HIF1A and osteoporosis: Further queries are raised regarding the HIF-1α pathway, and physical activity (PA) is proposed as an upstream mechanism for both reduced exercise tolerance and low BMD.<h4>Conclusions</h4>It is suggested that osteoporosis cannot be predicted in a group that is already osteoporotic, and that PA is likely to be the causative mechanism between desaturation in the 6MWT and low BMD in non-cystic fibrosis bronchiectasis.