Prior studies have shown that the intensity influences the sensitivity of exercise challenge tests (ECT) and that a heart rate-based protocol does not ensure sufficient exercise intensity to induce bronchoconstriction. It is not common clinical practice to perform a pre ECT to establish maximal heart rate or maximal oxygen uptake. The heart rate formula recommended by ATS (HRmax= 220−age) is usually applied to determine recommended intensity of the ECT. Conducting a second ECT, based on the knowledge of the first test, introduce the possibility to adjust the intensity on an individual basis. In addition, based on clinical experience, patients may seem reluctant to perform maximal the first time they undergo an ECT on a treadmill. The hypothesis is that patients are less reluctant to perform maximal the second time they undergo the test when they are more accustomed to the procedure and the treadmill by itself.