Extremely few studies have been published on the site of belly of thigh muscles. In our studies, 41 specimens (from 27 male and 14 female subjects) for anatomical investigation were used to examine the site of belly, which had often been employed for surface electromyogram. Not to say, “the belly of muscle” means the site showing the maximal value of circumference of each muscle.
The results were as follows.
1) Using nine thigh muscles, the full length of each muscle and the distance from the origin to the belly were directly measured at the first steps in the present study. Ratio of the distance from the origin to the full length was calculated. The ratio, as the average of all subjects, was 24.4% for M. sartorius, 30.8% for M. rectus femoris, 59.2% for M, vastus medialis, and 32.8% for M. vastus lateralis in the frontal aspect of thigh; 15.2% for M. gracilis, 67.9% for M. adductor longus in the inner aspect of thigh; and 44.1% for M. biceps femoris (caput longum), 29.3% for M. semitendinosus, and 65.5% for M, semimembranosus in the posterior aspect of thigh. However, no significant difference was found between the sex as well as age in the value of ratio.
2) Secondarily, “the cross section method” in this paper was used to evaluate the site of belly and measure the size of cross sections of M. sartorius and M, rectus femoris. The values were obtained from 3 specimens. The belly of M. sartorius was found at the site of 29% from the origin and that of M. rectus femoris was at 33%. The size of each cross sections was 1.3cm² and 3.5cm² respectively.
3) In addition, computed tomography was employed for 5 male adults to find the site of belly of M, sartorius and M. rectus femoris. The results were compared with those of specimens mentioned in 2) . The findings from the computed tomography showed the belly at the site of 25-29% from the origin for M, sartorius and 29-33% for M. rectus femoris. The size of cross sections of each muscle measured 2.9cm² and 11.4cm² respectively. These sites were confirmed to be coincided with those of anatomical specimens.
4) It can be, therefore, concluded that the values obtained from the direct method are applicable to those of living persons.