Keeping muscle fibre in shape helps us keep in shape, too

Oh the joys of getting older! Now that I’ve reached my upper 50s, I’m continuing to discover little variations to all parts of my body. Hair sprouts feverishly from my ears. I have a lovely new skin tag on my eyelid. And my nose – has it changed shape? It might not be the only thing to do so. New research suggests that our muscle fibres also become misshapen as we age.

At least our muscle fibres aren’t visible to others! Thank goodness for small mercies. But is a change in shape in muscle fibre anything to be concerned about? It’s an interesting question.

Medical scientists have known for a long time now that as we age, our muscles undergo changes. None of these are any good, sadly. First, muscle fibres reduce in number and shrink in size. Second, muscle tissue is replaced more slowly, and lost muscle tissue is replaced with a tough, fibrous tissue. And to complete the hat-trick, changes in the nervous system cause muscles to have reduced tone and ability to contract.

Now, thanks to Casper Søendenbroe at Copenhagen University Hospital in Denmark and his colleagues, we can add a fourth change.

Muscle fibre – the bad news

Søendenbroe’s team were aware that age-related loss of strength is disproportionally greater than the loss of mass. So they decided to follow up on research done in 2020 which pointed towards muscle fibre deformity. To do so they looked back at samples they had taken from people’s thigh muscles for previous studies.

Their sample took in nearly 200 people whose ages ranged from 20 to 97. The cohort was largely inactive, but otherwise healthy and free of medical issues.

Using what they call the Shape Factor Index (SFI), the researchers ‘scored’ two types of muscle fibre – fast-twitch and slow-twitch. The athletes among you might recognise the types. Slow-twitch muscle fibre is associated with endurance, while fast-twitch fibre is useful for powerful bursts, such as when weightlifting.

Misshapen fibres may have an elongated or “squashed” shape. Søendenbroe’s SFI method means that the more misshapen the muscle fibre is, the higher the score is assigned. Extremely askew ones, for example, score around 1.9, while healthy muscle fibres score about 1.2.

It was the fast-twitch fibre in which the researchers found the greater change. While slow-twitch muscle showed a small and gradual increase with age, fast-twitch fibre displayed a much bigger increase. Scoring around 1.4 at age 20, the SFI rose to 1.6 by age 90.

Is there any good news?

Yes, there is, and it comes out of the same research. As part of their study, Søendenbroe’s team got about 60 of the people to do at least three months of heavy resistance training three times per week. After a five-minute cycling warm up, the participants did between three and five sets of leg presses, leg extensions, leg curls and two optional upper-body exercises, with up to 15 repetitions per set.

The good news? At the end of the three months, follow-up muscle fibre samples showed a decrease in misshapenness in fast-twitch fibres. Even better, this improved SFI occurred in both younger and older volunteers. In the older group (aged 60 to 80), the average score fell from around 1.5 to 1.45.

One thing to be mindful of is that this study is still in what’s known as the preprint stage. That basically means it has not yet been peer reviewed.

Notwithstanding that, it appears to support the notion of which most of us were probably already aware: your best chance of keeping your muscles in shape is to keep using them.

The old adage, ‘Use it or lose it’, rings true once more.

Have you made a concerted effort to keep your muscles in shape as you age? What exercises do you do? Let us know via the comments section below.

Also read: Heavy drinkers risk loss of muscle mass

Health disclaimer: This article contains general information about health issues and is not advice. For health advice, consult your medical practitioner.

Andrew Gigacz
Andrew Gigacz
Andrew has developed knowledge of the retirement landscape, including retirement income and government entitlements, as well as issues affecting older Australians moving into or living in retirement. He's an accomplished writer with a passion for health and human stories.


  1. No kidding , it’s called ageing. From the age of mid 30s we are slowly rotting away. Unless you get run over by a truck , fall off a cliff etc….you will eventually rot away .
    Body organs throw in the towell , teeth fall out, hair falls out, memory goes & in the end it all just stops & they dig a hole.
    Regular exercise , a healthy diet & fun attitude to life will make that journey a bit more pleasant.
    Enjoy the ride.

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