How to Calculate Mid-Upper Arm Muscle Circumference (MUAMC)

October 20, 2025 •

2 min read

According to the National Institutes of Health, mid-upper arm muscle circumference (MUAMC) can be a significant predictor of health outcomes related to muscle protein mass, particularly in the elderly. This guide provides a comprehensive and straightforward approach to understanding how to calculate mid-upper arm muscle circumference (MUAMC) accurately and effectively.

Quick Summary

A guide explaining the process for calculating mid-upper arm muscle circumference, a key indicator of lean muscle mass. Includes measurement steps, the formula used, and tips for accurate results and interpretation.

Key Points

Measurement is two-part: First, measure the Mid-Upper Arm Circumference (MUAC) and the Triceps Skinfold (TSF) separately.
Find the midpoint: Both measurements are taken at the midpoint of the non-dominant arm, between the shoulder bone and the elbow point.
Formula is key: The MUAMC is calculated using the formula: MUAMC = MUAC - (π × TSF).
Required tools: You will need a flexible measuring tape, a skinfold caliper, and a calculator.
Interpret changes over time: The greatest value of MUAMC is in monitoring trends, as a single measurement is less informative than observing changes over a period.

What is Mid-Upper Arm Muscle Circumference (MUAMC)?

Mid-Upper Arm Muscle Circumference (MUAMC) is an anthropometric measurement used to estimate muscle protein reserves by combining Mid-Upper Arm Circumference (MUAC) and Triceps Skinfold (TSF) thickness. This calculation helps differentiate the arm's muscle and fat components. It is a valuable, non-invasive tool for nutritional assessment, especially when other methods are difficult to use. A decline in MUAMC can indicate muscle wasting or malnutrition.

Why is MUAMC an important health metric?

MUAMC provides a more specific measure of muscle mass compared to general weight or BMI, isolating the muscle component. This makes it useful for detecting age-related muscle loss (sarcopenia) and screening for severe acute malnutrition (SAM). MUAMC assists healthcare professionals in tracking nutritional interventions.

Tools Required for MUAMC Calculation

To calculate MUAMC, you will need:

Flexible measuring tape: For MUAC.
Skinfold caliper: For TSF.
Calculator: To apply the formula.
Pen and paper: For recording measurements.

Step-by-Step Guide to Calculating MUAMC

Calculating MUAMC involves measuring MUAC and TSF, then applying a formula.

Step 1: Measure Mid-Upper Arm Circumference (MUAC)

Have the person bend their non-dominant arm at a 90-degree angle.
Locate and mark the midpoint between the shoulder (acromion) and elbow (olecranon).
With the arm relaxed, wrap the measuring tape around the midpoint, ensuring it's snug but not tight.
Record the measurement in centimeters.

Step 2: Measure Triceps Skinfold (TSF)

At the same midpoint mark, pinch a fold of skin on the back of the upper arm.
Place the caliper jaws on the skinfold below your fingers.
Read the value after a few seconds. Take three measurements and average them for accuracy.
Record the average measurement.

Step 3: Apply the MUAMC Formula

Calculate MUAMC using this formula:

MUAMC (mm) = MUAC (mm) - (3.1415 × TSF (mm))

Ensure both MUAC and TSF are in the same unit (e.g., millimeters) before calculation.

Interpreting Your MUAMC Results

MUAMC results are interpreted by comparing them to reference values for age, sex, and population. Tracking changes over time is more informative than a single measurement. Clinical thresholds are often used to classify nutritional status.

Comparison Table: MUAMC vs. MUAC


Feature	Mid-Upper Arm Muscle Circumference (MUAMC)	Mid-Upper Arm Circumference (MUAC)
Measurement Type	Indirect (calculated)	Direct
What it Assesses	Estimates lean muscle mass	Measures total arm size (muscle + fat)
Utility	More specific for muscle protein; detects sarcopenia	Screens overall nutritional status, malnutrition
Equipment	Tape and caliper	Tape only
Accuracy	Better reflects muscle mass changes	Less specific, includes fat
Common Use Case	Detailed clinical assessment	Rapid screening

Conclusion

Calculating mid-upper arm muscle circumference provides an effective estimate of muscle protein reserves through simple measurements and a formula. By determining MUAC and TSF and applying the standard calculation, you gain a valuable metric for nutritional assessment. Monitoring MUAMC over time is key for understanding health trends like muscle loss. MUAMC is a powerful, non-invasive tool for health monitoring and assessment.

Frequently Asked Questions

MUAC (Mid-Upper Arm Circumference) is a total measurement of the arm's girth, including both fat and muscle. MUAMC (Mid-Upper Arm Muscle Circumference) is a calculation that subtracts the fat component (estimated via triceps skinfold) to specifically estimate muscle mass.

You should measure the non-dominant arm. For example, if you are right-handed, use the left arm.

A non-stretchable, flexible tape measure is crucial for accuracy. Using one that can stretch may lead to inconsistent and unreliable measurements.

The frequency depends on the purpose. In a clinical setting, a dietitian can advise on the schedule. For personal tracking, consistency is key, and measurements should be taken at regular intervals under similar conditions.

While MUAMC can provide a general indication of a likely BMI range, especially when a person's weight cannot be measured, it is not a direct substitute. It serves as an estimate, particularly useful for screening.

Yes, MUAMC reference values and percentiles vary by age, sex, and population. It is important to compare your results with the appropriate reference data for accurate interpretation, especially in elderly or pediatric populations.

A result below the standard reference values may indicate low muscle mass or muscle wasting, which can be a sign of malnutrition or sarcopenia. It warrants further evaluation by a healthcare professional.