Sarcopenia refers to the loss of muscle mass, strength and endurance, and begins as early as our 30s. We lose about 8% of muscle mass per decade until we reach age 70, after which the loss increases to 15% per decade. By the time we’re in our 80s, we’re likely to have about 50% of our muscle that we had in our youth.[1]^{, [2]}Sarcopenia can lead to body composition changes, loss of mobility and independence, as well as increased risk of disability and earlier mortality. There are a variety of factors that impact the quantity and quality of muscle as we age, including environmental factors, and changes in the muscles, nervous system, immune system and hormones: [3]

Muscle matters

Skeletal muscle is attached to the skeleton and, through our control, help us to move our bodies. These muscles are generally comprised of two groups of fibres. Type 1 are considered slow oxidative or slow twitch fibres. Type 2 are called the fast glycolic or fast twitch fibers. Slow twitch fibres are the ones generally engaged during low intensity activity. Most strength generated comes from type I fibers, and these are ones used in maintaining posture. Fast twitch fibers produce rapid, forceful contractions to make quick, powerful movements. These fibers fatigue quickly, meaning they only be used for short periods. As we age, atrophy affects type II fibers almost exclusively.[4]

With age, we also experience decrease in satellite cells, which are stem cells that are activated in response to muscle injury or stress caused by heavy muscle use (weight-bearing activity) to begin the process of muscle repair and regeneration. Reduction of satellite cells is also most obvious in the type-2 skeletal muscle fibers. [5]

Finally, research shows that as we age, adipose tissue (fat) infiltrates muscle tissue. Loss of muscle mass triggers a 2–3% decline in basal metabolic rate (BMR) each decade after the age of 20 years and 4% per decade after the age of 50 years. A reduced BMR obviously influences fat-burning. These changes in body composition have been identified as sarcopenic obesity.[6]

Nervous system

Groups of motor units work together to contract a single muscle. Throughout the lifespan, skeletal muscle undergoes a continuous cycle of reinnervation (nerve supply) and denervation (loss of nerve supply), much like the process of bone-building and tear-down. As we age, however, denervation outpaces innervation, which contributes to the loss of motor units. Research shows that we maintain motor unit numbers into the our 60s, when they start to decline rapidly. [7]

Immune system

Immune cells are important for myogenesis (muscle tissue formation) and regeneration. Aging of immune white blood cells called macrophages has been implicated in the decrease in the number and ability of satellite cells to form muscular tissue. Aging also contributes to an imbalance in inflammatory and anti-inflammatory networks that causes a low-grade, chronic systemic inflammation termed inflammaging.[8]

Among other things, inflammaging is associated with muscle wasting. Increased visceral fat also triggers a higher secretion of pro-inflammatory adipokines associated with insulin resistance and muscle catabolism. In other words, there is a circular relationship between muscle loss and fat gain that may lead to more sarcopenia and then to further metabolic problems and inflammation.⁸

Hormones

Aging is associated with changes in hormones production and sensitivity that influence muscle anabolism and catabolism. There is a decrease in both growth hormone and androgens as we age, as well as increases in cortisol production in both sexes. These decreases parallel changes in body composition that include increased visceral fat as well as decreased lean body mass and bone strength. Significantly, studies so far do not show that GH and testosterone therapy is beneficial. It’s possible that increased visceral fat cells combined with the loss of fat burning potential due to declining growth hormone levels amplify the fat problem. ¹

Environment: Diet and exercise

Exercise to maintain and build muscle is critical for sarcopenia prevention and management in myriad ways. Let’s also pick up the thread about insulin resistance. Research shows that exercise improves metabolic control by increasing muscle glucose uptake during muscle contractions by mechanisms that do not depend on insulin. Muscle remains more sensitive to insulin for 24–48 h after exercise, even for those with type 2 diabetes. Although resistance training is critical for muscle building, aerobic exercise is also essential for anabolism as it may help to increase amino acid delivery to muscle.³

From the lab:

Research suggests that supplementation with essential amino acids – especially branch chain amino acids – may help to build and repair muscle tissue and increase skeletal energy uptake.[9] Some evidence suggests that protein supplementation is anabolic, and that whey protein may have an improved anabolic effect over more slowly absorbed proteins.[10] Collagen supplementation has also been shown to build lean muscle when combined with regular resistance training and a healthy balanced diet.[11]

Reviews of individual nutrients show that selenium and calcium are associated with muscle mass, while magnesium, selenium, iron and zinc are associated with physical performance in older adults.[12] Adding vitamin D to protein supplementation appears to promote muscle health improvements in research.¹⁰ Finally, research has shown that omega 3 supplements may help to promote anabolism and functional decline in older adults.[13]

Nutrients to support muscle health

Research has also shown we should aim to consume 25-30 g of protein at each meal and reach intake levels of 1.2 g/ kg body daily to maximize muscle protein.¹⁰ Long-terms prevention and care strategies should also include a focus on glucose⁶ and stress (cortisol)[14] management.

© 2020 Jamieson Wellness University

[1] Kim, T.N., &Choi, K.M. (2013) Sarcopenia: Definition, Epidemiology, and Pathophysiology. Bone Metab 2013;20:1-10 http://dx.doi.org/10.11005/jbm.2013.20.1.1

[2] Evans, W. (2010). Skeletal muscle loss: cachexia, sarcopenia, and inactivity, The American Journal of Clinical Nutrition, Volume 91, Issue 4, , Pages 1123S–1127S https://academic.oup.com/ajcn/article/91/4/1123S/4597225

[3] Cruz-Jentoft, A., & Landi, F. (2014). Sarcopenia. Clinical Medicine (London, England), 14(2), 183–186. https://doi.org/10.7861/clinmedicine.14-2-183

[4] BC Open Text. Anatomy and Physiology. Chapter 10: Muscle Tissue. Accessed Jan 22, 2020. https://opentextbc.ca/anatomyandphysiology/chapter/10-5-types-of-muscle-fibers/

[5] Almeida, C., Fernandes, S., Ribeiro Junior, A., Okamoto, O., & Vainzo, M. (2016). Muscle Satellite Cells: Exploring the Basic Biology to Rule Them. Stem Cells International. 1-14 https://doi.org/10.1155/2016/1078686

[6] Cleasby, M., Jamieson, P., & Atherton, P. (2016). Insulin resistance and sarcopenia: mechanistic links between common co-morbidities, Journal of Endocrinology, 229(2), R67-R81. Retrieved Jan 22, 2020, from https://joe.bioscientifica.com/view/journals/joe/229/2/R67.xml

[7] Narici, M., & Maffulli, N. (2010). Sarcopenia: characteristics, mechanisms and functional significance British Medical Bulletin; 95: 139–159 DOI:10.1093/bmb/ldq008

[8] Dupont, J., Dedeyne, L., Dalle, S., Koppo, K., & Gielen, E. (2019). The role of omega-3 in the prevention and treatment of sarcopenia. Aging Clinical and Experimental Research, 31(6), 825–836. https://doi.org/10.1007/s40520-019-01146-1

[9] Hidekatsu Y. (2015). Nutrition for Sarcopenia. J Clin Med Res. 2015;7(12):926-931

[10] Rondanelli, M., Faliva, M., Monteferrario, F., Peroni, G., Repaci, E., Allieri, F., & Perna, S. (2015). Novel insights on nutrient management of sarcopenia in elderly. BioMed Research International, 2015, 524948.

[11] Jendricke, P.; Centner, C.; Zdzieblik, D.; Gollhofer, A.; König, D. Specific Collagen Peptides in Combination with Resistance Training Improve Body Composition and Regional Muscle Strength in Premenopausal Women: A Randomized Controlled Trial. Nutrients 2019, 11, 892. https://doi.org/10.3390/nu11040892

[12] van Dronkelaar, C., van Velzen, A.,  Abdelrazek, M., van Der Steen, A., Weijs, P., & Tieland, M. (2018). Minerals and Sarcopenia; The role of Calcium, Iron, Magnesium, Phosphorus, Potassium, Selenium, Sodium, and Zinc on Muscle Mass, Muscle Strength, and Physical Performance in Older Adults: A Systematic Review. Journal of the American Medical Directors Association, Vol.19(1), pp.6-11.e3

[13] Di Girolamo, F; Situlin, R; Mazzucco, S; Valentini, R; Toigo, G; Biolo, G. (2014). Omega-3 fatty acids and protein metabolism: enhancement of anabolic interventions for sarcopenia.  Current Opinion in Clinical Nutrition and Metabolic Care: March 2014 - Volume 17 - Issue 2 - p 145–150  doi: 10.1097/MCO.0000000000000032

[14] Lang, T., Streeper, T., Cawthon, P., Baldwin, K., Taaffe, D.R., & Harris, T.B. (2010). Sarcopenia: etiology, clinical consequences, intervention, and assessment . Osteoporos Int (2010) 21:543–559 DOI 10.1007/s00198-009-1059-y