of sport, the ventilatory demands and the environmental conditions in which the sport is performed.

Boulet & O’Byrne [2] showed a higher prevalence of EIB in elite athletes compared to the general population (21% vs. 10%). Similarly, studies by Anderson & Kippelen [8] and Carlsen et al. [5] have shown that the prevalence of EIB in athletes trained for high-level endurance events ranges from 10% to 55%. It is, therefore, not surprising that high performance endurance athletes who train in a hot, humid and polluted environment have an increased prevalence of several respiratory diseases such as asthma, rhinitis and EIB compared to non-athletes [9] [10] .

While Exercise-induced bronchoconstriction is strongly correlated with hot, humid conditions and exercise levels, it should also be noted that EIB can be triggered by pollutants such as fine particles. The Higher Institute of Physical and Sports Education is a university facility located near major roads with dust-covered playing fields. It is also close to the largest market in the capital, where the unhygienic environment and garbage odors can cause respiratory problems.

The aim of this study was to assess the prevalence of bronchospasm in students of sciences and techniques of physical activities and sports exercising in a hot, humid environment relatively polluted with fine particles. We hypothesized that football, which is a long-duration, intermittent sport played in a hot, humid environment, might affect lung function and induce bronchospasm in students.

The general characteristics of the students in both groups (EIB− vs. EIB+) are presented in Table 1 (age, height, weight and body mass index (BMI) and forced expiratory volume in the first second (FEV1). The comparison of the FEV1 and PEFR values before the football match and 5 minutes after the match showed a 10% decrease in FEV1 in 5 students ( Table 1 ). This result allowed us to divide the students into two groups: EIB+ group (n = 5) and EIB− group (n = 17) ( Table 1 ).

Notes: EIB−, non-bronchospasm-positive subjects; EIB+, bronchospasm-positive subjects, SEM, standard error of the mean; BMI, body mass index; FEV1, forced expiratory volume in the first second; *Significant difference, between before-exercise versus after exercise (p < 0.05). Υ, fall of 10% or more of FEV1, expressing positivity to exercise-induced bronchospasm.

Post-match FEV1 decreased significantly by at least 10% in 5 subjects, or 22% and PEFR decreased significantly by at least 15% in 8 subjects, or 36% in EIB+, without however showing a significant decrease in EIB− subjects ( Table 2 ).

Notes: EIB+, bronchospasm-positive subjects; EIB−, non-bronchospasm-positive subjects; n, number of subjects; FEV1, forced expiratory volume in the first second; FVC, forced vital capacity; PEFR, peak expiratory flow rate.

The comparison between values for FEV1, FVC, peak expiratory flow rate (PEFR) decreased significantly after compared to before the soccer match in EIB+ (P < 0.002) ( Table 3 ). There was no significant change before and after the match in EIB− (P > 0.05) ( Table 3 ).

The results in Table 4 show that PM2.5 and PM10 concentrations measured in the vicinity of the pitch throughout the soccer match were well in excess of WHO 24-hour limits. It appears that the ambient temperature recorded at the start of the first period was 32.4˚C and increased to 35.3˚C at the end of the second period with a mean standard deviation of 34.22 ± 1.38 and the relative humidity recorded at the start of the first period was 48.3℅ and increased to 59.3 ℅ at the end of the match with a mean standard deviation of 52.2 ± 4.97.

Notes: SEM, standard error of the mean; EIB−, non-bronchospasm-positive subjects; EIB+, bronchospasm-positive subjects; FEV1, forced expiratory volume in the first second; FVC, forced vital capacity; PEFR, peak expiratory flow rate; *Significant difference, between before-exercise versus after exercise (p < 0.05).

Notes. WHO, World Health Organization; PM2.5, Particulate matter or fine particles with a diameter of less than 2.5 µm; PM 10, Particulate matter or fine particles less than 10 µm. The results in Table 4 show that PM2.5 and PM10 concentrations measured in the vicinity of the pitch throughout the soccer match were well in excess of WHO 24-hour limits.

The main results of this study show a prevalence of exercise-induced bronchospasm of 22% in students. We also showed a decrease in forced vital capacity and peak expiratory flow. The decrease in these last two parameters is due to airway obstruction, a disturbance in lung function and supports the idea of exercise-induced bronchospasm. There was also an increase in the concentrations of PM2.5 and PM10 measured around the pitch throughout the match. These parameters are above the values set by the WHO.

The prevalence of EIB is estimated to be between 5% and 20% in the general population [12] , reaching 90% in asthmatic subjects [2] . In the present study, non-asthmatic students were susceptible to EIB, with a prevalence of 22% ( Table 2 ). The DEP is also one of the criteria for determining the EIB. It decreased by 36%, confirming the EIB in these athletes ( Table 2 ). This prevalence is higher than in the general population (5% - 20%), but lower than the EIB prevalence reported in elite athletes [9] . Our result corroborates that of the study carried out by Nsompi et al. [13] , reporting a prevalence of 33% among athletes in hot and humid environments. Athletes who train in cold air environments and/or a dry atmosphere may be more susceptible to bronchoconstriction and have a higher prevalence [14] . On the other hand, due to the significant circulation of air during exercise, the respiratory tract of these athletes is often exposed to numerous allergens and particles (PM2.5 and PM10). Indeed, the concentrations of PM 2.5 (78.79 ± 23.117 µg/m³) and PM10 (109.33 ± 29.672 µg/m³) measured near the student’s property were much higher than the reference values in 24 hours ( Table 3 ). The WHO recommends levels of 15 µg/m³ for PM 2.5 and 45 µg/m³ for PM 10 in 24 hours. The studies by Weiler et al. [9] showed that the prevalence of EIB varies depending on the environment in which the sport is practiced, the type of sport and the maximum intensity achieved.

It should be noted that the environment in which the match took place in our study was polluted. In fact, the land is located near major roads and a large market. This causes the air to be polluted by combustion engines, in particular fine particles and detritus, considered to be very harmful to the respiratory tract [15] . Giles et al. [16] and Rundell et al. [15] claimed that pre-exposure to diesel exhaust significantly attenuated the respiratory effects of physical activity on lung function. In the present study, the ambient temperature and relative humidity were 34˚C and 54%, respectively, with values of 35˚C and 59% at maximum. Our results are consistent with those reported by Maughan et al. [17] , who demonstrated that in a warm environment (30˚C) with relative humidity levels of 24%, 40%, 60% and 80%, the ability to exercise at 70% of the Maximum oxygen consumption deteriorates as humidity increases. Although beneficial, exercise requiring intense effort, performed in unfavorable environmental conditions, is also likely to cause respiratory distress and EIB [3] . Indeed, the prevalence of EIB of 22% observed in our subjects is different from that reported by Wilber et al. [14] . This can be explained by the fact that bronchoconstriction is influenced by several variables, including environmental and climatic conditions, as demonstrated by the studies of Burnett et al. [7] . These authors showed that the prevalence of EIB among athletes practicing individual and team sports varies between 18 and 34%. This variation depends on the type of sport, ventilatory demands and the environmental conditions in which the sport is practiced. In our study, football was played in a hot, humid and polluted environment. These three factors together could explain this high prevalence of EIB.

We showed a significant decrease in post-exercise PEF (7.75 ± 2.08 (l∙s⁻¹) vs. 6.62 ± 1.40 (l∙s⁻¹)) and post-exercise FVC (4.51 ± 0.54 (l) vs. 3.76 ± 0.58 (l)) in EIB (+) students ( Table 3 ). These results show that football resulted in a reduction in lung function capacity. Our results are consistent with those of Zavorsky et al. [18] and Nsompi et al. [13] , who showed an acute decrease in FEV1, PEF and FVC after prolonged exercise in amateur runners and professional long-distance runners, respectively. The authors reported that the decreases in these parameters after prolonged endurance exercise suggest ventilatory dysfunction and/or impaired lung function in individuals with of EIB. Furthermore, Smith et al. [19] reported that this alteration, associated with air pollution, may lead to respiratory dysfunction and respiratory muscle fatigue.

Physical education and sports classes must be taught very early in the morning, when traffic is less dense. In addition, the state should build schools away from main roads so that pupils and students are not exposed to automobile pollutants. Indeed, the latter are likely to cause respiratory and blood diseases. However, there are some limitations of the method, such as the small sample size, false positives and negatives, reproducibility, signs and symptoms mismatch and safety concerns. Other limitations are linked to the lack of measurement of PM2.5, PM10, temperature, and humidity continuously throughout the match. So, it is worth noting that the differences reported in our study may only be within-group changes. Given the importance of the issue, future studies should include a larger sample.

The aim of this study was to assess the prevalence of exercise-induced bronchospasm in first year undergraduate exercise science and technology students working in a polluted environment. In our study, we reported a decrease in FEV1 and PEFR after exercise, i.e. a susceptibility rate to exercise-induced bronchospasm of 22 % and 36 % respectively, associated with a decrease in forced vital capacity, suggesting a decrease in pulmonary compliance or small airway closure. The football match took place in a hot and humid environment with high levels of particulate matter, well above the WHO 24-hour standard. These factors are likely to exacerbate the change in lung function parameters and increase the incidence of exercise-induced bronchospasm.

Authors acknowledge the immense help received from the scholars whose articles are cited and included in references of this manuscript. The authors are also grateful to authors/editors/publishers of all those articles, journals and books from where the literature for this article has been reviewed and discussed.

The study designs were approved by Institutional Ethics Committee of High institute of physical education and sport, Marien Ngouabi University, Brazzaville, Republic of Congo. A letter of consent was obtained from all participants.