Static Lung Functions: besides physiological measurements, help in the diagnosis of underlying lung disease. It can be used to determine the severity of respiratory muscle involvement in neuromuscular disease, and can guide treatment decisions in several diseases too. This is a pioneering study to assess the correlation of fat free mass index(FFMI) with the static lung function instead of Body Mass Index(BMI). BMI can be misleading as it does not distinguish between the fat & muscle compartment.  So, the aim of our study is to establish that FFMI should be used as reference variable for assessment of static lung functions rather than BMI.