(Or what happens to the muscle as we age and what should we do about it) 

It’s common knowledge that we deteriorate as we age.  When we are young, we don’t tend to think about getting old and life seems infinite and we feel invincible.  Which is great but bad because it isn’t conducive to looking after ourselves or making long term plans.  Most often by the time we get to an age where our body systems start to degrade, we have started to have the nagging feeling “I should be doing ‘stuff’ to look after my health/weight/how I feel, etc”.  Different body systems start to degrade at slightly different points in life, but from about 30 onwards it’s generally downhill. (☹).  But slowly. (😊).  In this write up I chat about the muscular system only, how and why it degrades, and what can we do about it.   

What is sarcopenia? 

Sarcopenia is the term used for age-related loss of muscle mass, strength and function.  This decline starts at about age 30.  We can naturally expect to lose 3% to 8% muscle mass per decade, depending on lifestyle factors.  After 60 this decline speeds up, and is a major cause and contributor to disability and loss of independence in the elderly as it can leave us weak and vulnerable to falls and injuries.  The decrease of bone density is linked to loss of muscle mass and lack of exercise, as is stiffness of joints, increase in body fat, loss of cardiovascular fitness.  These changes may lead to insulin resistance and diabetes, osteoporosis, heart disease and more.   Most men will loose about 30% muscle mass during their lifetimes.  American Society for Bone and Mineral Research reported in 2015 having found that people with sarcopenia had 2.3 times higher risk of a low-trauma fracture from a fall, such as a broken hip, wrist, arm, leg, or collarbone.  Research in the Journal of Epidemiology & Community Health suggests that the amount of lean muscle we have at middle age is linked to our risk of future heart disease.  Therefore, looking after our muscle mass in middle age may mean we are helping to reduce our chances of heart attacks and strokes later in life (British Medical Journal, Nov 2019).   

Why do we lose muscle as we age? 

The simplest answer to why we lose muscle is lack of use.  If you don’t use it, you lose it.  This is demonstrated by the fact that if we become ill and stay in bed for a few weeks doing sod all, the muscle atrophies (becomes smaller).  In the course of normal day we use our muscles to move and do things, keeping the muscle conditioned.  As we age, we tend to do less for all sorts of physical and lifestyle reasons.  As we do less, the muscle atrophies more, a vicious cycle. But the picture is much more complicated than just lack of use.  In muscle ageing many factors are involved, all of which aren’t completely understood but studies continue.  The following has been proposed so far.  Stem cells (cells that enable renewal) in the muscles decrease in numbers. the mitochondria (these make the energy in the cells) start to dysfunction and decrease in numbers, creatine phosphate and ATP stores (what is needed to make energy) within the muscle cell declines, muscle twitch time and twitch force (speed of the muscle response) decline.  Protein synthesis (muscle replacing old proteins) starts to decline, sarcoplasmic reticulum volume and calcium pumping capacity declines.   Sarcomere (muscle fibers) spacing becomes disorganised, muscle nuclei become centralized along the muscle fiber, the muscle’s plasma membrane becomes less exitable (less able to transmit messages), and fat accumulates around the muscle cells.  There is a decrease in the firing rate of the nerves to muscles, size of motor units increases, satellite cell number and recruitment changes. The metabolic changes in the muscle also has an effect on how much oxygen we are able to utilise during exercise (VO2max), so affect overall cardiovascular fitness.  Changes in the hormone levels and in the responsiveness to hormonal stimulus also affect the muscle *1*2.  Most important hormonal changes due to the ageing process are the drop of testosterone levels in men and the estradiol (one of the estrogens) levels in women, however mens muscle mass is more affected by these changes as testosterone facilitates the muscle protein synthesis.  Both sexes can equally suffer with an adverse effect on their bone density though.  Our response to nutrition also changes as we age, and muscle loss due to malnutrition can be caused by a diet that doesn’t adequately address the changing nutritional needs.  The muscles response to exercise also changes.  The ability of muscle cells to respond to increased insulin levels by increasing protein synthesis is impaired, which can lead to insulin resistance and diabetes.  It has been suggested this is actually due to changes in body composition and not the ageing process itself.  

What can we do to prevent muscle loss?  

1.Exercise 

Although the degradation described above is inevitable, we certainly need not resign to it.  In fact resigning to it will only serve to speed up the process.  Vive la resistance.  Most important and effective way to resist this process is exercise.  “Older people can indeed increase muscle mass lost as a consequence of aging,” says Dr. Thomas W. Storer, director of the exercise physiology and physical function lab at Harvard-affiliated Brigham and Women’s Hospital. “It takes work, dedication, and a plan, but it is never too late to rebuild muscle and maintain it.” (Harward Health Publishing, Feb 2016).  So activity not only prevents the sarcopenia caused by inactivity, it can reverse it and also many of the other effects on muscle associated with ageing.  Exercise is magic? 😉 . Both resistance (using weights and slow bodyweight movements to achieve load on muscles) and aerobic (faster movement resulting in elevated heart and breathing rate) exercise has been shown to be very useful.  Resistance exercise has been shown to increase muscle protein synthesis in people of any age as an immediate effect, and improve muscle strength, mass and function when repeated over time.  In people with certain existing health conditions resistance training can be more risky but a gentle start at appropriate level can be achieved. Aerobic exercise has been shown to improve VO2max, number and activity of mitochondria and insulin sensitivity.  It can also increase muscle protein synthesis as an immediate response to exercise, although may not induce obvious growth in muscle mass over time.  However, it may induce some in the muscles most used (usually legs), and will improve muscle function, strength and power.  Exercise program should be progressive for the maximum benefits (increasing in level of difficulty and load as we progress).  In Medicine & Science in Sports & Exercise 49 studies of men ages 50 to 83 who did progressive resistance training were analysed, and were found to have increased their lean muscle mass by 2.4 pounds.  For best results we should be doing both cardiovascular and resistance exercise as they have different benefits for the muscle.   

2. Nutrition 

As we age our protein requirements increase due to the declining ability to synthesise it.  As we age the metabolism slows down resulting in decreased hunger and often decreased food intake.  As our body composition changes (we pick up more body fat compared to muscle) we may decide to go on a low-fat diet for example, which may further reduce the amount of protein we consume.  If we then decide to introduce increased levels of activity into our routine, our muscles protein requirement increases further.  It has been shown in studies that supplementing the diets of older adults with essential amino acids (Proteins that we need to get daily from food) can increase the muscle mass even without exercise.  This can be achieved by taking an amino acid supplement which has no calories and therefore will not increase the calorie intake, or by taking traditional protein shakes which add calories, or by changing our diet to a more high protein one, not overlooking the need for micronutrients of course (vitamins and minerals).  Or a mix of those methods. For best results the protein intake should be evenly distributed over the day.  

3. Hormones?  

It has been shown that testosterone replacement therapy to normal levels in men results in a significant increase in muscle mass, strength, muscle protein synthesis and bone density.  Testosterone replacement therapy is not currently recommended for the treatment of sarcopenia though, and can have some unwanted side effects.  In women loss of muscle mass doesn’t seem to significantly increase when there’s a sudden drop of estrogen due to peri-/menopause, but estrogen replacement therapy is used for the symptoms of the perimenopause.  The estrogen treatment may in fact further decrease the muscle mass in women due to increasing serum steroid hormone binding globulin, thus resulting in lowered testosterone levels in women.  There have been some trials into treatments using growth hormone I axis and dehydroepiandrosterone, levels of which also decrease with age, but no clear benefits have been found and there are side effects.   

How to look after the middle-aged muscle and beyond 

Although the ageing process is inevitable, lifestyle factors make a huge contribution to how this process goes, specifically exercise and appropriate nutrition.  Diet should include adequate protein as well as be rich in micronutrients and at correct calorie level.  Exercise should include resistance training and cardiovascular training and be varied and challenging at the appropriate level. This will improve muscle mass and function, and also improve insulin resistance and other related issues.   

*1: Gillian Butler-Browne, Vincent Mouly, Anne Bigot, and Capucine Trollet, August 2018, In The Scientist 

*2 Elena Volpi, Reza Nazemi, Satoshi Fujita  Curr Opin Clin Nutr Metab Care. 2004 Jul. 

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