ABSTRACT
In the previous edition of this book, we included in our review the factors setting the demand for ventilation during exercise, including metabolism, the control of breathing, and the efficiency of gas exchange. For the present edition we feel that this material is redundant because these factors have been reviewed in many chapters of the present volume and others published in the intervening 10 years (Jones, 1991 ). This allows us to concentrate on the other aspects of the behavior of the thorax during exercise, some of which we believe are not generally appreciated. Specifically, we will explore the notion that respiratory muscle fatigue frequently limits exercise in both health and disease. The demonstration by Roussos and Macklem (1977) that the respiratory muscles, specifically the inspiratory muscles, are prone to fatigue has changed the way we look at ventilation during exercise even in normal subjects. The time to partial failure of force generation decreases as the demand on striated muscle approaches capacity. The demand on the respiratory muscles during exercise is generally felt to be nonfatiguing because the forces involved are thought to be submaximal and because the respiratory muscles are thought to be less fatiguable than other skeletal muscles.
