In this unique study, volunteers spent two weeks completely avoiding weight bearing on one leg to induce muscle atrophy.
After seven weeks of normal daily activity to allow recovery, the same leg was immobilised again for another two weeks.
Throughout the intervention, researchers measured muscle size, strength and molecular adaptations.
Now, the results are clear.
“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 Professor Adam Sharples.
The new findings show that young muscles recover well from periods of inactivity.
In older muscle, however, inactivity can leave a negative molecular memory that makes the muscles more vulnerable to future inactivity.
What is muscle memory, and why does it matter?
Muscle memory refers to molecular traces in your muscles that influence how they grow or shrink depending on previous experiences with exercise or inactivity.
Epigenetics describes mechanisms that can switch genes on or off without altering the DNA sequence itself.
These act like chemical “post it notes” on the DNA, and can persist long after exercise or inactivity, affecting how muscles respond later.
This research was funded by the Research Council of Norway.
Why this matters for older adults
Earlier studies have shown that muscles can remember resistance training performed earlier in life. Exercise leaves epigenetic marks that prime genes involved in muscle growth, helping the muscle regain size more efficiently after a break.
However, the new NIH study shows that muscles also remember periods of inactivity.
In young adults, this memory is mostly harmless: their 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.
In older adults, the opposite happens. The negative molecular signals are exaggerated when inactivity is repeated. This means that older muscles remember inactivity in a way that increases their vulnerability to future disuse.
Professor Sharples explains:
“Training in older age can still help to reverse or reduce many of these negative molecular signatures. 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.”
These findings are directly relevant for older individuals who have experienced falls or long periods without physical activity.
In these cases, exercise training helps the muscles adapt and recover, potentially preventing a downward spiral of continued muscle loss.
What this means for young people
For younger adults, the story is more positive.
Exercise creates a beneficial molecular memory that helps muscles regain strength and size more quickly after a break. Several genes in young muscle remain epigenetically primed to support growth, even after periods of inactivity.
Young muscles also showed resilience during repeated disuse: the same genes were less affected the second time.
Sharples’ three recommendations for strong lifelong muscle memory
- Start resistance or high intensity exercise training as a young adult
This likely builds a beneficial buffer for later in life. It is never too late to start, and training even at older ages can reduce the molecular age of your muscles.
- Break up periods of inactivity
Repeated inactivity can leave long lasting molecular marks. If you are injured or unable to train, try to maintain some activity such as walking or simple mobility exercises. Follow a progressive resistance training programme once you recover.
- Stay consistent to protect ageing muscles
Avoid long inactive periods when possible. Regular movement helps maintain healthier molecular patterns in muscle.
Reference:
Repeated Disuse Atrophy Imprints a Molecular Memory in Skeletal Muscle: Transcriptional Resilience in Young Adults and Susceptibility in Aged Muscle https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202522726