Developing Non-Invasive Measures of Muscle Quality in Older Adults

Many thanks to Dr. Eric Ryan for providing this week’s EXSS Impact content.  This work highlights recent efforts by Dr. Ryan and his research team to validate non-invasive measures of muscle quality to be used in older adults.  These findings demonstrate the potential for using ultrasound images to quantify muscle quality and have been recently published.

The Exercise and Sport Science Department at UNC-Chapel Hill. March 7, 2013 (photos © Kevin Seifert Photography | | (910) 250-9222)

Why did you do this study?

The older population (adults aged 65 years or older) is expected to double by 2050. It is recognized that age-related muscle weakness (i.e. dynapenia) is highly related to mortality, physical disability, and overall quality of life. Interestingly, the age-related loss of strength and skeletal muscle mass (i.e. sarcopeina) occur at different rates, suggesting muscle quality (e.g. amount of fat and/or connective tissue in a muscle) may be an additional physiological factor responsible for the reduction in strength and power observed in older adults.

Traditionally, muscle quality has been examined with magnetic resonance imaging or computed tomography scanning. However, the use of ultrasound (US) imaging to examine muscle quality has gained popularity because of its accessibility, portability and lack of ionizing radiation. The echo intensity (EI) or mean gray-scale value of an US image can provide a measure of muscle quality. A potential limitation of US scanning is that the reflection of an acoustic US wave is strongest when the propagation direction of that wave is perpendicular to the muscle fibers. In other words, changes in EI may reflect age-related changes in the angle of muscle fascicles (i.e. pennation angle) and not necessarily the quality of tissue. Therefore, the purpose of the present study was to determine if age-related differences in US derived muscle quality are influenced by the differences in pennation angle.

What did you do and what did you find in this study?

Using US, we measured muscle quality (EI) and the angle of muscle fascicles in the medial gastrocnemius in 24 young and 19 older men.   We found that the older men had poorer muscle quality and smaller pennation angles. However, the age-related differences in pennation angles had little to no influence on the US-derived measures of muscle quality.

Ultrasound image and muscle quality reading of an older individual

Older individual’s ultrasound image and muscle quality (echo intensity) reading

Ultrasound image and muscle quality reading from a younger individual's muscle

Younger individual’s ultrasound image and muscle quality (echo intensity) reading

How do these findings impact the public?

These findings suggest that EI, an US measure of muscle quality, does indeed reflect changes in muscle tissue composition commonly reported in older adults. Due to its portability, US is a promising method to examine muscle quality in variety of settings.