Measuring Muscle Mass in Adults With Intellectual Disabilities: The Reliability and Construct Validity of Calf...

The amount of muscle mass is an important criterion to diagnose sarcopenia. Two feasible methods for measuring muscle mass in adults with intellectual disabilities (ID) are bioelectrical impedance analysis (BIA) and calf circumference (CC). CC measurements are more accessible, cheaper and easier to use than BIA in adults with ID. This study aimed to investigate the construct validity and intrarater reliability of CC to estimate muscle mass compared to BIA in adults with mild and moderate ID and cardiovascular risk factors (CVRF).

This study was part of the PRET study (NTR, NL8382), which examined the effect of Progressive Resistance Exercise Training on cardiovascular risk factors in 36 adults with ID (55.58 years, SD: 12.89). Construct validity was analysed with Pearson's correlations between CC and BIA measurements (skeletal muscle mass [SMM], segmental muscle mass [SegMM] and skeletal muscle index [SMI]). The intrarater reliability was analysed with the intraclass correlation coefficient (ICC).

The correlation between CC and SMM was 0.19 (95% CI [-0.16, 0.49]), 0.60 (95% CI [0.33, 0.78]) between CC and SegMM and 0.69 (95% CI [0.47, 0.83]) between CC and SMI. The ICC was 0.94 (95% CI [0.89, 0.97]).

The excellent intrarater reliability of CC indicates that CC measurements are reliable within the same assessor for adults with ID and CVRF. However, the use of CC to estimate muscle mass compared to BIA remains questionable.