Activity-related dyspnoea is the most common symptom of patients with chronic lung diseases and underpins perceived poor health status. Our understanding of the nature and source of dyspnoea continues to grow but successful amelioration of this distressing symptom can remain elusive, especially in those with advanced lung diseases. According to Norman Jones, the great Canadian physiologist, “breathlessness can be seen to result from an imbalance between the demand for breathing and the ability to achieve the demand.” Indeed, in most clinical situations where patients report severe dyspnoea, ventilatory demand-capacity imbalance is present. Thus, in patients with chronic lung conditions, ventilatory demand reaches or exceeds maximal ventilatory capacity (MVC) during physical exertion. Similarly, the ratio of respiratory muscle effort (measured by esophageal manometry) to maximal possible respiratory effort is increased at a given work rate or ventilation in patients with lung disease versus healthy controls.