Aging Muscles May Be Trading Strength for Survival

Key takeaways

• Researchers found that cardiolipin, a fat molecule essential to mitochondrial function, declines in aging muscle in both mice and humans.

• Lowering cardiolipin in young mice triggered a shift from powerful fast-twitch fibers toward slower, more fatigue-resistant fibers.

• That shift appeared to protect stressed muscle cells—not simply reflect deterioration. Giving affected mice antioxidants interfered with the response and made their muscles fare worse.

• Partially restoring cardiolipin began reversing muscle wasting in mice. Whether this approach can preserve strength in aging people remains unknown.

A weaker muscle may be defending itself

What looks like decline may sometimes be an attempt to survive.

That is the unexpected finding from research led by the University of Copenhagen. The study suggests that when mitochondria become stressed, muscle cells can sacrifice some of their power to protect themselves from further damage.

The discovery helps explain a longstanding puzzle: why aging muscles increasingly favor slow-twitch fibers, even though these fibers depend heavily on mitochondria that are becoming less efficient.

The problem starts in the membrane

Mitochondria need more than fuel. They also need the right structure.

Cardiolipin helps maintain the folded inner mitochondrial membrane, where much of the machinery for energy production operates. When this specialized fat becomes scarce, mitochondrial structure and function suffer.

Researchers found lower cardiolipin levels in aging muscle from both humans and mice. To test whether the decline could drive changes rather than merely accompany them, they reduced cardiolipin in young mice.

The animals developed a pattern resembling aging muscle: fewer fast-twitch fibers and a greater proportion of slow-twitch fibers.

Why the switch may be protective

Mitochondria lacking cardiolipin produced more reactive oxygen species, or ROS—molecules that can damage cells but also signal that something needs to change.

That signal helped activate a response coordinated by a protein called ERRγ. Muscle cells changed their fiber characteristics and redirected resources toward defending themselves.

The affected muscles absorbed more glucose, but they were not primarily using the extra sugar for energy. Instead, they diverted it toward producing their own antioxidants.

The result was a trade-off: less explosive power, more protection against cellular stress.

When antioxidants made things worse

One of the most revealing experiments challenged the assumption that removing more ROS is always beneficial.

Giving affected mice antioxidants reduced the signal driving the protective adaptation—and their muscles fared worse.

That does not mean antioxidant-rich foods harm muscle or that all antioxidant supplements have the same effect. It shows that, in this experimental setting, suppressing a stress signal also disrupted the response helping cells cope.

The distinction matters: a damaging molecule can also carry useful information.

A partial repair with a striking result

Restoring cardiolipin to approximately two-thirds of its normal level began reversing muscle wasting and prevented the premature deaths seen in the affected mice.

That is encouraging, but these were animals with experimentally disrupted cardiolipin—not a trial showing rejuvenation in normally aging people.

Human muscle samples established that cardiolipin also declines with age. The experiments demonstrating protection and reversal were conducted in mice and laboratory-grown cells.

The takeaway

This study suggests that some age-related muscle changes may be defensive adaptations rather than straightforward failures.

The therapeutic challenge is therefore more subtle than forcing muscle fibers back into a youthful pattern. It may require repairing the underlying mitochondrial problem while preserving the responses that keep stressed cells alive.

References:

1. Fabian Finger, Mikkel Frost, Shinya Watanabe, Tao Ma, Taewook Kang, Dipsikha Biswas, Ruben Zapata-Perez, Vincent Anton, Lucile Dollet, Lasse K. Markussen, Nanami Senoo, Iuliia Karavaeva, Astrid Linde Basse, Oksana Dmytriyeva, Tara TeSlaa, Jesper F. Havelund, Amy M. Ehrlich, Marta Moreno-Torres, Caio Yogi Yonamine, Nicoline R. Andersen, Ida Blom, Francisco Garcia-Carrizo, Piyarat Siripoksup, Magnus Asping, Thomas S. Nielsen, Marcus Nygård, Anders B. Klein, Andrey Tvardovskiy, Trine S. Nicolaisen, Carlos Durantez-Fernández, Klaus Qvortrup, Clara Prats, Joshua D. Rabinowitz, Christoffer Clemmensen, Lykke Sylow, Juleen R. Zierath, Jonas T. Treebak, Tim J. Schulz, Trisha J. Grevengoed, Steven M. Claypool, Julien Prudent, Rob C. I. Wüst, Susanne Mandrup, Riekelt H. Houtkooper, Kei Sakamoto, Nils J. Færgeman, Martin R. Larsen, Katsuhiko Funai, Steen Larsen, Zachary Gerhart-Hines. Mitochondrial membrane lipid cardiolipin controls fiber-type adaptations in aging muscle via estrogen-related receptor γ. Nature Aging, 2026; 6 (10): 2092 DOI: 10.1038/s43587-026-01227-7