Physical activity decline is disproportionate to decline in pulmonary physiology in IPF

Patients with idiopathic pulmonary fibrosis (IPF) have reduced levels of daily physical activity (DPA); however, little is known about how DPA changes as disease progresses. We aimed to (i) describe change in DPA over 12 months, (ii) analyse its association with conventional markers of disease severity and quality of life and (iii) assess DPA as a prognostic tool.

A total of 54 patients with IPF had DPA monitored at baseline and at 6 and 12 months with a SenseWear armband for 7 consecutive days. Participants completed the Hospital Anxiety and Depression scale, St George's Respiratory Questionnaire and Leicester Cough Questionnaire at each time point and provided clinical data including forced vital capacity (FVC), diffusion capacity of carbon monoxide and 6-min walk distance (6MWD).

Baseline and 12-month daily step count (DSC) were 3887 (395) and 3326 (419), respectively. A significant reduction in DSC (mean = 645 [260], p = 0.02) and total energy expenditure (mean = 486 kJ [188], p = 0.01) was demonstrated at 12 months. The decline in DSC over 12 months was proportionally larger than decline in lung function. Annual change in DPA had weak to moderate correlation with annual change in FVC % predicted and 6MWD (range r = 0.34-0.45). Change in physical activity was not associated with long-term survival.

In IPF, decline in DPA over 12 months is significant and disproportionate to decline in pulmonary physiology and may be a useful tool for assessment of disease progression.