Which measure is most indicative of somatic protein in skeletal muscle?

Mid-arm muscle circumference is the most indicative measure of somatic protein in skeletal muscle because it directly assesses the muscle mass in the upper arms. This measurement reflects the size of skeletal muscle and is often used to evaluate nutritional status and body composition in individuals, particularly in terms of their muscle reserves.

Unlike serum proteins such as albumin and transferrin, which can be influenced by several factors beyond muscle mass (such as hydration status or liver function), mid-arm muscle circumference directly correlates to the body's muscle stores. It is a practical and reliable anthropometric measurement that provides insight into muscular health and nutritional deficiencies, particularly in populations at risk for malnutrition or muscle wasting.

The other options, while relevant indicators of overall nutritional status or hydration, do not provide a direct measurement of somatic protein in skeletal muscle.