Abstract
Skeletal muscle fibrosis occurs with aging and has been suggested to impair muscle performance, thereby decreasing quality of life. Recently, muscle stiffness, a surrogate measure of muscle fibrosis, was noninvasively quantified as the shear modulus using ultrasound shear wave elastography (SWE) in humans. We aimed to investigate thigh muscle stiffness in females and males, respectively, across a broad range of ages by using SWE. Eighty-six community-dwelling Japanese people who were aged 30 to 79 years and did not regularly exercise participated in this study. The vastus lateralis (VL) shear modulus was measured at three different knee joint angles: full extension, 90° of flexion, and full flexion. There were no significant main effects of sex or age on the VL shear modulus in full extension or 90° of flexion of the knee. However, the VL shear modulus in knee full flexion was significantly smaller in females than in males and increased with age from 47.9 years. The results suggest that the accelerated increase in VL stiffness that occurs after an individual passes their late 40s may be an important therapeutic target for developing effective treatments and programs that preserve and improve quality of life.
Highlights
Skeletal muscle fibrosis, an excessive accumulation of extracellular matrix (ECM) components, occurs with aging [1,2]
It is likely that muscle fibrosis, an excessive accumulation of ECM components, can be detected using ultrasound shear wave elastography (SWE) only when muscle stiffness is measured in positions in which the muscle is stretched
Serum hormone levels were not measured in this study, our findings suggest that the effect of the level of sex hormones decreasing due to menopause on muscle stiffness is negligibly small and that the cumulative effect of sex hormones over several decades prior to menopause in females is much larger
Summary
An excessive accumulation of extracellular matrix (ECM) components, occurs with aging [1,2]. Advanced muscle fibrosis with aging leads to impaired muscle regeneration [3]. Muscle fibrosis and the associated increase in muscle stiffness are suggested to impair mobility and exercise capacity, thereby decreasing the quality of life of elderly people [2]. Muscular conditions in relation to fibrosis need to be assessed quantitatively to develop effective treatments and programs that preserve and improve quality of life. There is growing evidence indicating that ECM components are primarily responsible for muscle stiffness [4,5]. Animal experiments have revealed that muscle bundles, which consist of several muscle fibers and contain ECM components, displayed more than 5-fold stiffness than individual muscle fibers and muscle fiber groups, excluding
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