conditions on changes in bronchial responsiveness to methacholine during a training and competitive season was studied in 19 high-performance.
Scand J Med Sci Sports 1995. 5: 152-159 Printed in Denmark All rights reserved
Copyright 0 Munksnaard 1995 Scandinavian Journal o f M E D I C I N E & SCIENCE IN SPORTS ISSN 0905-7188
. . . . . The influence . .01 training intensity, airway infections and environmental conditions on seasonal variations in bronchial responsiveness in cross-country skiers f i .
Heir T, Larsen S. The influence of training intensity, airway infections and environmental conditions on seasonal variations in bronchial responsiveness in cross-country skiers. Scand J Med Sci Sports 1995: 5: 152-159. 0 Munksgaard, 1995 The influence of physical training, airway infections and environmental conditions on changes in bronchial responsiveness to methacholine during a training and competitive season was studied in 19 high-performance male cross-country skiers 19-21 years old. The longitudinal changes in the methacholine concentration required for a 10% fall in FEVl (PC,,) were negatively correlated with the changes in the volume of physical activity at an intensity level above 90% of maximal heart rate. The variation in physical activity at this intensity level accounted for 54.8% of the change in PClo.No association was found, however, with regard to physical activity at lower intensity levels. Seasonal variation in PClo was not associated with the changes in occurrence or duration of airway infections provided that the PClomeasurement was postponed for 3-6 weeks after the onset of a recent infection. Seasonal variation in PClo seemed not to be associated with variations in ambient levels of air pollutants or aeroallergens. PClo was lowest at the end of the coldest part of the year. In conclusion, seasonal variation in bronchial responsiveness in high-performance crosscountry skiers could to a great extent be explained by changes in the volume of physical activity at a very high intensity level.
Seasonal variations in bronchial responsiveness (BR) are well described (1, 2). We have previously reported that BR to methacholine increases reversibly in highperformance cross-country skiers during the winter, an observation contrary t o the findings in a control group, which demonstrated their lowest degree of BR on the same occasion (3). Several environmental stimuli have both experimentally and in natural settings been shown to induce transient enhancement of BR to histamine or methacholine in both asthmatic subjects and normals (4). The stimuli include inhaled allergens, chemical sensitizers, respiratory viral infections, and noxious gases such as sulfur dioxide, nitrogen dioxide and ozone. Controversies remain as t o whether cold air inhalation (5-7) or exercise (8, 9) has any effect on BR in healthy subjects. It has been postulated that
T. Heir', S. Lacsen* 'Norwegian University of Sport and Physical Education, Oslo, 2Medstat Research, Lillestrem, Norway
Key words: airway responsiveness; bronchial provocation test; exertion; skiing; respiratory tract infection Trond Heir, Asalveien 1, N-0876 Oslo, Norway Accepted for publication June 9, 1994
such provoking factors that cause a transient increase in BR may also, occasionally, result in a permanent increase in BR (4). Many factors have to be evaluated in the pathogenesis of enhanced BR in athletes. They are, for instance, known to be more susceptible to enhanced BR following airway infections than non-athletic controls (10). Thus, seasonal variations in the prevalence of airway infections have to be considered. Moreover, heavy training and competitions under low ambient temperatures result in significant amounts of cold air inhalation. Also, the level of air pollutants or aeroallergens in the tracheobronchial tree during exercise is much higher than during rest because of the higher ventilation, oral breathing and decreased time of contact with upper airways (1 1). Based on previously published data concerning
Bronchial responsiveness and cross-country skiing seasonal variation in BR in high-level cross-country skiers (3), the present study reports the influence of physical training, airway infections and environmental conditions on changes in BR.
Material and methods Subjects Nineteen high-performance male cross-country skiers 19-21 years of age were followed from July 1988 through June 1989 (3). The skiers were picked to undergo their compulsory military service in a special setting for elite athletes during the 12-month study period. A control group consisted of 22 male recruits matched for age and localized in the same camp as the skiers. All subjects were nonsmokers and none suffered from bronchial asthma or other lung diseases. Two skiers had a history of atopy: one was allergic to cat dander and the other to house dust mite. Six control subjects had a history of atopy, but only 3 of them were allergic to airborne allergens (pollen). The study was approved by the local ethics committee. All subjects signed an informed consent form before participating in the study.
Methacholine inhalation tests The subjects underwent a methacholine inhalation test in August, November, February and June as previously described (3). Nebulized methacholine was inhaled in consecutively doubling concentrations in the range from 2.0 to 128.0 mg/ml. BR was expressed as the test concentration causing a fall in the FEV, by lo'% from the initial saline inhalation (PC,,). An inverse relation was defined such that BR decreased linearly as the number of twofold concentration steps required for a 10% fall in FEV1, increased (BR--log PClo). Challenges were postponed for 3 and 6 weeks after the onset of a respiratory infection. The latter test was used in evaluating the results if the subject did not contract another airway infection before 6 weeks had elapsed. If he did, the test performed 3 weeks after the onset of symptoms was used, or the test was once more postponed for 3 weeks. No physical activity was permitted on the day before the test.
Physical activity The subjects kept a record of their endurance training. They reported at the beginning of each month the amount of exercise that had generated a heart rate (HR) above 60% of maximum H R (HR,,,) the previous month. Furthermore, they reported how much of the exercise had resulted in heart rates above SO%, and 90% of HR,,,, respectively. The subjects did this by regularly counting the HK during training by
finger palpation of the carotid artery while exercise was stopped or slowed down for 10-15 s. Interval training was carried out with H R measurements at the tempo shifts; the long slow distance training was done with less frequent measurements. The registration was unsystematically compared with HR recorded continually with Sport Tester with a memory (PE 3000, Polar Electro, Finland), which generally confirmed the reports based on manual counts. HR,,, was recorded at the time when entering the study while running on a treadmill at an inclination of 6" and a gradually increasing speed to complete exhaustion (5-7 min). During this all-out test, the HR was recorded continually with telemetric equipment (Danika, Denmark). Cross-country skiing, sometimes substituted by running, was the dominating training activity from November through March. Running, roller skiing, uphill walking or bounding and some bicycling constituted the activities during the rest of the year. Some body-building was carried out every month but was generally not included in the registration of endurance training.
Respiratory infections The subjects recorded all symptoms of respiratory infections including running nose, nasal congestion, sneezing, scratchy or sore throat, cough and hoarseness, and such systemic symptoms as feverishness, myalgia and headache. Oral and written information were given on how to register the various clinical symptoms. The subjects were instructed to consult the physician in the military camp for verification of the diagnosis. The physician based the diagnosis of a respiratory infection (RI) on the history of an illness of acute onset either of the nasal cavity, middle ear, sinuses, pharynx, larynx, trachea or bronchi, characterized by local respiratory symptoms, local clinical inflammation, and occasionally accompanied by mild systemic symptoms. In one third of the cases the physician could not be consulted and the diagnosis was based entirely on the symptoms described by the subjects. R I was said to be present when 2 or more local symptoms occurred for 2 or more days or when one local symptom with the exception of sneezing lasted for 3 or more days. Symptoms recurring less than 1 week after a previous infectious episode were regarded as a recurrence or complication of the primary infection. The duration of the illness was defined as the number of days with at least one clinical symptom.
Te mperat u re, po IIut io n and ae roalIe rge ns The monthly mean air temperatures of the military training school area were obtained from climatological bulletins of the Norwegian Meteorological Institute, Oslo. The monthly mean ambient air concen-
Heir & Larsen trations of sulfur dioxide (SO,), nitrogen dioxide (NO2) and ozone (03), were obtained through the National Environmental Monitoring Programme, State Pollution Control Authority, Oslo. Monthly mean air concentrations of pollen (alder, hazel, birch, grass, mugwort) and moulds were furnished by the Department of Botany, University of Trondheim.
Statistical methods Results are expressed as mean values with 95% confidence intervals calculated by the Student procedure (12). In the evaluation of PClo, logarithmic transformation of the data was used. Seasonal changes in the indicators of exercise and RI were calculated using 3 average values from time periods of equal duration; the autumn (September, October, November), winter (December, January, February) and spring (April, May, June). The tests were two-tailed and differences were considered statistically significant if the P-values were less or equal to 0.05. Changes within groups were evaluated by the Student test for paired samples (1 3) with Bonferroni's correction of the significance level (14). The Pearson correlation analysis (12) and stepwise regression model (15) were used to detect variables describing changes in BR.
cantly in the skiers from a mean of 35.7 h in July to 64.8 h in November, but decreased significantly during the winter and spring (Fig. 1). In the control group the mean duration of physical activity varied between 2.8 and 5.1 h per month during the study period (Fig. 1). No significant correlation was found between the changes in PClo and the changes in total volume of physical activity in any of the study groups (Table 2). Training at an intensity level above 80% of HR,,, increased significantly among the skiers from a mean of 8.5 h in July to 12.2 h in November (Fig. 2). It decreased significantly to a plateau between 9.1 and 10.4 h in December through March, and then decreased further during the spring to 5.2 h in June. No significant correlation was found between the changes in PClo and changes in training at an intensity level above 80% of HR,,, (Table 2). Physical exertion at the highest intensity level above 90% of HR,,, increased significantly during the autumn and winter period from a mean of 1.9 h in July to a plateau between 6.2 and 5.9 h in January through March (Fig. 2). It then decreased significantly during the spring to 1.9 h in June. The changes in PClo were negatively correlated with the changes in physical activity at the highest intensity level ( r = -0.74; P