The muscles, pillars of stability

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

Appropriate nutrition

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 synthesis^15,16) 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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