Research Flex  

Do you have good muscle health? That answer may vary depending on the clinician and their specialty.  

So far, no definitive definition exists for “muscle health,” but it’s worth exploring, says Michael Harris-Love, DSC, MPT, PT, FAPTA, professor of physical medicine and rehabilitation and associate dean of Physical Therapy Education at the University of Colorado Anschutz School of Medicine.  

Harris-Love, who also directs the CU Physical Therapy Program’s Residential DPT Pathway and is a health scientist at the Rocky Mountain Regional VA Medical Center, leads the 3MAP Lab, which focuses on muscle plasticity in response to training, detraining, normal aging, and chronic disease. Thinking about what constitutes muscle health is often front of mind.  

In a new literature review and proposed framework published in the Journal of Functional Morphology and Kinesiology, Harris-Love and his research colleagues explored some of the many definitions clinicians and researchers use and why standardization may be beneficial.  

Harris-Love says a muscle health definition could unite clinicians and researchers and be meaningful for patients, too.  

Why is a definition of muscle health important?  

In clinical practice, we often find that key questions about muscle health are raised only after an older adult experiences an injury or other disabling event. So, we hope that renewed discussion about this topic will amplify its importance among practitioners. It’s also important to work toward a common definition to ensure clinicians are speaking the same language and to aid the interpretation of research findings concerning muscle health.  

Muscle health seems to go well beyond just the muscles. How does that play into this work?  

The way a physician sees muscle depends on their specialty and the question they’re asking. When we talk about related concepts like muscle health and muscle quality, the imprecision of terms further removes us from a common definition or standardized assessments.  

In some of the papers that our lab has written, we've mentioned that identifying the domains of interest is important — such as metabolic function versus muscle force production — to improve scientific communication and help provide a framework for muscle heath assessment.  

You and your colleagues write that there's no standard definition, but there are some themes that emerge when clinicians and researchers talk about muscle health. Tell me about those.

We reviewed more than 300 papers and then got down to a smaller subset to ask this question of what muscle health is, and we were surprised by the large variety of different measures and assessment categories cited by investigators as components of muscle health.  

The three major components that we saw were body or tissue composition, some degree of muscle performance, and an assessment of functional performance.  

Functional tests alone can never tell you wholly about how muscle performs, but you need good functioning muscle to perform these types of tasks. So, we would never use the results of functional testing in isolation and make conclusions about muscle health. However, if I measure muscle strength directly, assess your functional status, and consider the properties of muscle tissue, such as your muscle composition and how much muscle mass you have, then I can start to make some clinical decisions. I begin to have enough information to understand if muscle impairments are a large part of why you can't complete a functional task.  

If everybody is thinking about muscle health a little bit differently, is it challenging to reach a consensus on a good definition?  

From a conceptual standpoint, I believe that we will come to an understanding or agreement about a common definition of muscle health. However, I think the definition of muscle health and how you assess muscle health are different questions.  

An example of that might be when you're diagnosing a rheumatological disorder. There is no single definitive test for rheumatoid arthritis and a patient’s results among a variety of diagnostic criteria serve to inform the clinical decision-making process. Moreover, access to more refined diagnostic tools such as advanced biomedical imaging varies based on the health care setting.  

In a similar fashion, the diagnostic tools available to rehabilitation specialists who rise to the challenge of assessing muscle health will vary widely. Some will have access to simple body composition tools such as bioelectrical impedance devices, while others will have the ability to estimate both muscle mass and muscle composition using advanced imaging techniques. In some clinics, grip strength testing will be readily available, but in other specialized settings, isokinetic dynamometers may be employed to provide detailed assessments of muscle performance.    

Given this clinical reality, I would suggest that our standards ultimately account for both low-cost assessment measures and more refined, confirmatory approaches. We need complementary, parallel pathways for researchers and clinicians to advance our understanding and improve practice.  

What would a standardized definition of muscle health mean for your work?  

Bringing investigators together around common concepts for assessing muscle health will serve to strengthen our research endeavors. When you look at pulling together a collection of studies over time, the use similar measures and common terms will allow us to conduct higher quality meta-analyses to help identify key gaps and guide our future investigative efforts.  

Reaching a common understanding about muscle health will also allow us to collectively move on to the critical issues: attaining consensus on standardized assessment protocols and addressing the details regarding test result weighting and interpretation. This is where the realwork will begin.  

Do you see a benefit for patients, too?  

Diminished muscle health is often hidden behind slow physical decline, the cessation of previous physical activities, and the gradual increase in caregiver burden. As the saying goes in the clinic, “You can’t manage what you don’t measure.” Skeletal muscle impairments can erode quality of life long before they lead to an injury or medical event.  

A proactive approach to assessment may lead to better patient outcomes and promote healthy aging.