Scientists in the United States say they may have found a way to give new life to jaded muscles.
The findings could one day help injured athletes
Researchers at Stanford University in California have been able to rejuvenate muscles in mice.
By manipulating molecular signals, they have given relatively elderly mice youthful muscles.
Writing in the journal Science, they said the findings could one day be used to help injured athletes or even people with muscle wasting diseases.
It may also help scientists in their quest to find ways of fighting aging.
Longer to heal
Injured muscles take longer to heal when people and animals for that matter get older.
For years, scientists have thought that this is because the cells needed to regenerate muscle tissue die as the years go on.
However, this latest study suggests otherwise. Dr Thomas Rando and colleagues have discovered that the problems are caused by impaired molecular signalling.
But they have also found that this fault can be corrected and that muscles can be rejuvenated.
The research focused on signals that stimulate "satellite" cells dotting the outside of muscle fibres.
These cells come to the rescue of damaged muscle, dividing to form new muscle tissue and generating more satellite cells for future repairs.
Although the scientists looked at the ability of injured tissue to heal, they expect the same principle to apply to natural muscle loss through ageing.
Dr Rando said: "If you presume that normal muscle bulk is maintained by gradual replacement of muscle tissue by satellite cells and that gradual replacement is diminished in older people, that would lead to atrophy.
"Figuring out atrophy in one of the pathways could relate to the others."
Previously, Dr Rando's team found that satellite cells are activated by a cell protein "switch" called Notch.
What flicks the switch is another protein called Delta, which is made on
nearby cells in injured muscles.
The scientists found that mice with an age equivalent to that of 70-year-old
humans made much less Delta after an injury than younger mice. As a result,
fewer satellite cells were activated to repair muscle damage.
However, the scientists showed that when a Delta-mimicking molecule was applied to injured older muscles they could rejuvenate.