570 skeletal striated muscles
Skeletal striated muscles bind bone through tendons. By contracting, they allow the voluntary movement of the skeleton in a specific direction. These contractions are controlled by motor neurons which connect the spinal cord and the muscles. Their activation leads to the release of calcium, which will bind to contractile proteins. Each muscle fibre (or myocyte, muscle cell) comes from the fusion of myoblasts, and contains between 2 and 500 nuclei at its periphery. It can no longer divide, but can increase its size by increasing the volume of the cytoplasm. Inside each muscle fibre, there are mostly myofibrils, which are the contractile units of muscle, composed of actin, myosin, troponin and tropomyosin.
Muscle mass loss with aging
Our muscles allow us to perform many movements and to mobilise our body, but also to maintain balance and posture, and to produce heat.
The muscle mass decreases with age and our strength decreases in parallel (from 10 to 15% per decade up to 70 years, from 25 to 40% after). Some metabolic changes greatly contribute to this decrease. Muscle protein breakdown is a normal physiological process, which is offset by the synthesis of new proteins in young people. As we age, protein synthesis decreases while protein degradation remains constant, resulting in reduced muscle turnover and reduced healing capacity. In addition, there’s a decrease in physical activity, a drop in hormone levels, some nutritional deficits, and chronic inflammation, which also contributes to the complex change in body composition.1
Taking care of our muscles
We can act to maintain and increase our muscular mass.
Resistance and endurance exercises
Our muscles are plastic and are fortunate enough to adapt to their demands throughout our lives. For example, some studies have shown that people between 60 and 80 years old, following an appropriate endurance training, can increase their aerobic capacity by 20 to 30%, which is like the performance of younger people. These performances are coupled with an improvement of the cardiovascular system and an adaptation of the peripheral muscles.1,5 Elderly people respond very well to resistance exercises too, which allow them to increase their strength and muscle mass. For example, weight lifting 3 times a week for 12 weeks allows people over 60 y.o to gain strength and increase the total muscle volume, similar to the performance of younger people…6 This phenomenon was also observed in nonagenarians, who, following adapted lower body training, could increase their strength, their mass and muscular functions, thus increasing their stability and walking speed and duration.7
Although exercise is the most important intervention, sufficient protein intake helps to maintain and increase muscle mass. Current recommendations for adults are 0.8g/kg/day, or 52g for a person weighing 65kg or 64g for 80kg. However, it is often recommended that older people consume more than 1.2g/kg/day, or 72g for a 65kg person or 96g for 80kg. 10g of protein can be found in 300ml of yoghurt, 1.5 eggs, 50g of meat or fish, 100g of tofu, 40g of nuts… In addition, calcium, magnesium and vitamin D contribute to maintaining normal muscle function.
This article is intended to summarize the basics of how a part of the human body works, but in no way replaces medical diagnosis and treatment.
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- Siparsky, P. N., Kirkendall, D. T. & Garrett, W. E. Muscle Changes in Aging: Understanding Sarcopenia. Sports Health 6, 36–40 (2014).
- Landi, F. et al. Prevalence and Risk Factors of Sarcopenia Among Nursing Home Older Residents. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 67A, 48–55 (2012).
- Sarodnik, C., Bours, S. P. G., Schaper, N. C., van den Bergh, J. P. & van Geel, T. A. C. M. The risks of sarcopenia, falls and fractures in patients with type 2 diabetes mellitus. Maturitas 109, 70–77 (2018).
- Landi, F. et al. Sarcopenia as a risk factor for falls in elderly individuals: Results from the ilSIRENTE study. Clinical Nutrition 31, 652–658 (2012).
- Seals, D. R., Hagberg, J. M., Hurley, B. F., Ehsani, A. A. & Holloszy, J. O. Endurance training in older men and women. I. Cardiovascular responses to exercise. Journal of Applied Physiology Respiratory Environmental and Exercise Physiology 57, 1024–1029 (1984).
- Frontera, W. R., Meredith, C. N., O’Reilly, K. P., Knuttgen, H. G. & Evans, W. J. Strength conditioning in older men: Skeletal muscle hypertrophy and improved function. Journal of Applied Physiology 64, 1038–1044 (1988).
- Fiatarone, M. A. et al. High-Intensity Strength Training in Nonagenarians: Effects on Skeletal Muscle. JAMA: The Journal of the American Medical Association 263, 3029–3034 (1990).