The mid-arm circumference of the upper arm muscle measures the distance around the biceps and other muscles of your arm halfway between your shoulder and elbow joint. This measurement is used to check for athletic fitness and weight gain. It is also used in anthropometric measures of skeletal muscle mass and to estimate the amount of muscle protein in your body. The National Kidney Foundation notes that almost 60 percent of the total body protein is found in your skeletal muscle. Hence, this muscle circumference can help determine your nutritional intake. You can calculate your mid-arm circumference on your own to determine athletic fitness.
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Stand in front of a mirror to determine the midpoint on your upper arm. Hold your arm away from your body, but do not contract the muscle, as flexing the bicep will make the circumference larger. You can hold one end of a measuring tape against the inside of the muscle midway down your upper arm.
Circle the tape around the arm to determine the circumference of the upper arm muscle. Have someone help you if you cannot manage this with one hand. The muscles in this area include the biceps brachii on the upper side of the humerus arm bone and the triceps brachii on the posterior or lower side.
Note the circumference measurement and write it down. You can repeat the measurement on the other arm, but it should be the same in most cases. If you are trying to build muscle mass, it is a good idea to measure the upper-arm circumference every 1 to 2 weeks to assess your progress.