Mechanisms of exertional dyspnea.

To understand why someone is dyspneic during exercise, we need to follow the advice of Sir Francis Bacon: "No natural phenomenon can be adequately studied in itself alone, but to be understood must be considered as it stands connected with all of nature." In the present context, this implies the careful measurement of events related to metabolism, circulation, and respiration and of the associated sensory events as these systems adapt to the strain and stress of exercise.