Summer 2022 Newsletter
By David Church, PhD, CSCS*D
Department of Geriatrics, College of Medicine
University of Arkansas for Medical Sciences
Skeletal muscle mass, function, and strength decline with increasing age, a condition that has been coined “sarcopenia”1. Sarcopenia increases the risk of deleterious health conditions and represents a major financial cost to healthcare systems. Among older adults who are hospitalized, those with sarcopenia on admission are 5-fold more likely to incur higher hospital costs than those who do not.2 The economic burden of sarcopenia on the US healthcare system is considerable, with one estimate of the total annual cost of hospitalization for sarcopenic individuals being USD $40.4 billion3. From a clinical practice perspective, individuals with sarcopenia are at a greater risk of falling, reduced mobility and independence, and 95% more likely to be hospitalized as compared to those without sarcopenia3.
The term sarcopenia, coined in 1989, refers to the loss of muscle mass1. Since then, greater insights into muscle strength, mass, and function have developed. It has been demonstrated that low muscle mass is associated with weakness, and that weakness is strongly associated with function and disability. However, low muscle mass alone is weakly or not associated with function and disability2–5. As a result, current sarcopenia definitions incorporate measures aimed at muscle mass, strength, and function. The majority of sarcopenia research focuses on prevention and treatment. Of this work, there is even less attention given to the standardization of assessment and diagnostic criteria. Multiple working groups of experts have weighed in, including those previously mentioned2,6,7; however, there are also the National Institute on Aging (NIA), the Foundation for the National Institutes of Health funded Sarcopenia Definitions and Outcomes Consortium (SDOC)4, and the Asian Working Group for Sarcopenia (AWGS)5. While important initiatives, the results have led to different definitions and clinical assessments for the same disease. Further, when looking into one working group, SDOC, the level of agreement amongst 13 different position statements varies widely4. Thus, uncertainty surrounding the definition and outcomes of sarcopenia is high even amongst international experts. Most striking is the fact that current diagnostic criteria and cutoffs only identify individuals with sarcopenia, NOT those “at risk” for sarcopenia. This is an important failing of the current diagnostic tests as these cut off points indicate the patient’s increased risk for falls, while independence, quality of life, and longevity are decreased2–4,8,9. Further, the regression and management of sarcopenia becomes a major economic burden to the healthcare system3. At this point, the best possible outcome is to slow the progression of the disease. In fact, the recent Sarcopenia Definitions and Outcomes Consortium (SDOC) states that since low grip strength and usual gait speed are independent predictors of falls, mobility limitations, hip fractures, and mortality in community-dwelling older adults, they should be included in the definition of sarcopenia4. Thus, current techniques and diagnostic criteria can only identify sarcopenia after a physical/functional impairment has occurred. As a result, clinicians must treat and manage the disease, as opposed to identifying susceptible individuals and taking preventative steps. Stated differently, clinicians are hoping to slow the rate of decline rather than maintain or improve muscle health.
Skeletal muscle amino acid metabolism dictates muscle health and functionality. Altered amino acid metabolism lead to decrements in muscle mass, quality, and performance8. Our laboratory, as well as others, have documented that the circulating essential amino acids (EAA) response to protein ingestion determines muscle amino acid metabolism10,11. This well-established phenomenon allows us characterize potential nutritional biomarkers following an EAA challenge in order to determine the state of muscle health. As no additional equipment will be required the proposed EAA challenge represents a potential low-cost solution to classifying patients’ skeletal muscle health. This initiative will leverage the well-established physiological role EAA play in muscle metabolism and health within the existing clinical infrastructure (i.e., basic phlebotomy procedures). The extrapolation of this work will be the development of a simple analytical tool that would provide clinicians the ability to discern alterations in muscle metabolism and health prior to a loss of function or overt development of sarcopenia.
1. Rosenberg IH. Sarcopenia: origins and clinical relevance. J Nutr. 1997 May;127(5 Suppl):990S-991S. PMID: 9164280
2. Cruz-Jentoft AJ, Bahat G, Bauer J, Boirie Y, Bruyère O, Cederholm T, Cooper C, Landi F, Rolland Y, Sayer AA, Schneider SM, Sieber CC, Topinkova E, Vandewoude M, Visser M, Zamboni M, Writing Group for the European Working Group on Sarcopenia in Older People 2 (EWGSOP2), and the Extended Group for EWGSOP2. Sarcopenia: revised European consensus on definition and diagnosis. Age Ageing. 2019 Jan 1;48(1):16–31. PMCID: PMC6322506
3. Goates S, Du K, Arensberg MB, Gaillard T, Guralnik J, Pereira SL. Economic Impact of Hospitalizations in US Adults with Sarcopenia. J Frailty Aging. 2019;8(2):93–99. PMID: 30997923
4. Bhasin S, Travison TG, Manini TM, Patel S, Pencina KM, Fielding RA, Magaziner JM, Newman AB, Kiel DP, Cooper C, Guralnik JM, Cauley JA, Arai H, Clark BC, Landi F, Schaap LA, Pereira SL, Rooks D, Woo J, Woodhouse LJ, Binder E, Brown T, Shardell M, Xue QL, DʼAgostino RB, Orwig D, Gorsicki G, Correa-De-Araujo R, Cawthon PM. Sarcopenia Definition: The Position Statements of the Sarcopenia Definition and Outcomes Consortium. J Am Geriatr Soc. 2020 Jul;68(7):1410–1418. PMID: 32150289
5. Chen LK, Woo J, Assantachai P, Auyeung TW, Chou MY, Iijima K, Jang HC, Kang L, Kim M, Kim S, Kojima T, Kuzuya M, Lee JSW, Lee SY, Lee WJ, Lee Y, Liang CK, Lim JY, Lim WS, Peng LN, Sugimoto K, Tanaka T, Won CW, Yamada M, Zhang T, Akishita M, Arai H. Asian Working Group for Sarcopenia: 2019 Consensus Update on Sarcopenia Diagnosis and Treatment. J Am Med Dir Assoc. 2020 Mar;21(3):300-307.e2. PMID: 32033882
6. Cruz-Jentoft AJ, Baeyens JP, Bauer JM, Boirie Y, Cederholm T, Landi F, Martin FC, Michel JP, Rolland Y, Schneider SM, Topinková E, Vandewoude M, Zamboni M, European Working Group on Sarcopenia in Older People. Sarcopenia: European consensus on definition and diagnosis: Report of the European Working Group on Sarcopenia in Older People. Age Ageing. 2010 Jul;39(4):412–423. PMCID: PMC2886201
7. Cederholm T, Barazzoni R, Austin P, Ballmer P, Biolo G, Bischoff SC, Compher C, Correia I, Higashiguchi T, Holst M, Jensen GL, Malone A, Muscaritoli M, Nyulasi I, Pirlich M, Rothenberg E, Schindler K, Schneider SM, de van der Schueren M a. E, Sieber C, Valentini L, Yu JC, Van Gossum A, Singer P. ESPEN guidelines on definitions and terminology of clinical nutrition. Clin Nutr. 2017 Feb;36(1):49–64. PMID: 27642056
8. Moore DR. Keeping Older Muscle “Young” through Dietary Protein and Physical Activity12. Adv Nutr. 2014 Sep 1;5(5):599S-607S. PMCID: PMC4188243
9. Mitchell WK, Williams J, Atherton P, Larvin M, Lund J, Narici M. Sarcopenia, dynapenia, and the impact of advancing age on human skeletal muscle size and strength; a quantitative review. Front Physiol. 2012;3:260. PMCID: PMC3429036
10. Church DD, Hirsch KR, Park S, Kim IY, Gwin JA, Pasiakos SM, Wolfe RR, Ferrando AA. Essential Amino Acids and Protein Synthesis: Insights into Maximizing the Muscle and Whole-Body Response to Feeding. Nutrients. 2020 Dec 2;12(12). PMCID: PMC7760188
11. Pennings B, Boirie Y, Senden JMG, Gijsen AP, Kuipers H, van Loon LJC. Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men. Am J Clin Nutr. 2011 May;93(5):997–1005. PMID: 21367943