Figure 2. Work of breathing and chest wall volume changes during exercise and isocapnic resting hyperpnoea.

Changes (relative to values at end-expiration at lowest ventilation) in work of breathing (A) rib cage (B) and the abdominal (C) volume at the end of inspiration and expiration at different levels of minute ventilation during exercise (open triangles) and isocapnic, resting hyperpnoea (filled triangles). Values are means ±s.e.m. for 10 subjects. Asterisks denote significant differences between the exercise and hyperpnoea tests (P < 0.05).