Abstract
Muscle quality is well-known to decrease with aging and is a risk factor for metabolic abnormalities. However, there is a lack of information on race-associated differences in muscle quality and other neuromuscular features related to functional performance. This study aimed to compare muscle quality, function, and morphological characteristics in Japanese and Brazilian older individuals. Eighty-four participants aged 65–87 years were enrolled in the study (42 Japanese: 23 men, 19 women, mean age 70.4 years; 42 Brazilians: 23 men, 19 women, mean age 70.8 years). Echo intensity (EI) and muscle thickness (MT) of the quadriceps femoris were measured using B-mode ultrasonography. A stepwise multiple linear regression analysis with EI as a dependent variable revealed that MT was a significant variable for Japanese participants (R2 = 0.424, P = 0.001), while MT and subcutaneous adipose tissue (SCAT) thickness were significant variables for Brazilian participants (R2 = 0.490, P = 0.001). A second stepwise multiple linear regression analysis was performed after excluding MT and SCAT thickness from the independent variables. Sex and age for Japanese participants (R2 = 0.381, P = 0.001) and lean body mass and body mass index for Brazilian participants (R2 = 0.385, P = 0.001) were identified as significant independent variables. The present results suggest that MT is closely correlated with muscle quality in Japanese and Brazilian older individuals. Increases in muscle size may induce decreases in intramuscular adipose tissue and/or connective tissues, which are beneficial for reducing the risks of metabolic impairments in Japanese and Brazilian older individuals.
Highlights
Aging is an irreversible physiological phenomenon that causes functional impairments and morphological changes in skeletal muscle
Japanese participants had smaller body mass index (BMI) (Japanese: 22.4 ± 2.7 kg/ m2; Brazilians: 27.4 ± 2.9 kg/m2; P = 0.001), abdominal girth (Japanese: 85.2 ± 8.2 cm; Brazilians: 99.8 ± 11.7 cm; P = 0.001), %body fat (Japanese: 27.8 ± 7.3%; Brazilians: 37.7 ± 7.3%; P = 0.001), and lean body mass (LBM) (Japanese: 35.2 ± 12.1 kg; Brazilians: 46.4 ± 10.5 kg; P = 0.001) than Brazilian participants
LBM and BMI are indices of skeletal muscle mass and degree of obesity, respectively. These indices were expected to be alternative parameters for the independent variables selected in the first step, i.e. muscle thickness (MT) and subcutaneous adipose tissue (SCAT) thickness. These results clearly showed that the amounts of muscle (LBM) and adipose tissues (BMI or abdominal girth) had strong effects on Echo intensity (EI) of the quadriceps femoris (QF) in Brazilian participants (Table 2)
Summary
Aging is an irreversible physiological phenomenon that causes functional impairments and morphological changes in skeletal muscle. Muscle quality of Japanese and Brazilian older individuals [1], the reduction in cross-sectional area of the vastus lateralis (VL) muscle was up to 1% per year after 50 years of age. In a 12-year longitudinal study by Frontera et al [2], the quadriceps femoris (QF) cross-sectional area decreased by 10.3%, reflecting an annual reduction of 0.9%. These studies clearly showed that aging has a large impact on skeletal muscle quantity. A cohort study involving a large population identified an association between age-related functional deterioration of skeletal muscle and mortality [3]
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