Why Aging Muscles Shrink — And How to Stop It

Ready for a mind bender? Let's start with a basic assumption almost everyone has about muscles and aging. The older you get, the more muscle you lose. And that's not just aesthetic. Muscle is tied to your mobility, it's the foundation of your metabolic health, it is your very independence. It's the difference between freedom as we age and friction, where everything in life is just harder. So the advice is always the same: build muscle To keep it, lift weights, eat protein. Kinda bland, right? But there's a paradox hidden inside the biology of your muscle. Basically, a signal in your muscle telling it to build. And if muscle is wasting away with age, you'd expect that signal to be fading, right? But a new study suggests the opposite. In aging muscle, the build and grow signal is actually higher! So what gives? Why is muscle tissue still shrinking as we age? As a metabolism scientist, I was scratching my chin when I read this thinking, "Wait, this doesn't make sense," until it clicked. And that's the problem we're gonna unravel together today. And I'm not only gonna give you a peek inside the fascinating biology of muscle, but I'll also give you actionable insights to help build muscle today and keep your muscle for decades to come. Let's get into it. Muscle isn't optional, it's foundational. Exercise does two things: It signals muscles to grow and the aging muscle paradox. Cumulation of molecular junk are slamming the muscle growth button. Wait, this doesn't make sense. It does more than promote growth. It has a dark side. Okay, first a roadmap to this video. In Chapter 1, we're going to talk about the aging muscle paradox. I'll walk you through these new findings, what makes them paradoxical, and ultimately why they do make sense. Then in Chapter 2, we're going to talk about how exercise makes your muscles young while also building them up. In Chapter 3, we're going to zoom back and broaden the scope of our discussion and review why muscles are much more than what we think. Then in Chapter 4, we're going to talk about specific high-yield strategies to support muscle health with aging. And as always, if you want the references, extra nuance, and early access to this type of deep-dive content, check out the Stay Curious Metabolism newsletter and join the growing community of people like you who aren't satisfied with the keep it simple stupid explanations, but who want to grapple with the nuance and complexity. So with that, I got myself fired up, but warmup over, let's get into Chapter 1: The Aging Muscle Paradox. The paper in question that delivered that "wait, this doesn't make sense" moment for me was published in the Proceedings of the National Academy of Sciences. But to understand the paradox presented in the study, you first need to know about mTOR. mTOR is a protein complex found in muscle and throughout the body that positively regulates growth pathways. A simple way to think about it is it's basically the big red go button for growth. And it's critically important for building muscle, as I mentioned. So here's a simple thought question: what do you think happens to mTOR activity in muscle as people age and lose muscle? If you're applying basic reasoning, you probably think mTOR activity declines with age, contributing to muscle loss, right? It's the go button for muscle growth, So if you're losing muscle, it must go down. That would be a reasonable guess, that would have been my guess, but it's wrong. In aging muscle, and especially in sarcopenia, which is age-related muscle wasting, mTOR activity is actually higher, not lower. That's shown in this paper. The researchers examined mTOR expression in aging muscle compared to younger adults. Older adults showed higher mTOR expression. It's kind of odd. Therefore, older muscles are slamming the muscle growth button, the mTOR button, but they're simultaneously wasting away. That's the paradox. That's the moment of, "Wait, this doesn't make sense." Now, I want to encourage you to pause and grapple with this problem in your own mind. How would you resolve the paradox? Do you have a thought? Do you have a hypothesis? Well, my My first hypothesis myself was something like hormone resistance, right? Maybe the signal is there, but the muscle can't respond to it. Kind of like insulin resistance— insulin levels can be high, but not all tissues are getting the insulin signal. But that's not the case either. The reality, the problem, turns out to be much more interesting. That's because, and this is a key detail you need to know, mTOR does more than promote growth. It has a dark side. It also suppresses cellular recycling and renewal pathways, especially one you might have heard of called autophagy. Autophagy. Autophagy is how cells clear out damaged proteins and dysfunctional components. So what happens is chronically elevated mTOR stalls the cleanup process, and the result is an accumulation of molecular junk, dysfunctional proteins, and increases in biomarkers of cell aging, so-called cellular senescence. So, simply put, mTOR is a double-edged sword. It does promote growth, but it also blocks renewal. And this nuance, this critical nuance, helps explain why aging muscle can show chronic mTOR overactivation and it makes sense. The growth signal is high, but quality is deteriorating, so over time the accumulation of the molecular damage from suppression of autophagy and renewal processes overpowers the growth and muscles waste away. So we already know mTOR is overactive in aging human muscle and this correlates with muscle loss. But can we, in theory, solve the problem of mTOR overactivation? Can we quiet this pathway, and if we do, can we restore healthy muscle function with age? Now, to answer this question, we do need animal experiments, and in this case, fruit flies, also known as Drosophila. And I know fly data doesn't necessarily excite everyone, and if I'm being dead honest with you, I honestly have a little bit of PTSD— P.T.S. Drosophila— from the millions of flies I sorted during my time in a fly lab as an undergraduate at Dartmouth. But let's set that aside, because these pathways are highly conserved, from flies to mice to humans. So this allows for an incredibly clean experiment. And as flies age, a proxy for their muscle function is climbing ability, how fast they can climb up a side of a container. And what you see here is climbing ability muscle function declines sharply with age, the green and blue. But when researchers silence the mTOR pathway, which they did by blocking something upstream of mTOR, called DEF1, muscle function was preserved well into old age, which in fly terms is only 6 weeks, because fly life is kinda tough. But to be clear, if mTOR is the big red grow button, DEF1 is the finger pressing it, so for our purposes they kind of go together—more DEF1 activity, more mTOR, and vice versa. And muscle structure told the same story. If you look at these young muscles, they show dense organized filaments, actin filaments. Old muscles show degeneration, all this black space. But if you suppress the DEF1-mTOR cycling pathway, older muscles start to look young again. And we see similar patterns for autophagy, the cellular recycling, and markers of cell aging, the senescence. Basically, when the DEF1-mTOR pathway is tuned down, muscles look and act and function younger. So as a quick summary so far: in aging, DEF1 and mTOR are elevated. This impairs cellular recycling, leads to an accumulation of molecular junk, and drives muscle deterioration. But when DEF1 mTOR signaling is suppressed, basically when the finger is lifted off the mTOR button, muscle quality improves, renewal resumes, and aging slows. That brings us to Chapter 2: How exercise makes muscles young while also growing them. You see, exercise has a beautifully complex relationship with mTOR. In the short term, like right after a workout, it causes a spike in mTOR activity, exactly what you want to stimulate muscle growth. But over the longer term, chronically, exercise suppresses basal levels of DEF1 mTOR overactivation. So in effect, exercise does two things: it signals muscles to grow, and it restores efficient recycling and renewal processes. Growth and cleanup—it's the best of both worlds. It's kind of like if I could make dinner for my girlfriend and leave a sparkling clean kitchen, except this latter scenario is total fantasy and the mTOR muscle thing is real. But moving on, if you want some more evidence, in older mice, both endurance exercise and resistance exercise reduced mTOR levels compared to sedentary control mice. Also, exercise increased autophagy, reduced cellular senescence. So in short, exercise literally rejuvenates muscles at the deep molecular layer. Now, let's pause and zoom out, and bring us to Chapter 3: Muscles Aren't What You Think. They're much more. I really want to make a global point in this little chapter. We often think of muscles as purely mechanical—the bigger they get, the heavier we can lift. Simple. But an underappreciated fact—and this is a fact—about muscles is they are endocrine organs. In fact, they make up the largest endocrine organ in the body, secreting hormones just like the thyroid or adrenal glands. Muscles are total factories for hormones, and also non-hormonal messengers like small extracellular vesicles, These vesicles carry microscopic cargo that tell other organs how to express genes and make proteins. And this sort of inter-organ communication, between-organ communications—think muscle to heart, muscle to brain, muscle to fat tissue—determines how our hearts can handle a heart attack—you can see this video for more—or even how our minds develop or don't develop depression or mental health. Muscle is an endocrine organ that determines so much of our physiology and even mental well-being. There are even strong associations between lean muscle And last, in higher levels of NAD+, a key energy-carrying molecule that is linked to cognitive resilience and can play roles in Alzheimer's prevention. You can see this for more. The bottom line: muscles are not just mechanical; they're nodes in a vast signaling network that helps regulate our overall health, from liver to heart to brain and beyond. And that brings us to Chapter 4: High-yield, specific strategies to support healthy muscle aging. Now, first and foremost, the most important factor in healthy muscle aging is resistance training. It is absolutely essential. Trying to stack supplements on top of a sedentary lifestyle, it's kind of like throwing gummy multivitamins at an ice cream sundae. It misses the point. But I suspect you know that, and you probably know that protein is also critical for healthy muscle, so let's get a little bit deeper into some more outside-the-box ideas that can help support healthy muscle aging. First up, creatine. Creatine is the most well-studied nutraceutical out there, or at least one of them, and it's not just for bodybuilders. It's for everyone who wants to have healthy muscle aging. Because as we age, our muscles need more support, and creatine meets that demand. There is a vast amount of data showing it can increase muscle power, promote hypertrophy muscle growth, and may even support fat loss. How creatine works is fascinating. It does several things. For example, it pulls water into muscles, which is a growth stimulus. It activates muscle stem cells called satellite cells, and it increases the expression of long filamentous proteins needed to build muscle fibers. Personally, I think it makes sense to start at 5 grams of creatine monohydrate daily as a protocol, ideally consumed with food to reduce the chances of bloating and gastrointestinal upset. I do a deep dive on creatine in this video, and if you want to use the creatine I use, it's Momentous Creatine Monohydrate. I do choose this product specifically because of its rigorous third-party testing. It's extensively tested for things like heavy metals and banned substances. While there are options for gummies and flavors, my personal preference is their pure unflavored, no dyes, no sweeteners, micronized creatine monohydrate. I think it's very clean, efficient. I like to mix it into my Greek yogurt, or if I'm feeling indulgent, I sometimes make a creatine ice cream. I also love making creatine ice cream, and I'll, uh, drop the recipe below. Anyway, if you want to try this creatine, you can use my discount code STAYCURIOUS for up to 35% off your first order at livemomentous.com. Again, check the link below. But in a phrase and summing up on creatine, it's not just about lifting heavier for ego, it's about preserving strength for life. Now, next up on our list, something a bit more esoteric, maybe you haven't heard of: sarcosine. Sarcosine is an unusual amino acid, protein building blocks, and in recent studies it's been shown to help counter age-related muscle loss. In both humans and animals, sarcosine levels tend to decline with age and in sarcopenia, but in preclinical trials, sarcosine supplementation effectively prevents age-related muscle loss. Now, to caveat, the research is still very early on sarcosine, but it's a pretty safe supplement, and if you want to try it, the human equivalent dosing drawn from the preclinical literature is only about half a gram per day. If you want more on it, see this video, in which I also do push-ups with my mom. But moving on, omega-3s. Long-chain omega-3 fatty acids provide a wide range of benefits, including positive effect on muscle. They promote muscle health by reducing inflammation, improving insulin sensitivity, and enhancing muscle protein synthesis. For dosing, the literature generally supports 1.5 to 2 grams per day for overall health. And you can get this just from seafood alone. Think sockeye and sardines. You can supplement if you want, but you can just get it from seafood alone. And finally, another oddball on our list, oleuropein. This is a natural compound found in olives and olive leaves, and it shows a promising link between energy metabolism and muscle cell activity. Basically, oleuropein naturally activates something called the mitochondrial calcium uniporter, which gets calcium into mitochondria, which is needed to unlock energy production. This tends to decline with age, and in animal studies, oleuropein has been shown to improve muscle performance and even increase muscle mass. It's most readily available in olive leaf extract, as I mentioned, and typically dosed between 500 and 1,000 milligrams per day, so half to 1 gram. I do a deep dive on oleuropein in this video, and it's kind of a throwback so you can see how far my editing process has come. Anyway, in the end, let's wrap up. Muscle aging? Isn't just about shrinking biceps. It's a window into the deeper mechanics of how our bodies age. From the paradox of aging muscle and mTOR that we discussed in this video, to the elegant rejuvenating effects of exercise on muscle, we're learning that muscle is about much more than just lifting heavier. That's the truth, or truths. Muscles aren't just contractile utensils, but complex signaling powerhouses, dynamic, calibrated in incredible ways we're only beginning to understand, and in constant conversation with the rest of our body. Mussels literally shape how you think, how you age, and how resilient you are to disease. So what we need to do now with this knowledge, what do we do? We train, we move, we nourish with intention. Bottom line, if you want to keep your body younger for longer, muscle isn't optional. It's foundational. And cutting through all the complexity, there is one simple fact. The best time to start building better muscle is always the same. Right now.