Association of fat mass index versus appendicular lean mass index with physical function - The Yishun Study

Background: Increase in body fat and reduced muscle mass are common body composition changes with age and precedes functional impairment. However, it remains unclear whether increased adiposity or less lean mass is a stronger determinant of worse functional performance. This study compared the association between fat versus lean mass indices with physical function among community-dwelling adults after adjusting for age and muscle strength. Methods: 542 community-dwelling adults aged between 21 and 90 years were recruited. All participants were assessed for body composition (dual X-ray absorptiometry), knee extensor strength (KES) and physical function. Fat mass and lean mass (weight in kg) were adjusted by height (in meters) squared - measured as fat mass index (FMI) and appendicular lean mass index (ALMI), respectively. Physical function was assessed using the Short Physical Performance Battery (SPPB) and the timed up and go (TUG) test. Results: FMI was significantly associated with both SPPB (ss = -0.130, p = 0.019) and TUG (ss = 0.182, p < 0.01) after accounting for ALMI and other covariates. This association was moderated by age and KES. FMI was associated with SPPB and TUG in individuals who are older or with weaker KES. While ALMI was found to be significantly associated with TUG (ss = 0.121, p = 0.023), no significant association was found between ALMI and physical function after accounting for FMI. Conclusions: Our results show that FMI is a stronger determinant of physical function than ALMI. This emphasizes the importance of reducing body fat to mitigate functional decline especially in older and weaker adults.