The age-old question of quantity vs. quality can also be asked of muscle. Is the quantity of muscle mass (i.e., total muscle mass) more important than the strength of the individual muscle (i.e., muscle quantity)? Researchers as well as strength coaches and athletes have wrestled with this question for years.
The first step in answering this question is to define both muscle quantity and muscle quality to determine how to measure it. Of the two, muscle quantity is the easiest to define and the easiest to measure. In most individuals, skeletal muscle mass is the largest component in the human body. Total skeletal muscle mass can be accurately determined with a variety of techniques. Computed axial tomography (CT) and magnetic resonance imaging (MRI) offer the most accurate methods, however, both methods are costly and access to these devices is limited. An alternative to measuring skeletal muscle mass by these two methods is dual X-ray absorptiometry (DXA), which is extremely accurate and widely available. Although DXA does emit some radiation, the amount that the individual is exposed to is minimal. Although bioelectrical impedance (BIA), hydrostatic weighing, etc. claim to measure skeletal muscle mass; they actually measure fat-free mass which combines both muscle and bone and therefore it is not possible to accurately determine skeletal muscle mass.
Compared to muscle mass, muscle quality is a little more difficult to define and measure. In the simplest terms, muscle quality can be defined as the capacity of muscle to generate force. The generation of muscle force is the result of a series of complex interactions dependent on a number of factors such as angle of the muscle fibers, fat infiltration, fiber type, and the extracellular matrix (Narici et al., 2003; Goodpaster et al., 2001; Kjaer, 2004) as well as neural factors (Clark et al., 2011). From this definition, one can see determining the quality of the muscle is more complex than simply determining the skeletal muscle mass. As a first step, one would have to determine the strength of the muscle. Although there are a number of tests such as one repetition maximal that can determine one’s strength these measures often measure a group of muscles instead of a single muscle. The use of isokinetic dynamometer can be used to isolate muscles to some degree, however, the movements that these devices utilize often require a group of muscles. Even a device such as a handgrip dynamometer requires more than just a single muscle to perform the required movement. The other issue with determining muscle quality is measuring the muscle. Although DXA can measure total muscle mass as well as regional (i.e., arm, legs, etc.) with a high degree of accuracy it cannot measure an individual muscle. For the measurement of an individual muscle it would require the use of CT or MRI. As previously stated both of these methods are costly and often have limited availability. Ultrasound has been suggested as a possible way to measure the mass of an individual muscle (Kellis et al., 2021), however, there are questions about the accuracy of this method and it is time-consuming to make these measures. So is it possible to really measure muscle quality?
The answer is yes, but with some limitations. We have to remember that most of the time when we measure muscle strength we are measuring a muscle group. For instance, muscle extension using an isokinetic dynamometer requires the activation of rectus femoris, vastus lateralis, vastus medius, and vastus intermedius, while muscle flexion requires the activation of biceps femoris, semitendinosus, and semimembranosus. It is important to point out that doing these measurements does not take into account the role of antagonist muscles or neural component of force generation. In addition, as previously pointed out, if you are using DXA you can only measure the muscle mass in a region. Although it is possible to measure anterior and posterior aspects of the leg muscle as we have demonstrated (Raymond-Pope et al., 2017), even those measures cannot separate the individual muscles within these regions. It is possible to use ultrasound, MRI or CT to make measurements of individual muscles but these methods are typically time-consuming and/or costly. In addition, there are still limitations to making accurate measures of an entire muscle and not just a representative section.
So what is the take-home message? Which is more important, muscle quantity or muscle quality? I think both are important, but muscle quality is an emerging area of importance. Currently, the difficulty in measuring individual muscle size and or volume, as well as strength of a particular muscle, is a limitation. However, we can measure muscle mass for a given area or region and we can measure muscle strength for a given region as well. So given this limitation, we can measure muscle quality group or region of muscles. As new technologies and methods emerge, the ability to measure muscle quality for a particular muscle is coming closer to a reality.
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About the Author
Donald Dengel, Ph.D., is a Professor in the School of Kinesiology at the University of Minnesota and is a co-founder of Dexalytics. He serves as the Director of the Laboratory of Integrative Human Physiology, which provides clinical vascular, metabolic, exercise and body composition testing for researchers across the University of Minnesota.