Raw BIA variables are predictors of muscle strength in patients with chronic obstructive pulmonary disease

Although loss of fat-free mass (FFM) and reduced muscle strength are highly prevalent in chronic obstructive pulmonary disease (COPD), only few data are available on the relationships of handgrip strength (HGS) and respiratory muscle strength with body composition in such disease. In particular, we aimed to assess whether raw bioelectrical impedance (BIA) variables were independent predictors of muscle strength in COPD patients, possibly more significant than anthropometric variables and BIA-based estimates of FFM.

Two hundred and thirty-seven COPD patients (161 males and 76 females) underwent respiratory, anthropometric, BIA, HGS and respiratory muscle strength (maximum inspiratory or expiratory pressure=MIP and MEP) measurements. Bioimpedance index (BI index=height square/whole-body impedance) and phase angle (PhA) were considered as raw BIA variables. FFM was estimated using three disease-specific BIA equations.

In COPD patients a stronger correlation was observed between HGS and PhA compared to the ones with anthropometric variables or FFM estimates. Multiple regression analysis showed that combining BI index and PhA (plus age in male patients) accounted for 50.2% and 42.6% of the variance in HGS in male and female patients, respectively. Similarly, BI index and PhA emerged as predictors of both MIP and MEP in males, while in females MIP was related only to PhA and MEP only to BI index.

Raw BIA variables are independent and valuable predictors of HGS and respiratory muscle strength in COPD patients. BI index and PhA could provide useful information for evaluating body composition and better assessing muscle strength and physical fitness in COPD.