When it comes to muscles, the phrase ‘use it or lose it’ applies perfectly.
And the good news, according to University of Otago and Brain Research New Zealand neuroscientist Phil Sheard, is that even a modest amount of exercise is enough to stave off muscle weakness and frailty in old age.
'Use it or lose it.' Even modest amounts of weight-bearing exercise will slow down muscle wasting as we age. Photo: 123RF
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If you are in your twenties, the good news is that your muscles are probably the strongest they’ll ever be.
Muscles are at peak performance in our 20s, and decline in strength as we age. Photo: CC BY-SA 2.0 University of Liverpool
The bad news is that it is downhill from there in terms of muscle strength. Even if you work out, by the time you get to your fifties you are losing 1-2 percent of muscle mass per year.
Of course, if you haven’t exercised at all, then you’ll have already lost a lot of muscle mass as individual muscle fibres atrophy or wither.
Muscle weakening is a process called sarcopenia, literally ‘poverty of the flesh’, and it is a major cause of frailty amongst the elderly.
Why that matters, says Phil Sheard, is that “as we get older, the main driver for transitioning from independence to dependence is frailty. Frailty encompasses many things, but the major one is musculoskeletal weakness, which is deterioration of the bones and the muscles.”
Muscle weakness may make it hard to get up out of a chair, or carry the shopping – or it could lead to a fall.
The importance of the nervous system
People have always assumed that weakness is a result of changes to the muscle, but Phil’s recent research with laboratory mice has shown that changes to the muscle are caused by something else.
“A major driver of muscular weakness is nerve deterioration,” says Phil.
Each muscle fibre, Phil explains, is connected to the nervous system – which is collectively the nerves, spinal cord and brain - at a single point called a neuromuscular junction. Each nerve in the spinal column provides input to many muscle fibres. What happens over time is that increasing numbers of muscle fibres lose their connection to a nerve. As a result they no longer work and they start to shrink.
Early on in the process says Phil, it is possible for some muscle fibres to reconnect to a different nerve, but we lose this ability as we age.
“Between being young and elderly, about 20 percent of the cells in the spinal cord that make direct contact with muscle fibres and that are responsible for activating muscle fibres, die. And that means that about 20 percent of muscle fibres will have lost their input.”
Exercise is good
Phil says that he has also investigated the impact of exercise on muscles. He reports that mice that exercise regularly have better muscles, healthier neuromuscular junctions and they lose fewer nerves in the spinal cord.
“What is it that exercise is doing? We know that active muscles make substances called nerve growth factors or neurotrophins, in amounts that are proportional to the way they are used. So a very active muscle makes more of some kinds of nerve support substances than a not very active muscle.”
“The ‘use it or lose it’ phrase actually has a biological basis,” says Phil. “Muscle fibres actually respond to being used, by providing food to the nerve cells that provide their activation.”
“The clear message is that being active will do things to your nerves and muscles to allow you to be active. The more you do, the more you’ll be able to do – and the longer you’ll be able to do it for.”
And the best news of all is that it doesn’t take much.
“Those who do a little bit get almost as much benefit as those who do a lot.”
