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. For instance, if you're an endocrinologist, you may be more concerned with the homeostasis of glucose than you are about muscle force production.
Also, 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.
In your latest paper, you write that there’s no standard definition, but there are some themes that emerge when clinicians and researchers talk about muscle health. What were you seeing?
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, so a biological measure, then some degree of muscle performance, and the third component was 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 the 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 what a good definition is?
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?
Physical health is freedom from ailments that result in physical impairments, along with having the ability to perform daily activities, functional tasks, and other physical activities without restriction. Ultimately, muscle health is the degree that the skeletal muscle system contributes to the status of our physical health.
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 real work will begin.
Do you see a benefit for patients, too?
We want clinicians to feel prepared to start timely conversations with their patients about muscle health. Estimates of body composition, strength, and functional status should be obtained for people at risk for muscle dysfunction due to chronic disease or geriatric syndromes. Patient care can benefit from even simple steps, such as charting serial measures of grip strength and customary walking speed.
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.
