Delourme, J., et al. “Six-Minute Stepper Test to Assess Effort Intolerance in Interstitial Lung Diseases”. Sarcoidosis, Vasculitis and Diffuse Lung Diseases, vol. 29, no. 2, Dec. 2012, pp. 107-12, https://mattioli1885journals.com/index.php/sarcoidosis/article/view/2504.