If you’re working hard to build strength and muscle size, the thought of losing it is, well, a little disconcerting! Loss of muscle not only impacts body composition but functionality as well. The reason many elderly people have limited ability to do the things they enjoy is that their muscles have lost size as well as strength and power. In fact, age-related loss of muscle size is a growing epidemic among the aging population.
This age driven loss of skeletal muscle is called sarcopenia. Not only can sarcopenia affect the ability to get around, but it can also cause problems like excessive fatigue. If you don’t have as much metabolically active muscle, you have less stamina. Plus, as muscle tissue declines, fat storage increases, creating an unhealthy body composition and a slower metabolism. As you lose muscle strength and mass, you’re also more prone to falling and possibly fracturing a hip, a potentially life-threatening injury. Whatever we can do to stave off this problem is vital for long-term good health.
The Saga of Muscle Size Loss
The reality is muscle loss begins early in life. You typically reach your peak of muscle mass, assuming you’re sedentary, by your mid-30s. People who don’t strength train and are inactive lose around 4% of their total muscle mass each decade after age 30 and the process speeds up after the age of 50. Have you ever wondered why you lose muscle as you grow older and what you can do about it? Let’s look at four changes that happen with age that lead to sarcopenia.
Motor Units Remodel
The skeletal muscles in your body are innervated by motor units. A motor unit consists of an alpha motor neuron, a nerve cell that carries signals from the brain and tells the muscles to contract, as well as the muscle fibers it innervates. As you age, these motor units remodel and you lose some of them. In fact, a study showed that by age 70, even healthy people have lost about 40% of their motor units.
Most of the motor units lost innervate fast-twitch muscle fibers, ones involved in strength and power movements. Motor units that connect to slow-twitch, or endurance, muscle fibers actually enlarge somewhat to compensate. This partially explains why you lose strength more than endurance as you age. You have fewer motor units innervating the strong, powerful fast-twitch fibers and fewer fibers. The muscle itself also remodels and accumulates more fat and connective tissue relative to muscle fibers.
Decreased Muscle Protein Synthesis
Another factor that contributes to muscle loss with age is a reduction in muscle protein synthesis. Muscles tissue is constantly breaking down and rebuilding, a phenomenon known as muscle turnover. With age, net muscle protein synthesis goes down. One reason this happens is that older muscles develop some degree of anabolic resistance. In other words, they become less responsive to anabolic stimuli such as dietary protein and, to some degree, the effects of resistance training.
When anabolic resistance sets in, you may need more dietary amino acids from protein to optimize muscle protein synthesis. The branched-chain amino acids, particularly leucine, are the strongest stimulators of muscle protein synthesis. Getting more leucine-rich foods may help turn on sluggish muscle protein synthesis related to aging. In support of this, a study showed that leucine supplementation in older adults boosted the synthesis of muscle protein. Some studies also show that omega-3 supplementation may counteract anabolic resistance and reduce muscle loss. In addition, research suggests that high-intensity resistance training may be more effective for overcoming anabolic resistance than high-volume, low-resistance training.
Hormonal Changes
Hormonal changes are also key players in muscle loss and sarcopenia. Women, after menopause, have lower levels of anabolic hormones, like testosterone, growth hormone, and IGF-1. These are hormones that ramp up the synthesis of new muscle proteins. Inflammation also increases with age and there’s evidence that inflammation is a contributor to muscle catabolism or breakdown. Cortisol also rises and this has a further catabolic effect on muscle.
Decreased Physical Activity
One of the major contributors to sarcopenia is physical inactivity. It’s the classic case of “use it or lost it.” Adults who don’t resistance train are destined to lose even more muscle size and strength with age than those who pump iron. The good news is there’s something you can do about it – train! Age doesn’t seem to be a factor as far as whether muscles respond to training. How do we know this?
One study found that elderly men gained muscle size and strength after only 3 months of strength training. Due to anabolic resistance, the way to optimize gains is to use a heavy resistance and make sure you’re consuming enough protein. Older adults, especially physically active ones, can benefit from more protein than younger people, as much as twice the amount, depending on the intensity and frequency of training. Some research shows that a dose of 20 to 30 grams of protein after a workout is beneficial for older adults.
The Bottom Line
Unfortunately, we do lose muscle mass and strength with age – and now you know why. Fortunately, lifestyle can counteract much of this loss. The most important deterrent to muscle loss in later life is heavy resistance training combined with a diet higher in protein, particularly the amino acid leucine. Most older people get too little exercise and not enough protein. In addition, increasing the amount of dietary omega-3 may also offer some additional benefit in the fight against anabolic resistance. Sleep and stress management are part of the equation too! Stress or poor-quality sleep elevates the catabolic hormone cortisol and enhances muscle loss.
References:
WebMD. “Sarcopenia with Aging”
Biogerontology. June 2016, Volume 17, Issue 3, pp 485–496.
Nutr Metab (Lond). 2011; 8: 68. Published online 2011 Oct 5. doi: 10.1186/1743-7075-8-68.
Clin Nutr. 2012 Aug;31(4):512-9. doi: 10.1016/j.clnu.2012.01.005. Epub 2012 Feb 20.
International Journal of Endocrinology. Volume 2012 (2012), Article ID 127362, 10 pages http://dx.doi.org/10.1155/2012/127362.
J Gerontol A Biol Sci Med Sci. 1995 Nov;50 Spec No:11-6.
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