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Bittersweet Sarcopenia

  • 10/17/2011 5:28:00 PM
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Bittersweet Sarcopenia

Nina Laidlaw Rumler, B.A.

You might not have heard of sarcopenia, but it touches everyone – everyone who lives long enough to undergo this normal physiological process. A lessening of muscle mass and function, its cumulative effect is becoming a significant public health concern. Two factors contribute: lessened physical activity and increased longevity, eventually resulting in frailty in the elder years.
The word means "poverty of flesh," a pitiful image. Age-related, it is the degenerative loss of skeletal muscle mass and function (muscle cells becoming both fewer and smaller), with a 0.5 to 1% loss per year. The process is generally believed to begin after the age of 40, although some suggest it starts as early as 25 years of age.
In other words, by simply staying in place in terms of muscle strength, we’re losing ground as we age. If something limits activity – i.e. a sedentary job, an injury, or illness – that reduction in muscle mass and power might worsen. Then yard work or sports or other discretionary physical activities might be dropped, to add to the effect. Figure in our longer lifetimes as well as the effects of other age-related conditions (such as osteoporosis), and it is easy to understand projections of significant frailty in the elderly.
Glum enough now? See yourself in any of the above scenarios? Well, cheer up, at least a little. Although aging and its effects are a reality, exercise helps. Research has found that exercise, even simple increases in activity, slows down the effects of sarcopenia. Numerous studies have shown that elderly exercisers can retain or possibly regain strength and muscle function. A gradually increasing exercise program, combining both aerobic and resistance training, is considered the best strategy. Resistance training is particularly important, as reported repeatedly in research.  Muscle loss is higher in the fast-twitch (FT) fibers that are most important in high-intensity, anaerobic movements.
However, although the effects of sarcopenia are seen more in the physically inactive, active individuals suffer also. This finding suggests that there are contributing factors besides physical inactivity, which include decreased hormone levels, motor-unit remodeling, and decreased protein synthesis. For just a bit of detail on these factors, hormones that decrease with age include growth hormone (GH), testosterone (T), and insulin-like growth factor (IGF-1), which are associated with protein metabolism, maintenance, and synthesis. Research findings are inconsistent as to whether hormone replacement (mainly GH) is effective in maintaining or gaining muscle mass.
“Motor-unit remodeling” has to do with the neurons that activate the muscles. The motor unit is a single neuron and the muscle fibers it activates. Remodeling, like sarcopenia, occurs in everyone and refers to an irreversible loss in the number of spinal cord motor neurons and functioning motor units. Remodeling describes the process in which neurons that activate FT muscles die and nearby slow twitch (ST) neurons take over activating those muscles. However, the remodeled motor unit will provide weaker and slower movements with less precise control of movements.
The body continually balances protein synthesis with protein breakdown to provide what is termed “whole-body protein turnover.” The turnover rate changes with age, reflecting a decreased synthesis rate rather than a higher breakdown rate, so less muscle protein is produced. A decrease in muscle protein synthesis will result in the loss of muscle mass. This slowdown affects not only the amount of protein and muscle mass but the recovery rate after injury or over-exercise.  Resistance exercise is believed to improve synthesis.
Although these might be bitter facts, the sweet part is that resistance exercise has a huge effect. Another is you are likely young enough to protect your strength in your later years by acting now.

Further reading:

  1. Hasten DL, et al. Resistance Exercise Acutely Increases MHC and Mixed Muscle Protein Synthesis Rates in 78-84 and 23-32 yr olds. American Journal of Physiology. 2000;278:620-626.
  2. Peterson MD & Gordon PM. Resistance exercise for the aging adult: clinical implications and prescription guidelines. American Journal of Medicine. 2011;124:194–198.
  3. Roth SM, Ferrell RF, Hurley BF. Strength training for the prevention and treatment of sarcopenia. Journal of Nutrition, Health & Aging. 2000;4(3):143-55.
  4. Waters, DL, Baumgartner RN & Garry PJ. Sarcopenia: Current Perspectives. Journal of Nutrition, Health & Aging. 2000;4(3):133-139.



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