|What is sarcopenia, and can we turn back the clock?
Harris, E.J. & Len Kravitz, Ph.D.
Sarcopenia (which means poverty of flesh) is the loss of muscle mass, strength, power and function as a result of aging (Sayer et al. 2013; Morely 2012). Morely continues that 5-13% of persons aged 60-70 years and 11-50% of persons in their 80s have sarcopenia. According to the United Nations Report (2002), the number of persons over 60 will increase from approximately 600 million in 2000 to about two billion in 2050. The report continues that the fastest growing group of the older population (in the world) is those who are 80 years of older. In 2000, this group numbered 70 million worldwide and projections are that it will increase five times that in the next 50 years. A major theme presented by the United Nations assembly on ageing is the provision of health care and support for older persons, including preventive and rehabilitative health care. As exercise professionals, it is imperative to realize that this exponential growing older population is likely to influence our clientele population, thus requiring a much more in-depth understanding of sarcopenia and the best interventions to manage it.
What are the Causes of Sarcopenia?
Although the causes of sarcopenia are multi-factorial, three major factors which will be discussed in this article are 1) a reduction in muscle innervation (activation), 2) oxidative damage by reactive oxygen species, and 3) nutritional factors associated with age (Doria et al., 2012; Sayer et al., 2013).
Reduced Muscle Innervation
Use it or lose it has long been a principle applied in the field of health and exercise and explains in part the first of the causes of sarcopenia-a reduction in muscle innervation. Morely (2012) states that the most dominant cause of sarcopenia is inactivity. Morely adds that inactivity is a widespread problem among all populations, not just the elderly. Muscle motor units (which consist of the motor nerve and the muscles fibers it innervates) are co-dependent, implying that when the motor neurons begin to die as a result of age and/or inactivity, denervation (interruption of the nerve connection) of the muscle fibers occurs-causing atrophy (wasting away) of the muscle cells. With the inactivity that often accompanies increasing age, there is a loss of motor neurons and a diminished function of the remaining motoneurons (Sayer et al., 2013). Importantly, the muscle contractions from exercise initiate the release of muscle growth factors, including insulin growth factor and mechanogrowth factor (Morely). These growth factors activate specialized cells in muscle (referred to as satellite cells), which promote protein synthesis. Aerobic exercise and resistance exercise play a major role in the prevention of muscle innervation problems, which lead to sarcopenia. Presently, no accepted exercise guidelines have been adopted for the prevention of sarcopenia, so professionals should refer to the most recent Physical Activity Guidelines for Adults and Older Adults: http://www.cdc.gov/physicalactivity/everyone/guidelines/adults.html
Reactive Oxygen Species
Reactive oxygen species (ROS) are chemically active molecules that contain oxygen. They are produced naturally by all tissues of the body as a result of aerobic metabolism, and serve to help with the cells' homeostasis (balance) regulation and cell messaging. However, due to their reactive nature, an over production of ROS may lead them to start attacking other molecules in cells, especially in muscle. Thus, these ROS are thought to play a key role in the development of sarcopenia (Sayer et al., 2013). Skeletal muscle, as the largest consumer of oxygen in the body, is quite vulnerable to high numbers of ROS build-up. These ROS can cause oxidative damage to mitochondrial (ATP power plant of cell) proteins, cell membranes and even DNA. Thus this damage causes impaired function of ATP (adenosine triphosphate, the energy currency of the cell) and in turn keeps the cells from carrying out many necessary metabolic functions. Apoptosis (the self-destruction of a cell) can also be caused by an accumulation of ROS within the mitochondria (Doria et al., 2012). The great news is that moderate and high intensity exercise promotes the production of powerful antioxidant (molecules that counteract oxidative damage) enzymes that combat the accumulation of ROS (Gomez-Cabrera et al., 2008).
Sayer et al. (20130 suggest that the literature indicates that diet also has an important modifiable influence on sarcopenia, with the most consistent evidence pointing to the roles of protein, vitamin D and antioxidant nutrients. The authors note that the loss of appetite and hunger response as a result of age causes on average a 25% decrease in food intake between the years of 40 and 70. This decrease in consumption not only leads to insufficient protein intake and also a low micronutrient status. Many vitamins and minerals play key roles in healthy muscular and neural functioning. Sayer and colleagues indicate that there is a four-fold increase in the likelihood of frailty in elderly populations with low vitamin D status, thus implicating the association with vitamin D insufficiency and sarcopenia. Interestingly, Sayer et al. note that meta-analysis (statistical analyses of multiple studies) indicate that vitamin D supplementation (700-1000 IU/day) reduces the risk of falls in older people.
It is clear to see that sarcopenia is a prevalent and debilitating disorder within the body with several causes, effects and counteractions. Moderate and high intensity aerobic exercise and resistance training can counteract neural decay and produce the antioxidants to fight the reactive oxygen species. This exercise program coupled with a proper nutritional plan provides a meaningful strategy that can make a difference in many cases between debilitation, or a healthy, active lifestyle. As personal trainers, it is our responsibility to see that the elderly we train are given the tools necessary to have the quality of life they have worked so hard to earn.
1. Does sarcopenia to a greater extent affect men or women?
There is no evidence to support gender specificity in sarcopenia. Sarcopenia is highly related to inactivity; those older adults with lower levels of physical activity are more likely to develop sarcopenia.
2. Is sarcopenia hereditary?
The onset of sarcopenia itself is not hereditary; however, many hereditary diseases and dysfunctions prevalent in later years may lead to a sedentary lifestyle and in turn sarcopenia.
3. What is the progression of muscle mass and strength loss with inactive persons?
After age 50, there is a progressive 1-2% loss of muscle per year. Muscle strength decreases by 3% each year after age 60 (Doria et al., 2012).
4. What foods should be consumed to best prevent and combat sarcopenia?
A diet rich in antioxidant containing foods such as fruits and vegetables is recommended (Doria et al., 2012).
5. Can older adults make muscle gains, or only slow the process of muscle loss?
With proper stimulus (resistance training) and adequate protein intake it is both possible and common for older adults to gain muscle.
6. What muscle fibers are most affected by sarcopenia?
It is worthy of note that sarcopenia has the greatest immediate effect on type II fast twitch glycolytic fibers as opposed to the type I slow twitch oxidative fibers (Doria et al. 2012).
7. How do I know if a person is a frail elderly?
Features of frailty are regular fatigue, inability to walk a block, and the incapacity to climb a flight of stairs. Frail individuals often suffer from several illnesses and loss of weight (Morely, 2012).
Doria, E., Buonocore, D., Focarelli, A., and Marzatico, F. (2012). Relationship between human aging muscle and oxidative system pathway. Oxidative Medicine and Cellular Longevity, Article ID 830257, 13 pages, doi:10.1155/2012/830257
Gomez-Cabrera, M.C., Domenech, E., and Vina, J. (2008). Moderate exercise is an antioxidant: upregulation of antioxidant genes by training. Free Radical Biology & Medicine, 44(2), 126-131.
Morley, J. E. (2008). Sarcopenia: diagnosis and treatment. Family Practice, 29, 144-148.
Sayer, A.A., Robinson, S.M., Patel, H.P, Shavlakadze, T., Cooper, C., and Grounds, M.D. (2013). New horizons in the pathogenesis, diagnosis and management of sarcopenia. Age and Ageing, 42: 145-150.
United Nations (2002). Political declaration and Madrid international plan of action on ageing. Second World Assembly on Ageing, Madrid, Spain.
U.S. Department of Health and Human Services (2008). Office of Disease Prevention and Health Promotion. 2008 Physical Activity Guidelines for Americans. www.health.gov/PAGuidelines/pdf/paguide.pdf
Ethan J. Harris is an undergraduate in Exercise Science at the University of New Mexico, Albuquerque. His research interests are anatomical dysfunctions and adaptations, protein metabolism and genetic variability. He plans on pursuing a Masters in Exercise Science.
Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at the University of New Mexico, Albuquerque, where he won the Outstanding Teacher of the Year award. He has received the prestigious Can-Fit-Pro Lifetime Achievement Award and American Council on Exercise Fitness Educator of the Year.