Preface The majority of diseases and pathological conditions reduce physical capacity, which may have an influence on every day life. This is particularly the case for individuals suffering from respiratory diseases that frequently lead to symptoms during physical activity. The symptoms that usually reduce physical performance are leg fatigue, pain and dyspnoea the latter is the most common in respiratory diseases. Dyspnoea is a subjective feeling of not getting enough air and constitutes a disabling symptom, which may severely circumscribe physical activity in patients with pulmonary diseases. As there is no specific available treatment for dyspnoea, it has to be alleviated by treatment of the underlying disease. As dyspnoea is connected with physical activities, it is crucial to understand the mechanisms and the methodology for assessing symptoms associated with exercise when diagnosing and monitoring patients with respiratory diseases we often have to rely on surrogate markers. The exercise test constitutes a possibility to directly assess the physical capacity, thus providing a good insight into how the disease influences physical performance. Therefore, the exercise test is a valuable tool in diagnosing and staging disease severity, and as a guide for pharmacological and nonpharmacological treatment and action plans. In order to obtain a comprehensive view of the nature of reduced physical capacity the exercise test has to be adjusted to the individual issue with questions relating to the patient. Exercise tests have been used for a long time as diagnostic tools for cardiac diseases. During recent years they have become more widely recognised as valuable instruments in the diagnosis and monitoring of pulmonary disorders. In the present issue of the European Respiratory Monograph, cardiopulmonary exercise testing for cardiac and pulmonary diseases has been presented. Techniques and equipment as well as reference values have been thoroughly described. The specific questions that arise in children have been addressed and exercise testing as a tool for the assessment of prognosis and treatment effects has been exhaustively presented. It is now 10 years since the last European Respiratory Monograph on exercise testing was published. This area has developed and there is a lot of new information, in particular regarding physical activity and exercise physiology associated with chronic obstructive pulmonary disease. Therefore, it is timely to update the knowledge in this field and to publish an issue of the European Respiratory Monograph that will be helpful to clinicians, physiologists, nurses, physiotherapists and other professionals interested in exercise physiology and testing. K. Larsson Editor in Chief Eur Respir Mon, 2007, 40, vii. Printed in UK - all rights reserved. Copyright ERS Journals Ltd 2007 European Respiratory Monograph ISSN 1025-448x. vii