Bio-impedance analysis for appendicular skeletal muscle mass assessment in (pre-) frail elderly people

Screening populations for skeletal muscle mass (SMM) is important for early detection of sarcopenia. Our aim was to develop an age specific bio-impedance (BI) prediction equation for the assessment of appendicular skeletal muscle mass (ASMM) in (pre-) frail elderly people aged 65 and older.

Anthropometric, BI and dual-energy X-ray absorptiometry (DEXA) measurements from 106 (pre-) frail elderly subjects (61 females and 45 males, aged 65-96 years) were used to derive three ASMM prediction equations using multiple regression analysis: one for single frequency BI measurements at 50 kHz (ASMM_50kHz), one for measurements at the characteristic frequency (ASMM_Fc) and one for bioelectrical impedance spectroscopy (ASMM_BIS). The same data was used to evaluate an existing prediction equation.

ASMM_50kHz had the best fitting model (r²_adj = 0.923, SEE = 1.19 and a PRESS value = 163.4), followed by ASMM_Fc (r²_adj = 0.915, SEE = 1.25 and a PRESS value = 175.9) and ASMM_BIS (r²_adj = 0.915, SEE = 1.26 and a PRESS value = 177.1). Average ASMM measured by DEXA and both ASMM_{50kHz and} ASMM_Fc were comparable. ASMM_BIS tended to underestimate ASMM slightly. An existing prediction equation had a tendency to underestimate ASMM in people with a lower amount of ASMM and overestimate ASMM in people with a higher amount of ASMM.

ASMM_50kHz was able to measure average ASMM within our population of (pre-) frail elderly in a valid way. However, its predictive power on both individual and population level needs to be confirmed in an independent and larger (pre-) frail elderly population and across multiple institutions and ethnic groups.