Measuring the upper arm muscle circumferenceThe upper arm muscle circumference is, together with the triceps skinfold, a measure for the quantity of fat and muscle mass in the body. This method is based on the assumption that the measured muscle circumference is representative for the rest of the body.
Besides that, it is assumed that there is an equal distribution of fat around the arm and that there is a constant amount of bone compared to the muscle area. The upper arm fat mass (F), also measured by upperarm circumference and the triceps skinfold (T), provides a better assessment of the total body fat mass compared to a single skinfold measurement. The thickness of the triceps skinfold and the area of the upper arm decreases if the patient has malnutrition. Repeated measurements can give us an indication about changes in body composition and nutritional status of the patient.
A.R. Frisancho (1981) has published tables with percentiles, which can be used to compare the measured values with the values of a general population. Therefore, when a patient's percentiles are low, he/she belong to the group of skinny people. McWhirter (1994) demonstrated in his research that an upperarm muscle circumference below P15 indicates malnutrition, and a value below the 5th percentile points to severe malnutrition. These values are, however, not a very reliable measure. When a patient has a constant upper arm muscle circumference (f.e. p60) and it drops to P50, malnutrition is a possibility although the muscle circumference is not below P15. The change in time is a better measure for the nutritional status.
ReliabilityA disadvantage of this method is that the results are not reliable in patients with oedema in the upper extremities, or people who are immobile because of a muscle disease.
Measuring the upper arm circumference and triceps skinfoldMeasurements of the upper arm circumference and triceps skinfold are easy, cheap and not painful for the patient. The middle of the right upper arm is measured with a measuring tape (Frisancho):
- Determine the middle between the top of the shoulder and the point of the elbow, and mark this point;
- Now you measure the upper arm circumference. Place the measuring tape gently around the arm - do not pull;
- Measure the triceps skinfold at the back of the arm at the same height as the upper arm circumference, by using a skinfold caliper;
- Take the skinfold in a vertical position between thumb and pointing finger;
- Ask the patient to stretch his arm and strain his muscles, so that the muscles are not part of the skinfold;
- Ask the patient to relax his arm and let it hang down along the body;
- Place the caliper on the skinfold;
- Let go off the handgrip and wait two seconds before reading the value;
- Repeat this measurement three times;
- Calculate the mean of the three measurements.
Reference values for upper arm circumference, upperarm muscle circumference and triceps skinfold are also published by Jelliffe (1966) and are often used as a reference. However, these reference values are often criticised. The references published by Frisancho (1974/ 1981) were recommended, because these were taken by a more representative population. A comparison is made by Harries (1982) and showed that there is no similarity between the two, therefore it is important to mention which reference is used. According to Ravasco's article (2002) upperarm circumference is a useful tool to determine the nutritional status of ICU patients. The criteria from Mcwhirter (1994) and Blackburn (1977) were used. Muscle mass was measured on the non-dominant arm and was classified in three categories: normal, middle and severe depleted.The reference values can be found in the tables below, containing the percentiles (source: A.R. Frisancho, 1981).
- Triceps skinfold in mm.
- Upper arm circumference and the upper arm muscle circumference in mm².
- Upper arm area in cm².
- Upper arm muscle area in mm² and the upper arm fat area in mm².
- Upper arm muscle circumference (S) in mm: S = c - ( T * 3.14)
- Upper arm area (A) in mm² : A = c² / 12.56
- Upper arm muscle area (M) in mm² : M = S² / 12.56
- Upper arm fat area (F) in mm² : F = A - M