המקור
1. You Can't Flex Fat! Before skinfold caliper measurements, underwater weighings, and electrical impedance readings became popular to determine percentage of body fat, old timers had an interesting way to check their leanness. The test involved keeping a periodic record of the differences between the relaxed and contracted upper-arm measurements.
Before a workout and using a plastic tape, here's what they'd do:
1. Relax the arm and measure the circumference midway between the elbow and tip of the shoulder with the arm hanging away from the body. Record the number to the nearest 1/16th of an inch.
2. Flex the arm and measure it at right angles to the bone around the largest part of the contracted biceps with the upper arm parallel to the floor. Record the contracted arm to the nearest 1/16th of an inch.
3. Determine the difference between the relaxed and contracted measurements.
If you're trying to get leaner, or just out of curiosity, you should apply the same guidelines to your arm. Over several weeks, if you're getting leaner, the differences between your relaxed and contracted upper-arm measurements will get greater. If you're getting fatter, the differences between the two will get smaller.
The reason one goes up and the other goes down is the fact that...
you can't flex fat! Only muscle contains contractile tissue.
Most of your noncontractile fat is stored directly under your skin, with thicker layers around your hips and midsection. When your percentage of fat is reduced, it's reduced to a greater or lesser degree from all over your body.
Having 1-1/2 inches between the two measurements puts you at the approximate 10% level of body fat. A greater number is exceptional. The largest difference I've ever measured was on the arm of Casey Viator, who won the 1971 AAU Mr. America. Casey's right arm was 17-1/8 inches relaxed and 19-5/16 inches contracted — which amounted to 2-1/4 inches between the two numbers.
His body fat was 3%. When Viator raised his arms and contracted them, his biceps and triceps seemed to explode — which is no exaggeration.
By keeping accurate records of the differences between your relaxed and contracted arm measurements, you now have a simple way to monitor your leanness and fatness.