Leg ultrasound for fat content shown useful in assessing overall physical health

Using ultrasound to estimate the percent of intramuscular fat in lower extremities, researchers have shown an inverse association with physical activity levels and a positive association with body mass index, according to a small study published in the journal Muscle & Nerve.

Hui-Ju Young, PhD, University of Alabama at Birmingham, and colleagues looked at ultrasound results from 42 participants (16 men, 26 women) between 19 and 68 years old.

The subjects represented a wide range of body mass index and physical activity levels.

The researchers examined their intramuscular fat in four muscles—the rectus femoris (RF, part of the quadriceps); the biceps femoris (BF, the back of the thigh); the tibialis anterior (TA, mostly the shin); and the medial gastrocnemius (MG, the inside part of the calf).

Comparing the ultrasound results with other health measures, and quantifying muscle echo intensity using previously published equations, they found:

• strong correlations in percent intramuscular fat in all four muscles;  
• weak to moderate correlations between intramuscular fat and body mass index, waist/hip ratio, muscle thickness and muscle strength; and
• a relationship between intramuscular fat in RF and MG and physical activity.

As the study supports an association between the amount of intramuscular fat and other health conditions, “people with disabilities who have those conditions need a test that allows them to better understand their muscle composition,” Young explains in prepared remarks released by Wiley, publisher of Muscle & Nerve.

“Ultrasound may be especially useful for examining muscle fat in certain individuals,” he says. “For example, other imaging techniques such as DXA, MRI and CT do not work well on people who have metal implants, have muscle spasticity, are morbidly obese, or are pregnant.”