Locomotor muscle dysfunction and rehabilitative exercise training in fibrotic interstitial lung disease: Where are we at and where could we go?

Exercise limitation is a cardinal feature of fibrotic interstitial lung disease arising from pulmonary gas exchange, respiratory mechanical and cardio-circulatory abnormalities. More recently, it has been recognized that impairment in locomotor muscle function (e.g., reduced muscle mass/strength or heightened fatigability) might also play a relevant contributory role. Exercise training as part of pulmonary rehabilitation is the most effective intervention to improve exercise tolerance, dyspnoea and quality of life in patients with fibrotic interstitial lung disease. Given that exercise training has modest effects on exertional ventilation, breathing pattern and respiratory muscle performance, improvement in locomotor muscle function is a key target for pulmonary rehabilitation in these patients. In the present narrative review, we initially discuss whether the locomotor muscles of patients might be exposed to negative risk factors. After offering corroboratory evidence on this matter (e.g., oxidative stress, inflammation, hypoxia, physical inactivity and medications), we outline their effects on skeletal muscle mass and functional properties. We finish by addressing the potentially beneficial effects of rehabilitative exercise training on these muscle-centred outcomes, providing perspectives to facilitate or optimize the muscle benefits derived from this intervention. This narrative review, therefore, provides an up-to-date outline of the rationale for rehabilitative approaches focusing on the locomotor muscles in this patient population.