Abstract
This study investigated age-related changes in muscle architectural characteristics and contributing factors influencing strength of elderly persons in the human quadriceps muscles. The subjects consisted of 31 elderly women aged 81.7 ± 6.4 years, and 21 young women aged 22.6 ± 2.5 years. Muscle thickness and muscle-fiber pennation angles were measured in the vastus lateralis using B-mode ultrasonography. The location used for imaging on the right vastus lateralis muscle was a point midway between the lateral condyle of the femur and the greater trochanter. Quadriceps strength was measured using isometric maximal voluntary contraction (MVC) of the knee extension. Cross-sectional area (CSA) was estimated from muscle thickness and thigh circumference measurements. Muscle-specific force was calculated from MVC to CSA ratios (MVC/CSA). The muscle thickness and MVC of quadriceps was a significantly greater in young women than in elderly women. Decrease with aging was relatively greater for muscle strength than for muscle size. In elderly subjects, there was a significant correlation between age and quadriceps strength, but not muscle thickness or CSA. Young women had significantly greater muscle-specific force than elderly women. Furthermore, coefficients of variation of muscle-specific force tended to be greater in the elderly than in the young. These findings suggest that the decrease in muscle strength with aging may also be influenced by neural activation ability as well as by muscle size, and that a large variability in this neural factor is found in the elderly.
