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), which can lead to sarcopenia. 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
People with low physical activity, unsuitable nutrition or conditions such as type II diabetes, cerebrovascular disease or osteoarthritis are more likely to develop sarcopenia (decreased muscle mass and strength), especially men.2.3 The consequences of decreased muscle mass include a marked increase in the risk of falls and fractures, and poor balance, decreased ability to walk, climb stairs, get up…1,4
Taking care of our muscles
Fortunately, there are interventions to limit the risks of sarcopenia and increase muscle 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 physical exercise is the most essential intervention, our nutrition also contributes to the composition (proportion of fat mass and dry mass), strength and volume of our muscles. As we age, our diet often changes. On the one hand, undernutrition and a reduction in proteins, vitamin D, antioxidants (carotenoids, flavonoids, vitamin E and C, selenium, etc) and polyunsaturated fatty acids are linked to the decrease in muscle functions. On the other hand, a diet rich in fruits and vegetables, providing vitamins and potassium, with a contribution of good fatty acids (eg fish oil, omega-3), can reduce acidity, inflammation and the oxidative stress of the body.8,9
Protein and amino acid intake is also essential, as our needs increase with age. Moroever, aged muscle cells react more weakly to amino acids to synthetize proteins.10 Current recommendations for adults are 0.8g/kg/day, i.e. 52g for a 65 kg person or 64g for 80kg. However, it’s often recommended that the elderly consume over 1.2g/kg/day, i.e. 72g for a 65 kg person or 96g for 80 kg. You can find 10g of protein in 300ml of yogurt, 1.5 eggs, 50g of meat or fish, 100g of tofu, 40g of nuts …
However, the proportion of some amino acids in protein intake is important. Leucine appears to play a particular role in stimulating muscle anabolism, as it is involved in regulating muscle protein synthesis.11 Leucine, unlike other amino acids such as valine or isoleucine, increases the availability of certain complexes necessary for protein production, by influencing their phosphorylation.12-14 It has even been shown that 6.25g of whey protein (the best source of protein for muscle synthesis15,16) combined with 5g of Leucine (therefore 11.25g in total) was just as effective as 25g of protein whey alone, especially after physical activity.17 Similarly, a dose leucine-enriched essential amino acids can increase muscle protein synthesis by 33% after physical activity compared to a normal dose of essential amino acids.18
Creatine is involved in the renewal of ATP. ATP is the main energy molecule of a cell and allows the muscle to contract. Thus, creatine intake will increase your energy levels and improve your athletic performance (intense and short) and recovery.19 Likewise, citrulline malate promotes aerobic energy production, displaces ATP to increase protein synthesis, reduces fatigue and promote recovery.20,21
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Food supplements should not be used as a substitute for a varied diet. The recommended daily allowance should not be exceeded. In general, food supplements are not suitable for pregnant and nursing women, children and adolescents. Keep out of reach of children.
- 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).
- Millward, D. J. Nutrition and sarcopenia: Evidence for an interaction. Proceedings of the Nutrition Society 71, 566–575 (2012).
- Robinson, S., Cooper, C. & Aihie Sayer, A. Nutrition and sarcopenia: A review of the evidence and implications for preventive strategies. Journal of Aging Research 2012, (2012).
- Cuthbertson, D. et al. Anabolic signaling deficits underlie amino acid resistance of wasting, aging muscle. FASEB Journal 19, 422–424 (2005).
- Xu, Z. R., Tan, Z. J., Zhang, Q., Gui, Q. F. & Yang, Y. M. The effectiveness of leucine on muscle protein synthesis, lean body mass and leg lean mass accretion in older people: A systematic review and meta-Analysis. British Journal of Nutrition 113, 25–34 (2015).
- Escobar, J. et al. Regulation of cardiac and skeletal muscle protein synthesis by individual branched-chain amino acids in neonatal pigs. American Journal of Physiology – Endocrinology and Metabolism 290, (2006).
- Norton, L. E. et al. The Leucine Content of a Complete Meal Directs Peak Activation but Not Duration of Skeletal Muscle Protein Synthesis and Mammalian Target of Rapamycin Signaling in Rats. The Journal of Nutrition 139, 1103–1109 (2009).
- Anthony, J. C. et al. Leucine Stimulates Translation Initiation in Skeletal Muscle of Postabsorptive Rats via a Rapamycin-Sensitive Pathway. The Journal of Nutrition 130, 2413–2419 (2000).
- Pennings, B. et al. Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men. American Journal of Clinical Nutrition 93, 997–1005 (2011).
- Kobayashi, Y. et al. Supplementation of protein-free diet with whey protein hydrolysates prevents skeletal muscle mass loss in rats. Journal of Nutrition and Intermediary Metabolism 4, 1–5 (2016).
- Churchward-Venne, T. A. et al. Leucine supplementation of a low-protein mixed macronutrient beverage enhances myofibrillar protein synthesis in young men: A double-blind, randomized trial. American Journal of Clinical Nutrition 99, 276–286 (2014).
- Pasiakos, S. M. et al. Leucine-enriched essential amino acid supplementation during moderate steady state exercise enhances postexercise muscle protein synthesis. American Journal of Clinical Nutrition 94, 809–818 (2011).
- Kreider, R. B. et al. International Society of Sports Nutrition position stand: Safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition 14, (2017).
- Bendahan, D. et al. Citrulline/malate promotes aerobic energy production in human exercising muscle. British Journal of Sports Medicine 36, 282–289 (2002).
- Goron, A. et al. Citrulline stimulates muscle protein synthesis, by reallocating ATP consumption to muscle protein synthesis. Journal of Cachexia, Sarcopenia and Muscle 10, 919–928 (2019).