Our bodies begin to lose their muscle mass by roughly 0.5%-1% every year starting as early as our 40s and accelerates to 1%-1.5% decline per year in our 60s. By the age of 80, most individuals have lost upto 50% of their peak muscle mass. In a healthy body, new muscles are being built continuously and old muscles are being broken down continuously. Sarcopenia is a condition where the balance shifts towards muscle breakdown.
While muscle mass refers to mass of the muscle tissue, muscle strength is the ability of those muscles to exert force. The fact is, muscle strength declines much faster as we age – a condition known as dynapenia. Starting with 1% decline per year in our 40s, it accelerates to 1.2%-1.5% decline per year in our 50s and 60s and as much as 3%-4% per year in our 70s and beyond.
As one can imagine, muscle strength matters significantly more than muscle mass. Muscle strength, often measured through a metric such as ‘grip strength’ has been found to be a strong predictor of longevity even after adjusting for muscle size in various studies. Having said that, a minimum threshold of muscle tissue or muscle mass is necessary to build muscle strength. Hence, focussing on both – muscle mass and muscle strength is important, especially as we enter our 40s.
Leading causes of sarcopenia (loss of muscle mass) include:
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Hormonal Changes: When we are young, hormones such as testosterone, estrogen and growth hormones keep our bodies in build and repair mode. As the levels of these hormones drop, the body shifts from a state of building to a state of maintenance. Testosterone directly stimulates building of muscles – not just in men but also in women. Likewise, estrogen helps protect the muscles from inflammation and oxidative stress.
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Poor Nutrition: In your 20s, your body gets into a build muscle mode even with very little protein. However, as we age, to get the same trigger, we need to get much more protein in our diet. ~30g of protein per meal (20-40g depending upon your weight) is the recommended minimum for people above the age of 50 looking to retain their muscle mass and strength
Leading causes of dynapenia (loss of muscle strength) include:
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Neurological Factors: In the front of our brains, we have something known as a ‘motor cortex’. When we want to move any part of our body, it sends a signal down our spinal cord through motor neurons and from there into a nerve. A motor neuron takes the signal to the end of the nerve where it releases neurotransmitters which eventually cause the muscle to move. A motor neuron may be responsible for as little as 5 muscle fibres in our eyes and as much as thousands of them in our glutes.
As we age, the motor neurons in our body die. As a result, the muscle fibres it was incharge of become orphaned and the muscles lose the source of signal or power. However, when we do heavy resistance training, it forces the brain to leverage the remaining high power motor neurons enabling them to produce more force with fewer nerves.
Essentially, one of the ways in which you can age better while managing your muscle mass and muscle strength is (a) by focussing on your protein intake to build muscle mass and (b) by activating your motor neurons through resistance training to build muscle strength. Both are equally important as it is also possible to build muscle mass and yet have very low or poor muscle strength as per studies.
How can you measure your muscle mass and muscle strength ?
Tests to detect decline in Muscle Mass (Sarcopenia)
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DEXA Scan: Uses X-ray to measure your lean mass or skeletal muscle mass. A number below 15 kg in women and below 20 kg in men is considered a threshold. for sarcopenia as per European Working Group for Sarcopenia in Older People (EWGSOP). Typically recommended once every year to monitor age related decline
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Calf Circumference: If you do not have access to DEXA scan, a crude ‘proxy’ is calf circumference. If your calf circumference is less than 31 cm, it is a mark of sarcopenia.
Tests to detect decline in Muscle Strength (Dynapenia)
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Grip Strength: Measured with a handheld device known as dynamometer and squeezing it as hard as possible to measure your grip strength. A number less than 16 kg in women and a number less than 27 kg in men is generally considered as a cut off for dynapenia.
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Chair Stand Test: It helps measure your lower body strength and ability of your motor neurons to react quickly. How long does it take for you to stand up from your chair 5 times without using your arms. If it is more than 15 seconds, then you could be dealing with dynapenia
Sources:
National Library of Medicine, National Institute of Health (US) https://pmc.ncbi.nlm.nih.gov/articles/PMC4066461/
National Library of Medicine, National Institute of Health (US) https://pmc.ncbi.nlm.nih.gov/articles/PMC4112511/
National Library of Medicine, National Institute of Health (US) https://pmc.ncbi.nlm.nih.gov/articles/PMC2804956/
National Library of Medicine, National Institute of Health (US) https://pmc.ncbi.nlm.nih.gov/articles/PMC3571692/