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A Diet High in Protein and Regular Physical Activity Can Combat Sarcopenia in Old Age

Although there is no universally accepted method of classification, sarcopenia generally refers to the loss of muscle with age. One approach to measure sarcopenia uses the skeletal muscle index. Ways of measuring muscle mass include magnetic resonance imaging (MRI), dual-energy X-ray absorptiometry (DXA), and bio-electrical impedance (BIA). Sarcopenia isn’t the only issue that comes with age, however. Fat volume tends to increase with age and can contribute to sarcopenic obesity.

There are a variety of consequences with sarcopenia. Loss of muscle strength, impaired physical function, and increased risk of falls, fractures, and dependence are just a few. Muscle atrophy may begin as early as 25 to 30 years of age. On average, 50% of men and 72% of women over the age of 80 are sarcopenic in the US. The average rate of muscle loss over age 70 is 1% per year.

Factors that contribute to the development of sarcopenia include hormones, protein balance, motor units, satellite cells, and fiber types. The body has two skeletal muscle fiber types: type 1 and type 2. Fast-twitch muscle fibers are deemed type 2. These muscle fibers have faster shortening velocity, develop greater tension, and are more easily fatigued. Sprinting is a physical activity that primarily involves type 2, fast-twitch muscle fibers. Slow-twitch fibers are deemed type 1. They are oxidative—meaning, they have a higher resistance to fatigue due to having more red blood cells that take up more oxygen.   The proportion of type 2 and type 1 muscle fibers are genetically determined. In young, healthy muscle, the diameter of the fibers is the same. With age, older adults experience a greater loss of type 2 fibers and a gain in type 1 fibers. Both factors are responsible for the loss in strength.

The loss of motor units with age also contributes to sarcopenia. Studies have shown that after the age of 60, the number of motor units declines and the average motor unit innervation ratio (the number of muscle fibers innervated by a single motor neuron) increases. These two factors suggest that neurons are lost with age and that existing motor units reinnervate the denervated fibers.

Satellite cells are muscle stem cells that lie dormant on the surface of the muscle fiber. These cells activate in response to injury and proliferate to the site of repair. They work together to regenerate the injured muscle. A study that explored satellite cells in elderly men and women aged 70 to 83 years compared to adults aged 20 to 32 years found that older women had 24% less satellite cells per muscle fiber than younger women. Moreover, older men had 37% less satellite cells per muscle fiber than younger men. This study’s results suggest that the loss of satellite cells lead to a loss of regenerative muscle function.

It is well known that exercise, specifically resistance training, can significantly enhance muscle mass in older adults, especially when paired with protein supplementation. Older adults in nursing homes and assisted living facilities are often frail and vulnerable to the consequences of sarcopenia. Care staff should encourage their patients to engage in appropriate resistance exercises with supervision, as well as provide patients with an appropriate diet high in protein in order to combat sarcopenia.