We investigated the effects of ageing on the elastic properties of lung tissue and the chest wall, simultaneously quantifying the contribution of each component to static inspiratory muscle work in resting and exercising adults. We further evaluated the interaction of ageing and habitual physical activity on respiratory mechanics. Static lung volumes and elastic properties of the lung and chest wall (pressure-volume relaxation manoeuvres) in 29 chronically-sedentary and 29 habitually-active subjects, grouped by age, were investigated: young (Y: 20-30 y), middle-aged (M: 40-50 y), older (O: >60 y). Using static pressure- volume data, we computed the elastic work of breathing, including inspiratory muscle work, over resting and exercising tidal volume excursions. Elastic work of the lung (Y=0.79 ±0.05; M=0.47 ±0.05; O=0.43 ±0.05 J.l^-1) and chest wall (Y=-0.49 ±0.06; M=-0.12 ±0.07; O=0.04 ±0.05 J.l^-1) changed significantly with age (P<0.05). With ageing, a parallel displacement of the chest-wall pressure-volume curve resulted in a shift from energy being stored primarily during expiration, to energy storage during inspiration, and driving expiration, both at rest and during exercise. While deviating significantly from young adults, this did not significantly elevate static inspiratory muscle work, but resulted in a redistribution of the tissues on which this work was performed, and the phase of the respiratory cycle in which it occurred. Nevertheless, static inspiratory muscle work remained similar across age groups, at rest and during exercise, and habitual physical activity failed to influence these changes.