This study aimed to investigate the influence of aging on muscle thickness in lower limbs, with specific emphasis on the site- and gender-related differences. Subjects were a total of 191 healthy young and elderly persons of both genders : 51 young men (24.2±3.6 yrs), 45 young women (23.1±3.2yrs), 51 elderly males, and 44 elderly females. Lower leg anterior, and lower leg posterior muscle thickness was determined using a brightness mode ultrasonographic apparatus. At all sites except for the thigh posterior, the muscle thickness values were significantly greater in the young than in the elderly groups of both genders, even in terms of the ratio of muscle thickness to body mass^1/3 (Mt/Wt^1/3 ratio), calculated to normalize the morphological differences. The relative difference in muscle thickness between the two age groups was the greatest at the thigh anterior and the least at the thigh posterior in both genders. Between young men and women, the men showed significantly greater muscle thickness and Mt/Wt^1/3 ratio at every site than the women. Between the elderly groups, however, Mt/Wt^1/3 ratios at all sites, except for the thigh anterior, did not show significant gender-related differences. Relative differences in both muscle thickness and Mt/Wt^1/3 ratio between the young men and women were similar among the sites, but between the elderly groups the corresponding values at the thigh anterior were greater than at the other sites. These results indicate that 1) the influence of aging on muscle thickness differs between the muscle groups located in the anterior and posterior sited within the same segment, 2) for women, the age-related loss of muscle thickness at the thigh anterior is relatively greater as compared to those at the other sites of the lower limb.

The influences of age on muscle architectural characteristics, i. e., muscle thickness, pennation angle, fascicle length, were studied in 121 men and 229 women aged 17 to 85 yrs. The subjects were divided into three age groups (younger : 17-39 yrs, middle-aged : 40-59 yrs, elderly : 60-85 yrs) for both genders. Muscle thickness and pennation angle of the vastus lateralis (VL), medial gastrocnemius (MG), and long head of triceps brachii (TB) muscles were measured using B-mode ultraso-nography, and fascicle length was estimated. In all age groups, men had significantly greater relative muscle thickness (to limb length) in VI, and TB than women, but not in MG. Relative muscle thickness of VL was significantly lower in elderly than in younger and middle-aged subjects. Ilowever, the corresponding differences in MG and TB were insignificant. The pennation angle of VL was significantly lower in elderly than in younger and middle-aged subjects, although there were no significant differences in pennation angles of MG and TB among the three groups. These results suggest that the decrease in thickness of vastus lateralis muscle with aging is significant, but not significant for medial gastrocnemius and triceps hrachii muscles.