Abstract
Site-specific thigh muscle loss may be independent of age-related whole body muscle mass loss detected by using dual- energy X-ray absorpotiometry (DXA). Site-specific thigh muscle loss can be assessed by two major methods, i.e., magnetic resonance imaging (MRI) or computed tomography (CT) and ultrasound. Objectives: The purpose of this review is to discuss whether the magnitude of age-related declines in anterior and posterior thigh muscle size differs among previous studies with different methods for assessing muscle size. Age-related changes in absolute and relative knee extension (KE) and flexion (KF) strength and possible reasons for the age-related site-spe- cific thigh muscle loss are discussed. Design and Method: Non-systematic review. Results: The results of MRI/CT and ultrasound studies both suggest that age-related thigh muscle loss differs between the anterior compartment (i.e., quadriceps) and posterior compartment (i.e., hamstring) with much larger losses occurring in the anterior thigh compared with the posterior thigh. Previous studies investigating the age-related changes in absolute KE and KF strength are not as consistent. However, age-related change in muscle quality (strength per unit of muscle size) may not differ between KE and KF in an individual, although the values may differ among individuals. A major reason for the site-specific thigh muscle loss with advancing age may be the intensity and duration of daily physical activity which may secondarily influence other factors such as motoneuron loss and muscle protein metabolism. Conclusions: A ratio of anterior to posterior MT determined by ultrasound may correspond well to a multidimensional vari- able (CSA or MV) of the quadriceps to other thigh muscles (including both hamstring and adductor muscles) ratio, but not to the quadriceps to hamstring ratio. If there are similar changes in muscle quality with advancing age between knee extensor and flexor muscles, the anterior to posterior MT ratio may be involved in a ratio of muscle force of knee exten- sor and flexor muscles.
