Abstract
[Purpose]Declining muscle strength and function are hallmarks of the aging process. This study aimed to determine sex-related differences in myosin heavy chain (MHC) isoforms and muscle mass, strength, and quality with aging.[Methods]This cross-sectional study recruited 53 healthy participants (32 men, 21 women) aged 20–85 years who were divided into four groups: young men (n=17, YM, 29.23±4.51), older men (n=15, OM, 71.87±3.42), young women (n=11, YW, 29.64±4.88), and older women (n=10, OW, 68.1±1.91). Body composition and muscle strength and quality were analyzed. Muscle specimens were obtained from the vastus lateralis in all participants to analyze the type of MHC isoforms.[Results]Men showed a greater age-related decline in skeletal muscle mass (18.6%, p<0.01), lean body mass (10.1%, p<0.05), grip strength (35.3%, p<0.001), isometric strength (29.6%, p<0.001), isotonic power (42.5%, p<0.001), isokinetic strength (up to 44.3%, p<0.001), and muscle quality (up to 24.8%, p<0.01). In contrast, women had significantly lower isometric strength (24.2%, p<0.05), isotonic power (36.5%, p<0.01), and upper-body muscle quality (24.7%, p<0.001) with aging. In addition, the proportion of MHC IIa was significantly lower in OM (p<0.05) and OW (p<0.05) than in YM and YW, respectively. However, the proportion of MHC I was significantly higher in OM (p<0.01) than in YM but was high in both YW and OW. MHC I and MHC IIa negatively and positively correlated, respectively, with muscle strength and function.[Conclusion]These results indicate the existence of sex-related differences in muscle mass, strength, and quality and MHC isoform composition with increasing age. The effects on muscle strength and function with aging were significant in men, but not in women. Higher and lower proportions of MHC I and MHC IIa fibers, respectively, were inversely associated with muscle strength and quality. In particular, Korean YW showed lower muscle strength and quality, and the proportion of MHC isoforms was similar to that in the muscles of OW.
Highlights
Muscle strength normally declines with aging, and its measurement is an important component of physical examination for the evaluation of physical function[1]
We found sex-related differences in body composition (SMM, lean body mass (LBM)), muscle strength, muscle quality, and myosin heavy chain (MHC) isoforms with aging in Korean men and women
Age plays a major role in the correlation between MHC isoforms and body composition and muscle strength and quality in men, but it does not seem to have a significant effect on several measures of muscle parameters in women
Summary
Muscle strength normally declines with aging, and its measurement is an important component of physical examination for the evaluation of physical function[1]. The decline rates of muscle strength after the age of 65 years vary for each individual, it has been reported that an average of 4.5–5.5% of muscle strength is lost every 5 years[2]. Maintenance of muscle mass and strength is an important contributing factor to optimal health and physical functional status in older adults, as the loss in muscle mass and strength with increasing aging results in sarcopenia and increases susceptibility to injury and prevalence of their mobility limitations. Many previous studies have shown sex-related differences in muscle mass, strength, and quality with aging[4,5,6,7,8,9,10,11,12,13,14], few have reported sex-related differences in these muscle parameters in relation to sarcopenia in the Korean population
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