Inactivity can leave lasting marks on your muscles

For several weeks, the particiants in this unique study pretended they were injued.

First they avoided any weight bearing on one leg for two weeks.

The goal was to trigger muscle loss, also called muscle atrophy. 

After seven weeks of normal daily activity to allow recovery, the same leg was immobilised again for another two weeks. 

Along the way, the researchers followed them closely. They measured how much muscle strength they lost and how much smaller the muscles became.

Now the researchers have clear answers.

Clear difference between young and old

“Our earlier work showed that regular exercise leaves a positive molecular memory in your muscles, something that may help them adapt more effectively after a break,” says Adam Sharples.

He is a professor at the Norwegian School of Sport Sciences' Department of Physical Performance.

The new findings show that young muscles recover well from periods of inactivity. 

For older people, however, inactivity can lead to molecular marks that may make your muscles more vulnerable to future inactivity, the professor explains.

Can be preventative for older people

Earlier studies have shown that muscles 'remember' strength training – also called resistance training – performed earlier in life. 

Exercise leaves epigenetic marks in the muscles. These activate the genes involved in muscle growth, helping the muscle regain size more efficiently after a break.

Sharples' newest study shows that muscles also remember periods of inactivity.

What this means for young people

Exercise creates positive muscle memory that helps muscles regain their strength and size more quickly after a break. 

Several genes in young muscle remain epigenetically primed to support growth, even after periods of inactivity.

The researchers see that young adults' muscles recover well and show a protective molecular response during repeated periods of disuse. Some of the genes affected by inactivity become less sensitive the second time around.

Why this matters for older adults

In older adults, the musculature appears to be more vulnerable. Negative changes seem to be stored in muscle memory. Older muscles remember inactivity more negatively than young muscles do. 

Nevertheless, Sharples explains that working out can still help reduce or even reverse these memory traces in both young and older people.

“A structured training programme after illness or injury can support muscle regrowth, and this is just as important later in life as it is when you are young,” the professor says.

The muscles become more vulnerable with a negative memory in older age, which underscores the importance of early prevention and more continuous training periods.

These findings are directly relevant for older individuals who have experienced falls or long periods without physical activity. 

In these cases, exercise helps the muscles adapt and recover, potentially preventing a downward spiral of continued muscle loss.

Three tips for strong lifelong muscle memory

Sharples has three tips on how you can build strong muscle memory:

1. Start strength training or high intensity training as a young adult

This likely builds a beneficial buffer for the future. But it's never too late to start – even exercising at older ages can reduce the molecular age of your muscles.

2. Break up periods of inactivity

Repeated inactivity can leave lasting molecular marks. If you are injured or unable to train, try to maintain some level of activity, such as walking or simple mobility exercises. Follow a progressive resistance training programme once you recover.

3. Stay consistent to protect ageing muscles

Avoid long inactive periods when possible. Regular movement helps maintain healthier molecular patterns in the muscles.

Reference:

Turner et al. Repeated Disuse Atrophy Imprints a Molecular Memory in Skeletal Muscle: Transcriptional Resilience in Young Adults and Susceptibility in Aged Muscle, Advanced Science, 2026. DOI: 10.1002/advs.202522726

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Read the Norwegian version of this article on forskning.no

About the research

The research is funded by the Research Council of Norway.

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