Saturday, September 18, 2010


Background: In recent years there has been a growing effort to develop definitions and algorithms for defining both the age-related loss of muscle strength as well as the age-related loss of muscle mass. The term sarcopenia has become synonymous with the age-related loss of muscle mass— and at times has also been defined as the age-related loss of muscle strength. We have recently argued that the age-related loss of muscle strength is only partially explained by the reduction in muscle mass, and that other physiologic factors explain muscle weakness in older adults. Accordingly, we recently proposed that these two events (strength loss and mass loss) need to be defined independently. We have previously coined the term ‘dynapenia’ to describe the age-related loss of muscle strength.

The editors of the Journals of Gerontology: Biological and Medical Sciences recently invited us to write an update on our aforementioned article on dynapenia. In our upcoming manuscript we will propose a working decision algorithm to define dynapenia.



Working decision algorithm: Our central theme to this algorithm is that risk factors and screening exams are evaluated within the context of muscle weakness similar to that found in cardiovascular disease and diabetes. We felt a screening grip strength test and assessment of risk factors could be used in a complementary fashion. An individual with few risk factors and normal grip strength would “pass” screening and not be considered to have or be at elevated risk for dynapenia. Individuals with few risk factors but low grip strength— or high risk factors alone— would be referred for an advanced test assessing knee extensor maximal strength. We recognize that clinically relevant cut points of grip and knee extensor strength have yet to be fully characterized and developed. However, it is anticipated that these issues will be resolved with future studies. We should also note, that the algorithm illustrates the potential for additional testing on the etiology of dynapenia.

For more information on our prior work please see: 
http://www.ncbi.nlm.nih.gov/pubmed/18772470
http://www.ncbi.nlm.nih.gov/pubmed/20154609

Solicitation for Input: There is insufficient evidence in the literature to identify specific cut points, fully evaluate risk factors, and developed a final algorithm. However, we do wish to propose an early stage algorithm to encourage discussion along this line, and we would like to solicit your input on this algorithm (algorithm is shown above). Specifically, we would be grateful if you would vote on topic listed on the right side of the blog and provide comments as you see fit.

We thank you for your time and input on this matter.

Sincerely,

Todd Manini, Ph.D.                   Brian Clark, Ph.D.
University of Florida                 Ohio University
tmanini@aging.ufl.edu            clarkb2@ohio.edu

Disclaimer: The comments and results associated with this blog are available to the public and may be used in future presentations and publications.

10 comments:

  1. Dear Drs. Manini and Clark,

    This is certainly an interesting idea, and I look forward to your upcoming article. Thank you for stimulating discussion along this line.

    ReplyDelete
  2. Grip strength is:
    A. Easily measured and reproducible
    B. Correlated with strength measures in other parts of the body

    Knee strength is not so easily measured in the clinical setting.

    Will health professionals be able to bill for the service of assessing muscle strength?

    ReplyDelete
  3. Dear Drs. Manini and Clark,

    Thank you for the invitation to comment on your decision algorithm.
    As you know the European community has already proposed a similar algorithm (Cruz-Jentoft, Age Ageing (2010) 39 (4): 412-423.) Their approach starts by an age cut off (65 years) and then gait speed as the next test in the decision tree. They also use grip strength as a further test as well as measurement of muscle mass.
    I want to congratulate you for starting your algorithm by stratifying individuals based on risk factors (which in my opinion need to include history of falls and fear of falling as well as an assessment of physical function in a questionnaire).
    I noticed, however, that you have not included any tests of muscle power. Data from large aging studies (InChianti, Health ABC) have suggested that muscle power (gait speed, chair rise) are as good or may better in predicting outcomes (disability, QOL, mortality) when compared to muscle strength. These tests are also easily done in the office. They also have the advantage that no specialized equipment (apart from a stop watch) is needed. They also mimic natural movements and might not be as prone to learning effects and causing discomfort to the individual as grip strength and knee extensor strength.
    Have you considered integrating tests of muscle power in your algorithm?
    Although muscle mass might not be as strongly correlated to outcomes when muscle function (strength or power) is also used in the models, muscle mass might still be an important factor to assess especially if it can be done safely and reliably (for example by DXA). Further testing could also include the measurement of fat infiltration of muscle, which has been shown to correlate independently with outcomes (Health ABC). Although this is not a screening test it might be useful as a tool to determine the etiology of sarcopenia/dynapenia.
    Another way of defining sarcopenia/dynapenia could also be through criteria (like the new ACR rheumatoid arthritis criteria) in which a score is given for particular symptoms, physical findings, laboratory and imaging results. Sarcopenia/dynapenia would be present if a certain score is reached. Yet another way would be by defining a 10-year risk (similar to the FRAX calculator or Framingham calculator) and decide on an intervention threshold.
    I am glad to see that you have started the hard task of finding a definition of sarcopenia/dynapenia aiming to give clinicians the possibility to actually diagnose their patients with decreased muscle function.
    I hope these comments help you in this process.
    Sincerely, Bjoern Buehring

    ReplyDelete
  4. Dear Drs. Manini and Clark,

    Thank you for the invitation to comment on your decision algorithm.
    As you know the European community has already proposed a similar algorithm (Cruz-Jentoft, Age Ageing (2010) 39 (4): 412-423.) Their approach starts by an age cut off (65 years) and then gait speed as the next test in the decision tree. They also use grip strength as a further test as well as measurement of muscle mass.
    I want to congratulate you for starting your algorithm by stratifying individuals based on risk factors (which in my opinion need to include history of falls and fear of falling as well as an assessment of physical function in a questionnaire).
    I noticed, however, that you have not included any tests of muscle power. Data from large aging studies (InChianti, Health ABC) have suggested that muscle power (gait speed, chair rise) are as good or may better in predicting outcomes (disability, QOL, mortality) when compared to muscle strength. These tests are also easily done in the office. They also have the advantage that no specialized equipment (apart from a stop watch) is needed. They also mimic natural movements and might not be as prone to learning effects and causing discomfort to the individual as grip strength and knee extensor strength.
    Have you considered integrating tests of muscle power in your algorithm?
    Although muscle mass might not be as strongly correlated to outcomes when muscle function (strength or power) is also used in the models, muscle mass might still be an important factor to assess especially if it can be done safely and reliably (for example by DXA). Further testing could also include the measurement of fat infiltration of muscle, which has been shown to correlate independently with outcomes (Health ABC). Although this is not a screening test it might be useful as a tool to determine the etiology of sarcopenia/dynapenia.
    Another way of defining sarcopenia/dynapenia could also be through criteria (like the new ACR rheumatoid arthritis criteria) in which a score is given for particular symptoms, physical findings, laboratory and imaging results. Sarcopenia/dynapenia would be present if a certain score is reached. Yet another way would be by defining a 10-year risk (similar to the FRAX calculator or Framingham calculator) and decide on an intervention threshold.
    I am glad to see that you have started the hard task of finding a definition of sarcopenia/dynapenia aiming to give clinicians the possibility to actually diagnose their patients with decreased muscle function.
    I hope these comments help you in this process.
    Sincerely, Bjoern Buehring

    ReplyDelete
  5. Dear Drs Manini and Clark,

    This is a very interesting concept. I agree with Dr Bjoern Buehring that muscle power is more predictive of function, so a simple test of muscle power, such as the chair sit-to-stand or stair climb may be useful as well. I also like the idea of using other risk factors rather than only an age cut-off as there may be some adults over the age of 65 who are still incredibly strong.

    ReplyDelete
  6. With respect to the billing issue and screening, we use a quadriple screen in patients with primary myopathy - BIODEX: knee extension, arm curl, and dorsiflexion and then JAMAR handgrip - the knee extension and handgrip have CVs of < 2 % over a one year period and the testing takes about 15 minutes in the clinic and is extremely helpful to follow interventions (exercise, corticosteroids, IgG, etc.) - We are able to bill in Canada for this in patients with neuromuscular disease as a limited exercise testing code. I could envision such a screen for the older adult population and the tests cover the major muscle groups shown to correlate with functional outcomes and other health metrics in older adults.

    This could also be done using a cybex or other dynamometer and one could also easily add in a power component by using the integrated force over a given time period in the isokinetic mode.

    Sincerely,

    Mark Tarnopolsky, MD, PhD, Neuromuscular and Neurometabolic Disease Clinic, McMaster University, Hamilton, CANADA.

    ReplyDelete
  7. Drs Manni and Clark,

    I applaud you in considering that a loss of strength is different (and precursor) to sarcopenia. The earlier we can intervene, the better for the individual. I agree that power needs to be included in the assessment. A 5 repetition chair stand such as Women's Health and aging study uses is a relatively sensitive measure. Age should not necessarily be a cut off. In the clinic, chair stands combined with gait speed tells me the most about strength deficits related to function, especially when considering the difference between usual and fast gait speed.

    I look forward to further posts.

    Dale Avers PT DPT PhD

    ReplyDelete
  8. Alfonso Cruz-JentoftNovember 3, 2010 at 11:39 AM

    Dear Drs. Manini and Clark,

    I am presently unsure about the need to define dynapenia as a separate entity from sarcopenia. Muscle mass and muscle function are, of course, related, although many factors influence the interaction between both. But the same is true for other organs, like the brain or the kidney (is there a need to define low renal mass and low renal function?).

    Defining loss of mass as sarcopenia and loss of function (strength, power, performance) as dynapenia, as if the were separate entities may, in my modest view, lead to confusion. Our European group has proposed to link both aspects in the term "sarcopenia", as it has been successful in the literature already. I do admit that sarcopenia is not a brilliant word to define the problem, but... are dementia (“no mind”) or diabetes (“to go through”, referring to water through the body in poliuria) better terms to define complex diseases? I am concerned that changing the term at this time may bring confusion to many relevant partners, drug authorities and research funders included. Of course, I can agree with the concept under the word dynapenia, which is very valid and surely more relevant than muscle mass to clinical outcomes.

    Your suggestion to use risk factors instead of age cut-off points as a screening trigger is a very sound one (we have explored it recently, ie Curr Opin Clin Nutr Metab Care. 2010 Jan;13:1-7.). The main problem here is the lack of data to define a limited series of relevant risk factors of sufficient predictive value. This is probably the future of sarcopenia (dynapenia) screening and a nice area for research.

    A final question: is this algorithm proposed for research or for clinical practice? Do you believe that both aspects (looking for well defined homogeneous subjects for research and screening in geriatric/primary care clinics for direct medical care) can be covered with the same algorithm? Measuring grip strength may be easy to implement, but other measures of muscle strength (and power) are more time consuming and may need complex equipment not usually available in clinics.

    Thank you for opening this debate. I hope these comments are helpful and look forward to read your new green (or yellow?) banana.

    ReplyDelete
  9. Isabelle J. Dionne, PhDNovember 9, 2010 at 8:09 AM

    I think it's a great thing to open this discussion. I agree with you that muscle strength is totally independent than muscle mass and that strength has several asssociations with health parameters (chronic diseases, physical capacity and so on) whereas muscle mass does not (contrary to the general belief).

    In my opinion, muscle strength in itself is useful but when opposed to some adiposity index (such as body weight, BMI, or fat mass), it becomes even more pertinent. I would direct you to one of our papers (Choquette et al, JNHA, 2010) on this issue.

    If I can be of any help, feel free to ask.

    Regards,

    Isabelle J. Dionne, PhD
    University of Sherbrooke

    ReplyDelete
  10. Maurits Vandewoude, MD PhDNovember 10, 2010 at 7:46 AM

    Dear Drs. Manini and Clark,


    Thank you for opening the discussion on this topic. As Alfonso Cruz has pointed out, in the European working group there was some reluctance to introduce dynapenia as a separate concept next to sarcopenia. Of course, the loss of strength and function are pathophysiologically essential elements in the progress of frailty and in the development of disability.
    As age is a paramount important risk factor you might, in your screening approach, go for risk factor profile and/or age as a starting point.
    In the progress of functional disturbance there is a hierarchic relation between muscle strength and power/function. I wonder whether a measure for performance such as gait speed or chair rise would not be more interesting as the first measurement of the screening.
    I have also my reservations of knee extension as a measurement early in screening, since availability is limited in several clinical settings.

    ReplyDelete