3-Min step test and treadmill exercise for evaluating exercise-induced asthma

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1 Eur Respir J 2004; 23: DOI: / Prited i UK all rights reserved Copyright #ERS Jourals Ltd 2004 Europea Respiratory Joural ISSN Mi step test ad treadmill exercise for evaluatig exercise-iduced asthma G. Tacredi*, S. Quattrucci*, F. Scalercio*, G. De Castro #, A.M. Zicari #, E. Boci }, S. Cigolai*, L. Idiimeo #, F. Midulla* 3-Mi step test ad treadmill exercise for evaluatig exercise-iduced asthma. G. Tacredi, S. Quattrucci, F. Scalercio, G. De Castro, A.M. Zicari, E. Boci, S. Cigolai, L. Idiimeo, F. Midulla. #ERS Jourals Ltd ABSTRACT: A simple exercise test would be useful for detectig exercise-iduced asthma, a commo problem i asthmatic childre. The curret study compared the 3-mi step test with treadmill exercise for evaluatig exercise-iduced asthma i asthmatic childre ad assessed whether resposes to both tests are iflueced by baselie lug fuctio ad habitual physical activity. A series of 154 asthmatic childre (84 male childre; mea age yrs) uderwet a 3-mi step-test ad treadmill testig o differet days withi a week at least 24 h apart. Before both tests each subject did spirometry to obtai the baselie forced expiratory volume i oe secod (FEV1). After both exercise challeges all subjects did serial spirometry ad the lowest FEV1 recorded over time was used to calculate the fall i FEV1 expressed as a percetage of the measured pre-exercise (baselie) value (% fall i FEV1) ad the area above the FEV1 curve (AAC 0 30 mi ) expressed as a percetage of the pre-exercise value. Chages i both exercise variables were also aalysed i percetile subgroups defied by questioaire aswers o habitual physical activity i hours. The mea % fall i FEV1 was sigificatly higher for treadmill exercise tha for the step test ( versus ); ad the AAC 0 30 mi was larger for treadmill tha for the step test ( % versus % mi). I all subgroups defied by habitual physical activity the mea % fall i FEV1 decreased more after treadmill exercise tha after the step test. After step test ad treadmill exercise o sigificat correlatio was foud betwee % fall i FEV1 ad baselie lug fuctio, or betwee % fall i FEV1 amog groups defied by habitual physical activity. Although the 3-mi step test yields a lower % fall i forced expiratory volume i oe secod (FEV1) ad a lower value of the area above the FEV1 curve tha treadmill testig, it is a quick, ecoomical, reproducible ad portable alterative procedure for idetifyig exercise-iduced asthma i outpatiets ad epidemiological studies. Baselie lug fuctio ad habitual physical activity have o ifluece o the amout or duratio of exercise-iduced asthma. Eur Respir J 2004; 23: *Cystic Fibrosis Cetre ad # Allergology ad Immuology, } Paediatric Dept, Uiversity of Rome "La Sapieza", Rome, Italy. Correspodece: G. Tacredi Paediatric Departmet Cystic Fibrosis Cetre Uiversity of Rome "La Sapieza" Viale Regia Elea, Rome Italy Fax: giacarlo.tacredi@uiroma1.it Keywords: Area above the curve 0 30 mi exercise-iduced asthma 3-mi step test treadmill exercise test Received: April Accepted after revisio: November Although may asthmatic subjects fid exercise-iduced asthma (EIA) a problem, childre ad youg adults suffer most from its effects because they egage more ofte i physical activities ad sports. The prevalece of brochial asthma i childre is aroud 10%; ad 40 90% of these patiets have EIA [1, 2], a maifestatio that is frequetly udiagosed [3]. Exercise challege testig to evaluate EIA is helpful i the diagosis ad maagemet of asthma ad is also importat i research studies ivestigatig the efficacy of drug therapy. EIA is defied as a coditio i which physical activity triggers acute airway arrowig i people with heighteed airway reactivity [4]. The diagosis of EIA is suggested by the cliical history ad demostrated by a decrease of 15% i forced expiratory volume i oe secod (FEV1) after a exercise challege, i accordace with the Europea Respiratory Society (ERS) ad America Thoracic Society (ATS) statemets [5, 6]. EIA is usually studied with various ergometers such as the treadmill ad cycloergometer or free ruig. These tests are complex, expesive ad require a large space. For this reaso, a simple, stadardised ad reproducible challege test is eeded to assess the diagosis of asthma ad EIA. The step test, a reproducible test i healthy childre ad cystic fibrosis patiets [7, 8], is used with various protocols, to evaluate physical efficiecy i healthy subjects ad sportsme [9 12]. It is legally compulsory i Italy for all persos wishig to egage i competitive sports [13]. The 3-mi step test is also used to assess exercise capacity i childre with cystic fibrosis [8, 14, 15], to evaluate the effect of a course of itraveous atibiotics o exercise tolerace [16], to study cadidates for lug trasplatatio [17], ad to determie the risk of oxyge desaturatio durig exercise [18]. Few published studies have used the 3-mi step test to assess EIA i asthmatic childre [19 21]. I a study coducted i a small umber of adolescet asthmatic patiets, YOUNG ad HOLST [19] used a fall of 10% i the FEV1, whereas 15% is curretly cosidered a better diagostic value for EIA [5, 6]. I additio, FEINSTEIN et al. [20] studied oly a selected

2 570 G. TANCREDI ET AL. populatio (adolescet Africa-America male football players); ad coducted a epidemiological study without comparig the step test with treadmill exercise [21]. No published study has yet addressed the ifluece of baselie lug fuctio ad habitual physical activity o the presece or severity of EIA or has EIA bee evaluated with area above the curve betwee 0 ad 30 miutes (AAC 0 30 mi ) after the 3-mi step test. The primary aim i this study was to cofirm whether the 3-mi step test effectively detected EIA, ad to compare it with treadmill exercise i a group of asthmatic childre, i view of future applicatios i outpatiets ad epidemiological studies. The study also ivestigated whether baselie lug fuctio ad habitual physical activity ifluece resposes to the two exercise challeges. Patiets Methods Oe hudred ad sixty-ie cosecutive childre attedig the outpatiets cliic at the Departmet of Paediatrics, Uiversity of Rome "La Sapieza", Italy, for respiratory disease durig the 2 yrs from April 2000 to Jue 2002 were erolled. Because all patiets discotiued asthma medicatios before testig, to perform the challege tests uder safe coditios ad i accordace with the ERS ad ATS statemets [5, 6] oly subjects with a ormal FEV1 (o80% of predicted) were studied. Of the 169 childre erolled, 154 subjects (84 male childre, mea age 12.9 yrs, rage: yrs; 70 female childre, mea age 13.1 yrs, rage yrs) etered the study ad 15 were excluded: 11 who failed to complete both tests ad four who had FEV1 values v80% pred. All participats had a cliical diagosis of asthma cofirmed by a o12% improvemet i FEV1 after admiistratio of ihaled salbutamol, accordig to the ATS guidelies 1994 [22]. The study was approved by the Hospital Research Ethics Committee ad parets gave iformed coset. Each subject was evaluated i the Respiratory Pathophysiology Laboratory of the same Departmet. Childre were tested betwee 9:00 to 12:00 h i a climate-cotrolled room (temperature aroud 21uC, humidity aroud 45%). Noe of the childre had experieced acute episodes of asthma or respiratory tract ifectios, or both, i the previous 15 days ad oe had received oral or ihaled b 2 -agoists, chromoes or atihistamiics i the previous 48 h. Oral ad ihaled corticosteroids were withdraw 24 h before testig because their ati-iflammatory effect may decrease brochial resposiveess [5, 6]. Study desig Durig the first visit the study procedures were explaied ad a questioaire was admiistered by a physicia to each child ad their parets. The questioaire sought iformatio o how childre spet their time durig the past week, to evaluate their hours of habitual physical activity [23, 24]. Four subgroups were defied by hours of physical activity (frequecy ad duratio of their participatio i orgaised sports or free but eergetic play, or both): 0 2 h; 3 5 h; 6 9 h; ad h. the mass flow sesor was calibrated every day usig a stadard 3-L syrige takig ito cosideratio room humidity, temperature ad barometric pressure. Baselie (preexercise) variables cosidered were the largest forced vital capacity ad FEV1 obtaied from at least three spirometric tests. Exercise challege Withi a week after erolmet each subject did two exercise challeges i radom order: a treadmill test (Ruer, MTC Climb, Modea, Italy) ad a step test. To avoid a possible refractory period after the first exercise challege the two tests took place o differet weekdays at least 24 h apart. Because the ATS [6] statemet suggests that at least 4 h should elapse betwee repeat testig, istead of takig place i the afteroo, testig took place o the followig morig. To avoid altered brochial resposiveess, subjects who ihaled salbutamol after exercise owig to the oset of asthma were tested at least 24 h after the evet. The iclie ad speed of the treadmill were admiistered accordig to a stadardised protocol for 6 8 mi, to iduce a heart rate v80% of the maximum predicted (y210-age) durig the last 4 mi of the test [6]. Some childre (14 of 154 childre; 6 male), who were overweight ad ufit, ra 6 mi but maitaied their target heart rate for oly 1 mi. For the 3-mi step test, childre stepped up ad dow a 30-cm custom-made sigle step set at a rate of 30 steps per mi for 3 mi, i time with a electroic metroome. For both tests ose clips were applied to esure mouth breathig. The same observer evaluated the two tests i the same subject. Durig both exercises a 3-lead electrocardiogram was recorded (Delta 3 plus; Cardiolie Remco Italia, Mila, Italy) to determie heart rate ad to detect evetual arrhythmias. Arterial oxyge saturatio (Sa,O 2 ) was moitored with a pulse oximeter (Nellcor1; Hayward, CA, USA) through a probe attached to the idex figer. After both tests, FEV1 was measured at least twice, at 1, 5, 10, 15, 20, ad 30 mis after exercise ad the lowest FEV1 recorded over this period was used to calculate the maximal percetage fall from baselie by the followig equatio: % fall i FEV1~(pre-exercise FEV1{ ð1þ lowest FEV1 post-exercise)=pre-exercise FEV1 100 Subjects who reached a % fall i FEV1 o15% were cosidered positive for EIA [5, 6]. The area above the curve (AAC 0 30 mi ) was defied as the area above the FEV1, expressed as a percetage of the pre-exercise value, obtaied up to 30 mi post-exercise, calculated usig liear trapezoidal itegratio [25, 26]. If FEV1 exceeded baselie values, the area was subtracted from the AAC 0 30 mi measuremet with a percetage chage i FEV1. The AAC 0 30 mi therefore provided a sigle umber itegratig the amout ad duratio of brochocostrictio. At the ed of the exercise challege childre who had FEV1 values 10% lower tha baselie, received 200 mg of ihaled salbutamol before they left the laboratory. To assess reproducibility of the 3-mi step test, 43 radomly selected childre (25 male ad 18 female) who had ormal FEV1 (w80% pred) repeated a secod step test o the followig day. Lug fuctio tests Lug fuctio was tested with a ultrasoud flow-meter spirometer (Vmax 229; Sesor Medics Italia, Mila, Italy); Statistical aalysis All values are reported as mea SD. Kedall9s tau-b ad the K statistic to measure agreemet were used to determie

3 EVALUATING EXERCISE-INDUCED ASTHMA 571 the possible correlatio betwee the two challege tests i EIA groups. Paired t-tests were used to evaluate the statistical sigificace betwee the mea values for the two tests. A aalysis of variace (ANOVA) was used to evaluate statistical differece betwee the mea values for each group. Correlatios amog variables were assessed with Pearso9s r or the Spearma9s rak test as appropriate. Blad-Altma9s plot [27] was also used to compare chages i the outcome measures for the two tests. The differece betwee the percetage chage i % fall i FEV1 obtaied by the two tests was plotted agaist their mea values. The mea differece betwee tests, ad the limits of agreemet (defied as 2 SD from the mea of the two tests) were also calculated. p-values v0.05 were cosidered to idicate statistical sigificace. Results All adverse experieces durig ad after exercise challeges were trasiet ad self-limited (cough, chest tightess, wheezig) ad there were o cliically sigificat fidigs o physical examiatio or electrocardiogram. Of the 154 childre erolled, 18 ihaled 200 mg of salbutamol 30 mi after the ed of the exercise challege because their FEV1 values were 10% lower tha baselie. I 12 of the 18 subjects cough or wheeze or both developed durig or immediately after exercise but all these subjects became asymptomatic before leavig the laboratory. Noe of the subjects with a ormal FEV1 after exercise had tight chest or wheezig after exercise. Before ad durig the two tests, all subjects had ormal Sa,O 2 values (rage %). The mea heart rate values reached at the ed of exercise challeges were higher after treadmill testig tha after the step test ( versus beats per miute (bpm); pv by paired t-test). All 154 patiets had FEV1 pre-exercise values o80% pred. Mea baselie pre-exercise FEV1 values were similar before both challege tests (step test: ; treadmill %, p=ns). I 85 of the 154 childre studied (55.2%) both tests iduced EIA ad i 55 childre (35.7%) both tests were egative. Of the remaiig 14 childre, 12 subjects had EIA after treadmill testig but ot after the 3-mi step test ad oly two subjects had EIA after the step test but ot after treadmill exercise. Kedall tau-b correlatio showed a sigificat relatioship betwee the two tests (tau-b coefficiet, 0.82; pv0.001; table 1). Data for the 43 childre who had completed the secod step test showed that the 3-mi step test yielded reproducible data. O the two occasios o sigificat differece i maximal heart rate (1u step test versus 2u step test: ; bpm, p=ns by paired t-test) ad % FEV1 fall (1u step test versus 2u step test: ; %, p=ns by Table 1. The presece of exercise-iduced asthma (EIA) after treadmill exercise ad the 3-mi step test i the 154 asthmatic childre Treadmill paired t-test) was observed ad Kedall tau-b correlatio showed a sigificat relatioship betwee the two tests (tau-b coefficiet, 0.90; pv0.0001). There was o sigificat differece i the umber of subjects who had EIA i both tests: 25 of 43 (58.1%) childre i the first test ad 24 of 43 (55.8%) i the secod. The Blad-Altma plot comparig chages i the outcome measures for the two step tests showed that the mea differece i % fall i FEV1 were low betwee the two tests ( %), with small limits agreemet (-4.5% ad z5.9%). The 3-mi step test yielded high diagostic power i compariso with the treadmill test (sesitivity: 87.6%; 95% cofidece itervals (CI): ad specificity: 96.5%; 95% CI: ) ad good positive ad egative predictive values (97.7%; 95% CI: ad 82.1%; 95% CI: ). No sigificat differece was foud i baselie lug fuctio, age, height or habitual physical activity betwee the 12 subjects (3 male childre) with EIA iduced oly by the treadmill ad the others. But their mea maximum heart rate values reached at the ed of the step test were sigificatly lower tha those of the other subjects ( versus bpm, pv0.002 by upaired t-test). The % fall i FEV1 was greater after treadmill exercise tha after the step test ( versus %; pv0.001 by paired t-test); ad a sigificat relatioship was foud betwee the two tests (Pearso9s r=0.81; pv0.001). After exercise testig, with the exceptio of the % FEV1 of baselie (pre-exercise) values determied i the first miute, all values for this variable assessed at the other time poits (5, 10, 15, 20, ad 30 mi after testig) were sigificatly higher after treadmill exercise tha after the 3-mi step test. I both tests, the % fall i FEV1 reached maximum at 5 mi (fig. 1). Treadmill testig yielded a sigificatly larger AAC 0 30 mi tha the step test ( % versus % mi; pv0.001 by paired t-test) (fig. 2). For each group defied i percetiles of habitual physical activity the mea % fall i FEV1 was sigificatly higher after treadmill testig tha after the step test. Subjects with fewer hours of physical activity (0 2) had a higher % fall i FEV1 after the treadmill test tha after the step test. No sigificat differece was foud i the % fall i FEV1 mea values withi the four physical activity groups for the step test (pv0.2) or treadmill test (pv0.09) (table 2). Nor did the baselie FEV1 (% pred) value correlate sigificatly with degree of % fall i post-exercise FEV1 i either test (treadmill r=-0.03, p=ns; step-test: r=0.14, p=ns). FEV1 % pred NS *** *** * *** *** EIAz EIA- All subjects Step test EIAz (56.5%) EIA (43.5%) All subjects 97 (63%) 57 (37%) Time after exercise mi Data are preseted as umber ad percetage of subjects with exerciseiduced asthma (EIAz: % fall i forced expiratory volume i oe secod (FEV1) o15; EIA-: % fall i FEV1 v15). Fig. 1. Forced expiratory volume i oe secod (FEV1) (% pred) after the treadmill test (%) ad the 3-mi step test (&). NS: osigificat; *: pv0.05; ***: pv0.001.

4 572 G. TANCREDI ET AL. % Fall i FEV # Miutes after exercise % fall i FEV1 (differece) % fall i FEV1 (mea of two tests) Fig. 2. The area above the forced expiratory volume i oe secod (FEV1) time curve from 0 to 30 mi (AAC 0 30 mi ) after exercise i the two tests. Treadmill (&): % mi; step test (&): % mi (pv0.001 by paired t-test). # : ed of exercise. The Blad-Altma plot comparig chages i the outcome measures for the two tests showed that the % fall i FEV1 differed markedly betwee the two tests ( %), with large limits of agreemet (-5.5% ad z12.1%) (fig. 3). I both tests, FEV1 decreased by a mea %. I the group of subjects with a mea % fall i FEV1 of w10%, more subjects had a greater fall i FEV1 with the treadmill exercise test tha with the 3-mi step test (83/97, 85.6% versus 14/97, 14.4%). Discussio Although the 3-miute step test was quick ad simple to perform i the asthmatic childre that were studied, it was less effective tha the treadmill test i detectig EIA (97/154 childre versus 87/154), as cofirmed by the sigificatly lower AAC 0 30 mi (fig. 2) i the step test tha i the treadmill test ad the Blad-Altma plot (fig. 3). A possible reaso why the two tests differed is that because the step test has a short duratio, childre reached ad maitaied a higher maximal heart rate after treadmill exercise tha after the step test (pv0.0001). Presumably for this reaso, the 12 childre i whom EIA developed after the treadmill test but ot after the step test had a lower maximal heart rate after the step test tha the whole study sample. I accordace with the literature, the curret authors cofirmed that EIA is effort depedet, hece reproducible results deped also o a stadardised exercise load [28]. I the step test the itesity ad duratio of exercise is therefore predetermied (3 mi), whereas the treadmill test lasts at least 6 mi ad therefore allows subjects to reach higher miute vetilatio, oe of the major causes of EIA. Fig. 3. Blad-Altma plot of the percetage differece i the % fall i forced expiratory volume i oe secod (FEV1) betwee the two tests (treadmill mius step test) compared with their mea values. The mea differece of % fall i FEV1 is represeted as a ubroke lie. The limits of agreemet (dashed lies) are defied as 2 SD from the mea differece of % fall i FEV1. Each poit i the figure may represet oe or more overlappig cases. The 3-mi step test evertheless yielded high diagostic power ad good positive ad egative predictive values i compariso with the treadmill test i detectig EIA i asthmatic childre. A possible way of improvig eve further the diagostic sesitivity of the 3-mi step test is to icrease its duratio (5 6 mi), to maitai the target heart rate (80% pred) for loger. But this solutio to the problem would mea foregoig oe of the test9s great advatages, its shortess. The target heart rate could also be icreased ad maitaied by leavig the duratio of the test uchaged ad istead, raisig the rate of steppig. Yet this solutio has the disadvatage of makig the step test more difficult to perform. As a alterative the curret authors suggest icreasig the height of the platform i relatio to the childre9s height. This adjustmet (40 50 cm) has already bee recommeded by the Italia law cocerig step tests for adults wishig to begi competitive sports [13]. I the curret study sample the 3-mi step test also produced reproducible results, as others have reported [8]. Moreover, eve if it decreases test sesitivity, performig exercise testig i a climate-cotrolled room, as i the curret study, reduces variability related to temperature ad humidity sice cold air ad dry ambiet air (with low relative humidity, f50%) icrease airways hyperresposiveess. Although the fidigs of the curret study suggest that the 3-mi step test is less sesitive tha treadmill testig i provokig EIA i asthmatic childre (87/154 versus 97/154; table 1), whe treadmill testig is ufeasible because of expese ad complexity it may be used as a alterative to the exercise test. The free ruig test is also widely used as a Table 2. Study populatio grouped accordig to their habitual physical activity Habitual physical activity h No. of subjects Treadmill % fall i FEV1 Step test % fall i FEV1 p-value v v v v0.004 v0.09 } v0.2 } Data are preseted as mea SD; p-values by paired t-test betwee two tests (treadmill or step test); } : a aalysis of variace (ANOVA) was used to compare habitual physical activity i hours i the four groups for the same test (treadmill or step test).

5 EVALUATING EXERCISE-INDUCED ASTHMA 573 exercise test istead of the treadmill test i epidemiological studies. But it requires more space uless it takes place i a idoor gymasium, is sometimes uavailable i outpatiet or public settigs ad is ot reproducible i the commuity settig [29]. Hece KUKAFKA et al. [30] assert that more data are eeded o the effectiveess of free ruig as a "field test" i epidemiological studies i patiets with asthma. Coversely, HABY et al. [31] cosider a 6 mi ru o a 50- or 100-m track o the flat to have good validity ad reliability whe performed uder appropriate coditios (usig oseclips to esure mouth-breathig ad moitorig heart rate to maitai a heart rate of bpm for the fial 4 mi of exercise). Hece they coclude that a 6-mi free ruig challege test could be used as a stadardised tool i epidemiological studies. Support for the 3-mi step test as a alterative to the treadmill test comes from a study by FEINSTEIN et al. [20] who showed that the step test is more sesitive tha physical examiatio, pre-exercise pulmoary fuctio testig ad self-admiistered questioaire i idetifyig EIA i adolescet athletes ad i elemetary schoolchildre. I their study of 32 adolescet asthmatic patiets, YOUNG et al. [19] reported a fall of w10% i FEV1 i 27 subjects after the treadmill test ad i 25 after the step test. They also observed a strog correlatio betwee the maximum % fall i FEV1 after the two exercise challeges (r=0.92; pv0.0001). I 11 patiets, the patiet9s history of EIA agreed poorly with the asthmatic symptoms maifested after exercise testig. Sice 1982, the step test together with lug fuctio testig ad electrocardiogram before ad durig exertio has bee compulsory i Italy for all persos wishig to egage i competitive sports [13]. The results of the curret study ow suggest that spirometric testig at 5 ad 10 mi after the 3-mi step test, to idetify a fuctioally importat decrease i FEV1, would help i detectig urecogised EIA. Accordigly, i the curret authors9 experiece i a academic paediatric departmet, amog 200 healthy childre referred for exercise testig before egagig i sports activities, w5% have EIA. Iteratioal guidelies of asthma recommed that childre with documeted EIA should receive a adjuctive dose of ihaled b 2 -agoists or chromoes before startig physical activity [32]. Asthma has a high prevalece i Europea coutries, about 10 12% of the childhood populatio. The prevalece of EIA is also much higher i subjects who take part i sport at elevated workloads i cold eviromets: ice hockey players (21%) [33], cross coutry skiers (31%) [34], ad figure skaters (55%) [35]. The preset study also ivestigated whether baselie lug fuctio iflueces resposes to step test ad treadmill exercise. I either test did baselie FEV1 values, expressed as % pred, correlate either with the presece or the severity of EIA (% fall i FEV1). All the childre studied had baselie FEV1 values betwee % pred. I cotrast, studyig childre with mild-to-moderate asthma LINNA [36] observed a egative correlatio betwee baselie flow values ad the respose to exercise. I aother study CABRAL et al. [37] foud that although the prevalece of EIA is greater i childre with more severe asthma, the respose to exercise ca be abset eve i childre with severe persistet asthma. The itesity of the exercise-iduced respose is ot cosistetly related to the cliical severity of asthma. CABRAL et al. [37] therefore cocluded that the pre-exercise FEV1 predicts either the severity of respose or the presece of EIA. Aother distictive ad partly uexpected fidig from the curret study is that the level of habitual physical activity was ot related to the presece of EIA i either exercise test. Although i each of the four groups the % fall i FEV1 was statistically higher for the treadmill test tha for the step test, the mea % fall i FEV1 did ot differ statistically i subjects with higher or lower levels of habitual physical activity. All subjects, especially those who were less physically active (0 2 h) evertheless had a higher % fall i FEV1 after treadmill testig tha after the 3-mi step test (17.5% 8.4 versus , pv0.001 by paired t-test). Published reports suggest that the level of cardiorespiratory fitess has o ifluece o EIA [38]. I particular, ormal cardiovascular fitess does ot prevet EIA. Although physical traiig icreases the aerobic capacity similarly i asthmatic patiets ad i healthy subjects, it has o detectable ifluece o the degree of EIA [39]. Coversely, a prologed warm-up period of submaximal exercise ca iduce refractoriess of EIA without iducig brochocostrictio [40, 41]. Oe of the prerequisites of a exercise challege test is safety. Noe of the asthmatic patiets had severe adverse evets (persistet cough, wheezig or dyspoea) after treadmill testig or the 3-mi step test. The step test proved a safe ad valid techique for evaluatig the risk of oxyge desaturatio i patiets with chroic lug disease ad a low lug diffusig capacity for carbo mooxide. I a series of 8,000 patiets o complicatios (symptoms of cardiovascular collapse) developed, eve though half the patiets were elderly ad therefore had a relatively high prevalece of cardiovascular disease. Other studies reported o major problems with step tests [18]. I coclusio, eve if the step test causes a lower % fall i forced expiratory volume i oe secod tha the treadmill test i asthmatic childre, it is a quick, ecoomical, reproducible, safe ad portable alterative procedure that ca be useful for idetifyig exercise-iduced asthma or brochial asthma i outpatiets ad epidemiological studies. 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