Mid-upper arm circumference

The anthropometry of the upper arm is a set of measurements of the shape of the upper arms.

The principal anthropometry measures are the upper arm length, the triceps skin fold (TSF), and the (mid-)upper arm circumference ((M)UAC). The derived measures include the (mid-)upper arm muscle area ((M)UAMA), the (mid-)upper arm fat area ((M)UAFA), and the arm fat index. Although they are not directly convertible into measures of overall body fat weight and density, and research has questioned the connection between skinfold fat and deep body fat measurements, these measures are and have been used as rough indicators of body fat.

Factors influencing the bone, fat, and muscle composition of the upper arm include age, sex, nutritional status, fitness training level, and race.

The anthropometric measures of the upper arm are divided into principal measures, which are measured directly, and derived measures, which are derived from the principal measures using specific formulae and empirically-derived corrections. The derived measures attempt to provide better indicators of body composition and nutritional status than the principal measures, by accounting for the fact that external measurements of the arm necessarily compound measurements of bone, fat, and muscle.

The three principal anthropometric measures of the upper arm are the upper arm length, the triceps skin fold (TSF), and the mid-upper arm circumference (MUAC).

The triceps skin fold is the width of a fold of skin taken over the triceps muscle. It is measured using skinfold calipers. (See body fat percentage#Skinfold methods for general information on skinfold fat measurements.) The measurement is taken at a standardized position (one of eight standard skinfold measurement points) at the midpoint of the back of the upper arm. The skinfold calipers are spring-loaded. Holtain skinfold calipers are marked with 0.2 mm gradation, Lange calipers with 0.5 mm gradation.

The measurement is taken with the person standing upright, with arms hanging down loosely. The skin fold is pulled away from the muscle and measured with the calipers, taking a reading 4 seconds after the calipers have been released. The measuring point is half way between the olecranon process of the ulna and the acromion process of the scapula.

...
Wikipedia