Sex and population-specific cutoff values of muscle quality index: Results from NHANES 2011-2014

Background & aims: Muscle quality index (MQI) is used to measure the quality of the muscles. It is defined as the ratio of muscle strength per unit of muscle mass, but since this might vary by rage and ethnicity, we aimed to develop sex, and population-specific normative data and cutoff values for MQI (extremally low and low) using the arm or appendicular skeletal muscle mass (ASM) obtained from a population-representative sample.

Methods: This cross-sectional analysis included data from 4849 volunteers (aged 20-59 years) from the National Health and Nutrition Examination Survey (NHANES) 2011-2014. Measures of handgrip strength (HGS) were performed using a hand dynamometer. ASM was assessed by dual-energy X-ray absorptiometry (DXA). Arm ASM mass was used to calculate MQI_Arm [dominant HGS/dominant arm ASM (kg/kg)]; ASM was used to calculate MQI_App [dominant HGS/ASM (kg/kg)]; and the sum of the non-dominant hand and dominant hand were used to calculate MQI_total [HGS sum/ASM (kg/kg)]. Cutoff values were derived from a young reference subgroup (n = 1625 aged, 20-39 years), with low and extremely low MQI defined as 1 and 2 sex-specific standard deviations below the mean, respectively.

Results: MQI_Arm, MQI_App, and MQI_Total differed by sex and population studied. Overall, using the proposed cutoffs, men showed lower values of MQI_Arm than women, and higher MQI_App, and MQI_Total values. Compared to non-Hispanic Whites, non-Hispanic Asians had higher values of MQI while non-Hispanic Black people had lower values.

Conclusion: MQIs cutoffs were established for both sexes and different populations studied. MQI_Arm, MQI_App, and MQI_Total values were lower after the fifth-decade in men, but not in women.