Sex- and age-related differences in mid-thigh composition and muscle quality determined by computed tomography in middle-aged and elderly Japanese

Aim Sex‐ and age‐related differences in mid‐thigh composition and muscle quality remain unclear. The present study aimed to clarify these differences using computed tomography in middle‐aged and elderly J apanese. Methods A total of 2310 participants (age 40–89 years), who were randomly selected from the local residents, underwent computed tomography examination of the right mid‐thigh. Thigh circumference and cross‐sectional areas of the thigh, muscle, quadriceps, non‐quadriceps, fat, and bone were measured. Knee extension strength and muscle quality index (knee extension strength/quadriceps cross‐sectional area) were also assessed. Sex‐ and age‐related differences in these indices were analyzed. Results The thigh cross‐sectional area in men and women decreased by 0.6% and 0.5%/year, respectively, because of a decrease in muscle cross‐sectional area (men 75.2%, women 40.6%), fat cross‐sectional area (men 24.4%, women 59.6%) and bone cross‐sectional area (men 0.5%, women −0.2%). Muscle cross‐sectional area in men and women decreased by 0.6% and 0.4%/year, respectively, because of a decrease in quadriceps cross‐sectional area (men 65.6%, women 81.6%) and non‐quadriceps cross‐sectional area (men 34.4%, women 18.4%). Muscle quality in men and women decreased by 0.4% and 0.3%/year, respectively. Conclusion Thigh cross‐sectional area decreased with age mainly because of a decrease in muscle cross‐sectional area in men and fat cross‐sectional area in women. The rate of decrease in muscle cross‐sectional area was 1.5‐fold higher in men than in women. Muscle cross‐sectional area decreased with age mainly because of a decrease in quadriceps cross‐sectional area, especially in women. Decrease in muscle quality with age was similar in both sexes. Geriatr Gerontol Int 2015; 15: 700–706.