To adequately respond to the metabolic demand during exercise, the respiratory system has to closely regulate the ventilatory and the cardiovascular systems.

After a brief description of the anatomy of lungs, pleura, thoracic cage, and respiratory muscles, the attention is focused on the mechanics of breathing.

The second part of the chapter is devoted to the mechanics of breathing. In other words, the questions are: what are the strengths able to deform the rib cage and how are they exerted on the lungs, generating flow and volume changes?

The first part of this section defines pressures (pleural, alveolar, intra-thoracic, and trans-thoracic pressures), flows, and volumes, and their respective ratios (i.e. volume/pressure and flow/pressure curves), to explain the effects of compliance (of lung, thorax, and respiratory system) and resistance (of airways, or respiratory tissues) on respiratory movements and ventilation. In a second part, classical representations of spirometry are introduced, as well as representations of the volume/pressure, flow/volume, during both tidal ventilation and ventilation during exercise.