Abstract
Two major studies published in 2026 converge on the same tissue. A Nature Medicine study of 60,542 people built aging clocks for more than forty different cell types and found that they age at different rates within the same person — and that of all of them, accelerated aging of skeletal muscle cells was the single strongest predictor of death from any cause, ahead of brain, heart, and every other tissue. A Nature Aging study then explained what muscle aging is at the molecular level, using a cohort designed to separate aging from inactivity: its defining signature is an energy crisis (declining mitochondrial genes, falling NAD⁺, fat accumulating inside muscle), and while structured training erased about half of the age-related molecular changes, the other half persisted regardless of training — concentrated in nerve-to-muscle communication and stem cell/tissue-maintenance signaling. Together the two studies make one case: muscle is the tissue that most predicts survival, and half of its aging cannot be exercised away. This article explains both findings for anyone who fears frailty, and describes the therapeutic approaches at Blast Institute aimed at that persistent half: pluripotent stem cell therapy and PSC-derived exosomes, Follistatin (FST-344) gene therapy, and LAV-BPIFB4, a longevity-associated gene variant with published human evidence linking it to reduced frailty. Exercise remains essential and irreplaceable. It is simply not, by itself, sufficient.
Ask most people how to keep their strength into old age and you will get the same answer: use it or lose it. Keep moving. Stay active. It is good advice, and it is true as far as it goes. The trouble is that it has quietly persuaded a great many people of something false — that frailty is essentially a discipline problem, and that anyone who keeps walking has nothing to worry about.
Two studies published in 2026 complicate that comfortable picture, and they do it from opposite directions. One tells us how much muscle matters — more, it turns out, than any other tissue in the body. The other tells us how much of muscle aging we can actually control through effort. Read together, they deliver a message that is at once sobering and clarifying, and that points directly at what medicine, rather than willpower, will need to do.
The Stakes: Muscle Predicts Survival More Than Any Other Tissue
Begin with the question of why muscle deserves special attention at all. The answer comes from one of the largest aging studies yet conducted, published in Nature Medicine in 2026.
The researchers took blood from 60,542 people and measured more than seven thousand proteins, then traced those proteins back to the specific cell types that produce them — brain cells, muscle cells, lung, gut, immune, bone marrow, and more. Using machine learning, they built a separate biological-age clock for each of more than forty distinct cell types.
The first finding is startling on its own: your cell types do not age in synchrony. Within a single person, muscle may be a decade older than liver while immune cells stay young and brain support cells race ahead. Aging, at the cellular level, is not one clock but dozens, running at different speeds. Between one and three percent of people had ten or more cell types aging rapidly all at once.
These clocks were not merely descriptive; they were predictive over fifteen years of follow-up. Rapidly aging astrocytes — the support cells of the brain — flagged future Alzheimer’s disease about as strongly as the highest-risk Alzheimer’s gene. Rapidly aging muscle cells flagged ALS more than three years before diagnosis. Aging airway cells compounded the lung-cancer risk of smoking.
Accelerated aging of skeletal muscle cells was the single strongest cellular predictor of all-cause mortality in the entire study, followed by neurons, fibroblasts, and others. Put plainly: if you want to know how long someone is likely to live, the aging of their muscle tells you more than the aging of any other tissue measured.
This is worth pausing on, because it inverts a common assumption. We tend to think of muscle as a matter of strength or appearance, and of the heart or brain as the organs that determine survival. This study says otherwise. And it carries a second, more hopeful implication: muscle is also among the most modifiable tissues in the body. The strongest death-predictor we have identified is also one of the ones we have the most power to influence. The study cannot prove that training or any therapy rewinds this particular clock, and we will not claim it does. But muscle loss tracks mortality in every population it has been measured in, and the protein signatures behind this clock are tied to how muscle is built and how well it produces energy.
One caution, stated plainly: this is a research finding from banked blood in a cohort skewing older and predominantly white, not a test available for purchase, and the authors themselves call for validation in younger and more diverse populations. It tells us where to look. It does not yet tell any individual their number.
So muscle is the tissue to defend. The natural next question is how much of its aging we can defend against — and that is where the second study comes in.
The Mechanism: What Muscle Aging Actually Is
If muscle is the tissue that most predicts survival, the practical question becomes what muscle aging actually consists of, and how much of it we can change. A second 2026 study, published in Nature Aging, answers both with unusual precision — and its central result puts a humbling number on how far the familiar advice to “stay active” really goes. The answer, roughly, is half.
Almost every previous study of exercise and aging has been confounded by the same problem. Older people, on average, move less than younger people. So when researchers find molecular differences between young and old muscle, they cannot say whether they are looking at aging or simply at decades of reduced activity.
Researchers at Amsterdam UMC and Maastricht University addressed this with careful cohort construction. They recruited young adults in their twenties, and then recruited older adults whose daily step counts and time in high-intensity activity actually matched the young group. Not sedentary older adults — equally active ones. They added a third group of older adults who had trained seriously and consistently, defined as at least three structured hour-long sessions per week sustained for more than a year, and a fourth group of older adults with measurable physical impairment.
They took muscle biopsies before and after a bout of cycling and ran full multi-omic analysis: transcriptomics, metabolomics, and lipidomics. Because activity was matched between the young and the ordinarily active older adults, any molecular difference between those two groups could be attributed to aging itself rather than to inactivity.
Finding One: Muscle Aging Is an Energy Crisis
The dominant signature of aging muscle turned out to be metabolic. Compared with activity-matched young adults, older muscle showed reduced expression of the genes governing cellular respiration and energy metabolism — the machinery of the mitochondria, including subunits of ATP synthase, cytochrome c oxidase, and NADH dehydrogenase.
Mitochondria are the power plants of the cell, converting nutrients into ATP, the energy currency every muscle contraction spends. When the genes that build that machinery are downregulated, the tissue loses the capacity to generate energy efficiently. Alongside this, NAD⁺ — the coenzyme required for energy production and cellular repair — declined, and triglycerides accumulated inside the muscle: unburned fuel piling up in a tissue losing its ability to process it.
And critically: this happened in older adults who were walking as much as people in their twenties.
Finding Two: Training Erased About Half of It
In the older adults who had trained consistently for years, roughly fifty percent of the age-related molecular differences were absent. Their muscle profiles resembled those of young adults far more closely than their chronological age would predict.
And the changes training preserved were precisely the energy-metabolism ones. Mitochondrial respiratory genes that were depleted in the ordinarily active and impaired older adults sat at youthful levels in the trained group. The single most prominent feature of muscle aging turned out also to be the most preventable.
There is an important distinction buried here that deserves emphasis, because it is the part most people get wrong. Being generally active was not enough. The ordinarily active older adults matched the young adults on step count — and their energy metabolism genes declined anyway. What preserved the youthful molecular profile was structured, sustained training. Filling a step counter and being genuinely trained are not the same thing at the molecular level.
Finding Three: The Other Half Did Not Move
Here is the finding that matters most for anyone genuinely worried about frailty, and the one that rarely makes the headline.
About half of the molecular signature of muscle aging persisted in every older group — trained or not. These changes clustered in two areas: genes governing synaptic transmission, meaning the communication between nerve and muscle, and WNT signaling, a pathway central to tissue maintenance and stem cell function.
Read that again, because it reframes the entire conversation about strength and aging. The part of muscle aging that exercise cannot reach is not, primarily, about the muscle fibers themselves. It is about the nerves that drive them and the regenerative machinery that maintains them. Nature‘s own summary of the paper described these as the “unavoidable” alterations, in contrast to the “preventable” ones.
Unavoidable, that is, through behavior. That is exactly where therapeutics have to work — and where our own approach is aimed.
What Can Be Done About the Persistent Half
Put the two studies together and the case for acting is hard to ignore. Muscle is the tissue whose aging most strongly predicts death, and half of that aging does not yield to exercise. The persistent half is precisely where a therapy, rather than a training program, would need to work — and it has a definable shape: failing nerve-to-muscle communication and failing stem cell and tissue-maintenance signaling. That shape corresponds closely to what our therapies are designed to address.
We want to be careful in what follows. What we describe below is grounded in published mechanism and in what we observe clinically. No controlled trial has shown that these therapies reverse the specific gene changes the Nature Aging study identified, and none has shown that they extend lifespan or lower mortality — we make no such claim, and we would distrust anyone who did. What we can say is that the persistent, exercise-resistant half of muscle aging corresponds, mechanism for mechanism, to what these therapies are built to support.
Pluripotent Stem Cells and PSC-Derived Exosomes
The persistent half is characterized by declining synaptic transmission and impaired WNT signaling, which governs stem cell function and tissue maintenance. These are, in essence, failures of regeneration and of signaling — not failures of use.
This is the domain in which a pluripotent secretome operates. As we have described elsewhere in our work on exosome cargo, pluripotent stem cell-derived exosomes carry an unusually broad set of signals: neurotrophic factors supporting the nerve-to-muscle communication that this study found declining regardless of training; WNT-family members and BMPs directly relevant to the tissue-maintenance pathways implicated; the full sirtuin family and NAD⁺-synthesis components, which speak to the energy and NAD⁺ decline at the center of the aging signature; and mitochondrial-quality and antioxidant regulators. Pluripotent cells also natively carry signaling competent for neuroectodermal lineages — the origin of the nervous tissue whose communication with muscle deteriorates with age.
In other words: where exercise cannot reach, a regenerative signal may be able to. That is a hypothesis we take seriously and pursue carefully, and it is consistent with the improvements in muscle-related markers and functional capacity we observe in our patients.
Follistatin (FST-344): Releasing the Brake
Muscle mass is governed in part by myostatin, a protein whose entire biological job is to limit muscle growth. Follistatin is myostatin’s natural antagonist — the body’s own brake release.
Follistatin gene therapy raises circulating follistatin, and in preclinical work this is associated with increased lean mass, reduced fat accumulation, and improved metabolic profile. Where the Nature Aging study describes muscle losing its energetic capacity and accumulating intramuscular fat, follistatin addresses that same axis from a different direction: it favors lean tissue over fat and supports the maintenance of muscle mass itself.
It is worth being clear about what follistatin is and is not. It is not a substitute for training — it does not build the mitochondrial capacity that structured exercise builds. It is a systemic signal that shifts the body’s balance toward preserving muscle, which becomes more valuable precisely as the natural capacity to build and hold muscle declines.
LAV-BPIFB4: A Longevity Variant With Direct Frailty Evidence
Of all our therapies, LAV-BPIFB4 has the most direct published connection to frailty as such — not to muscle size, but to the clinical syndrome patients actually fear.
BPIFB4 is a secreted protein, and a particular haplotype of the gene — the longevity-associated variant, or LAV — was identified through genome-wide association studies as enriched in long-lived individuals across independent Italian, German, and American cohorts. In a study of 237 elderly subjects in Calabria, southern Italy, carrying the LAV haplotype in homozygosity was inversely correlated with frailty. Carriers of the opposite rare variant showed increased frailty and increased risk of death. In aging mice, systemic transfer of LAV-BPIFB4 delayed the progression of frailty.
There is a further connection that fits this study with unusual precision. Separate work has shown that LAV-BPIFB4 gene transfer rejuvenates the immune system and vasculature in part by reducing CD38⁺ macrophages and thereby limiting NAD⁺ decline. NAD⁺ depletion is one of the central findings of the Nature Aging muscle study. A therapy that acts on NAD⁺ availability through immune and vascular mechanisms is operating on the same deficit from a direction that exercise does not reach.
LAV-BPIFB4 also improves endothelial function and vascular health. Muscle is perfusion-dependent tissue; the capacity to deliver oxygen and nutrients is part of what determines whether it can maintain itself.
What This Means If You Are Afraid of Becoming Frail
Frailty is not a vague worry. It is the loss of the ability to carry your own groceries, to get out of a chair unaided, to recover from a fall or an illness that a younger body would shrug off. People are right to fear it — and the Nature Medicine finding gives that fear a hard evidential basis, because the aging of muscle predicts mortality more powerfully than the aging of any other tissue. Protecting muscle is not vanity. On the present evidence it is among the most consequential things a person can do for how long and how well they live.
What this study offers is an honest map, and the map has two territories.
- The preventable half is yours, and it is substantial. Structured training — not just steps, but sustained, planned, regular sessions — preserved roughly half the molecular signature of youthful muscle in people in their late sixties. That is an enormous return on a behavior available to almost everyone. No therapy we offer replaces it, and we would not want a patient to read this article and train less.
- The persistent half is a biological problem, and it needs a biological answer. Declining nerve-to-muscle communication and failing tissue-maintenance signaling do not respond to effort. This is where regenerative and longevity therapeutics have their rationale — not as an alternative to exercise, but as an answer to the part of aging that exercise has been shown, now with unusual clarity, not to touch.
The most sensible position, in our view, is to take both territories seriously. Train, because half of this is genuinely within your control and no injection substitutes for it. And address the other half deliberately, rather than assuming that effort alone will cover it — because this study is fairly clear that it will not.
The Encouraging Part
It would be easy to read a study like this as bad news: proof that aging comes for the disciplined as surely as for the sedentary. We read it the other way.
For most of medical history, frailty was simply what happened. There was no map of it, no division into what could be changed and what could not, and therefore nowhere for a therapy to aim. Now there is. We know that the energy crisis at the center of muscle aging is largely preventable through training. We know the residual half concentrates in neuromuscular signaling and tissue maintenance. Knowing precisely where behavior stops and biology begins is what makes it possible to do something about the second part rather than simply exhorting people to try harder at the first.
References
- Ding DY, Bot VA, Chen KL, Groves JW, Pálovics R, Masuda D, et al., Wyss-Coray T. Plasma proteomic signatures of cellular aging predict human disease. Nature Medicine. 2026. doi:10.1038/s41591-026-04446-y
- Janssens GE, Trętowicz MM, Grevendonk L, Kotte M, Scantlebery A, Schomakers BV, et al., Houtkooper RH. Delayed molecular aging, preservation of energy metabolism and enhanced exercise response in exercise-trained human muscle. Nature Aging. 2026;6:1482–1500. doi:10.1038/s43587-026-01150-x
- Villa F, Malovini A, Carrizzo A, Spinelli CC, Ferrario A, Maciag A, et al., Puca AA. Serum BPIFB4 levels classify health status in long-living individuals. Immunity & Ageing. 2015;12:27. See also: Puca AA, et al. LAV-BPIFB4 associates with reduced frailty in humans and its transfer prevents frailty progression in old mice. Aging (Albany NY). 2019;11(16):6555–6568. doi:10.18632/aging.102209
- Puca AA, Lopardo V, Montella F, Di Pietro P, Cesselli D, Rolle IG, et al. Transfer of the longevity-associated variant of BPIFB4 gene rejuvenates immune system and vasculature by a reduction of CD38⁺ macrophages and NAD⁺ decline. Cell Death & Disease. 2022;13:86. doi:10.1038/s41419-022-04535-z
