Muscle quality index comparisons between Hispanics and non-Hispanic Caucasians using dual energy X-ray absorptiometry and handgrip strength

Muscle quality index (MQI) can be computed in various ways. Also, many studies have evaluated MQI in older adults and non-Hispanic populations. The aim of this study was to compare various muscle quality indexes between Hispanics and non-Hispanic Caucasians when stratifying grip strength and appendicular lean mass measurements. 235 participants (aged 25.5 ± 9.5 for males and 26.4 ± 9.9 for females) completed a dual energy X-ray absorptiometry (DXA) scan to assess appendicular lean mass (ALM). Handgrip strength (HGS) was assessed using a handheld dynamometer. MQI was computed using four different models: 1). MQIRA: ALM and HGS of right arm and hand, respectively; 2). MQILA: ALM and HGS of left arm and hand, respectively; 3). MQIARMS: ALM and HGS of both arms and hands, respectively; and 4). MQITOTAL: ALM of upper and lower-limbs and HGS of left and right hand. Hispanic males and females exhibited lower HGS compared to Caucasians with effect sizes ranging from trivial (d = 0.17) to moderate (d = 0.80). Females demonstrated higher MQI values compared to males for MQIARMS (d = 0.70), MQIRA (d = 0.75), and MQILA (d = 0.57). However, MQITOTAL yielded a small practical effect (d = 0.33) in favor of males (3.2 ± 0.5 kg/kg vs. 3.1 ± 0.5 kg/kg). After factoring by sex and ethnicity, Hispanic males and females, compared to non-Hispanic Caucasians males and females, showed trivial-to-small practical differences (d values ranging from 0.03 to 0.39). These results demonstrate MQI models vary across sex, particularly when utilizing models that account for upper extremity strength and ALM (i.e., MQIARMS, MQIRA, and MQILA). Lastly, to establish consistency in future research, the present study recommends using MQI models that account for ALM of upper- and lower-limbs (i.e., MQITOTAL). However, research measuring muscular strength via one upper-limb (e.g., left hand) might consider measuring ALM of the corresponding arm (e.g., left arm) when computing muscle quality (e.g., MQILA).