By means of the ultrasonic photography of the cross-section of the acting muscle bundle, together with the measurement of the muscle strength developed by the subject with maximum effort, the strength per unit area of the muscle was calculated in 245 healthy human subjects, including 119 male and 126 female.
The result was summarized as the following:
| 1. |
The ultrasonic method used in this work was possibly admitted as the best way to calculate the cross-sectional area of the muscle.
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| 2. |
The arm strength was fairly proportional to the cross-sectional area of the flexor of the upper arm regardless of age and sex.
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| 3. |
The strength per unit cross-sectional area of flexor of the upper arm was 6.3 kg/cm2 in the average, standard deviation of 0.81 kg/cm2. When cross-sectional area of muscle was measured at extensive position of the forearm the strength per unit area was calculated to be 4.7 kg/cm2 at flexed position of the forearm.
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| 4. |
As to the individual variation, the strength per unit area was distributed in a range from 4 kg/cm2 to 8 kg/cm2.
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| 5. |
The strength per unit cross-sectional area was almost the same in male and female regardless of age. In addition to that, there was not found any significant difference in ordinary and trained adult.
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