Our muscles fibres can become misshapen as we age, but resistance training seems to at least partially restore them, according to a study in about 200 people.
Some has reported misshapen muscle fibres in older people, so, to investigate, at Copenhagen University Hospital in Denmark and his colleagues looked back at samples they had taken from people’s thigh muscles for previous studies. These came from about 200 people aged between 20 and 97 who were largely physically inactive, but were deemed to be healthy and free of major medical problems.
The researchers gave the muscles fibres a score based on how much their cross-sectional shape deviated from a circle. Healthy muscle fibres deviate slightly because they have a pentagonal or hexagonal shape, and score about 1.2.
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Misshapen fibres may have an elongated or “squashed” shape, with extremely askew ones scoring around 1.9. For each sample, the scores of individual fibres were averaged to get an overall measure of misshapenness.
In the slow-twitch muscle fibres responsible for endurance activities, there was a small and gradual increase in misshapenness with age, the team found. In the fast-twitch muscles responsible for powerful movements, such as lifting weights, there was a much bigger increase, rising from 1.4 around age 20 to 1.6 by age 90.
The measure of misshapenness correlated with muscle performance as well or better than muscle size did, measured by the cross-sectional area of muscle fibres, says Søendenbroe.
He and his colleagues then got about 60 of the people to do at least three months of heavy resistance training three times per week. After a 5-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.
Afterwards, the researchers took further muscle samples and found a decrease in misshapenness in fast-twitch fibres in both younger (aged 20 to 36) and older (aged 60 to 80) volunteers. In the older group, the average score fell from around 1.5 to 1.45, for instance. The results have been posted to the bioRxiv preprint server, but aren’t yet peer reviewed.
The finding could help us understand more about the mechanisms through which strength increases, says at the University of Glasgow, UK. “I think they have shown nicely how the shape index does change with age,” he says. “But [on] the role of this in muscle function, I am less convinced, as we cannot establish cause and effect from this study.”
It is already clear from numerous other studies that doing resistance training can help people maintain muscle strength as they age and has many benefits.
“The earlier you start, [the better], but if you are in your 50s now, it would be a pretty damn good time to start doing something that can preserve muscle function for the remainder of your life,” says Søendenbroe. “You might live 40 years more, and if the last 20 years are characterised by low muscle function, meaning you are limited in what you do, that’s going to be 20 long years.”
bioRxiv
