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

Background & aims: 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.

Methods: 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). MQI_RA: ALM and HGS of right arm and hand, respectively; 2). MQI_LA: ALM and HGS of left arm and hand, respectively; 3). MQI_ARMS: ALM and HGS of both arms and hands, respectively; and 4). MQI_TOTAL: ALM of upper and lower-limbs and HGS of left and right hand.

Results: 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 MQI_ARMS (d = 0.70), MQI_RA (d = 0.75), and MQI_LA (d = 0.57). However, MQI_TOTAL 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).

Conclusions: These results demonstrate MQI models vary across sex, particularly when utilizing models that account for upper extremity strength and ALM (i.e., MQI_ARMS, MQI_RA, and MQI_LA). 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., MQI_TOTAL). 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., MQI_LA).