Arm circumference is a widely used anthropometric measure, as it provides a quick estimate of a person's muscle mass. It is therefore used in the sports field, to monitor the degree of hypertrophy of the athlete, but also in the health sector, to evaluate the loss or purchase of lean mass (malnutrition, rehabilitation after trauma or surgery, convalescence, etc.).
Arm circumference as an indication of malnutrition
Average arm circumference in healthy adults:
MALES: 32 ± 5 cm FEMALES: 28 ± 6 cm
Arm circumference as an index of muscle mass
A simple indicator and particularly useful for estimating lean mass is the measurement of the muscle circumference of the arm. To obtain it, it is necessary to detect the skin fold at the level of the triceps (TS) and the circumference of the ipsilateral arm (AC).
The two data will be placed in the following equation:
Arm muscle circumference (AMC) = Cb - πP
where: Cb = circumference of the arm P = thickness of the triceps π = 3.14
Similarly, the muscle area of the arm (AMA) can be calculated:
Arm muscle area (AMA) = (Cb - πP) 2 / 4π
the total area of the arm (TAA)
Total area of the arm (TAA) = (Cb) 2 / 4π
and the "adipose area of the arm (AFA)
Arm adipose area (AFA) = TAA - AMA
N.B: the triceps fold is measured on the posterior side of the limb, halfway between the extremity of the acromion and the olecranon.
These formulas are based on the assumption that the section of the arm is approximately circular, that the subcutaneous adipose layer is uniformly distributed around the muscle and that the contribution of the bone is constant in the various subjects. This is obviously a theoretical model, which is not reflected in reality; however, given the simplicity and diffusion of this technique, its limits are accepted.
How is it measured?
The subject, with the upper limbs free from clothes, is in an upright position, the arms hang freely on the sides of the trunk and the palms of the hands are facing the thighs.
The circumference of the arm must be measured exactly halfway between the acromion and the olecranon, with the elbow flexed 90 °, in the non-dominant arm. Consequently, it is necessary to locate the midpoint of the arm with the elbow flexed at 90 ° and with the palm of the hand pointing upwards; once identified (with the help of the measuring tape), this point must be marked with a horizontal line of felt-tip pen.
The subject is invited to reposition the arm to the side of the trunk and proceed with the measurement (without compressing the soft tissues and keeping the meter perpendicular to the longitudinal axis of the limb, whose muscles must be relaxed).
Contracted biceps measurement (flexed arm circumference) is mainly carried out by bodybuilders to monitor the degree of muscle hypertrophy; those who practice this sport at the highest level reach circumferences close to 55-60 cm.
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