Anabolic resistance — the body’s blunted ability to build and maintain muscle as we age — is one of the most clinically underappreciated shifts in physiology. Understanding it changes how we support our patients.
There are moments in medicine where the conversation starts to shift, and right now, I see that happening around muscle.
Not muscle in the aesthetic sense — not the gym culture version — but muscle as a metabolic organ. As a longevity tissue. As something that quietly governs insulin sensitivity, inflammatory signalling, immune resilience, and the basic physical capacity to remain functional and independent into later decades. The science here has been building steadily, and it’s reaching a point where it’s hard to look at aging patients without putting muscle near the top of the clinical picture.
And yet, even as muscle takes center stage in the longevity conversation, there are still gaps in how we’re thinking about it. One of them surfaces regularly in practice: patients who are eating enough protein, exercising consistently, sleeping reasonably well — and still not building or maintaining the muscle mass we’d expect. The numbers don’t add up. The effort is there. The results aren’t.
More often than not, anabolic resistance is somewhere in that gap. It’s a concept that deserves more space in clinical conversations than it currently gets — and it offers a meaningful lens for understanding not just muscle loss, but how aging, inflammation, protein metabolism, and lifestyle inputs intersect in ways that aren’t always visible on a standard panel.
What anabolic resistance actually is
In a healthy, younger physiology, muscle protein synthesis (MPS) responds robustly to two main stimuli: dietary protein and mechanical load from exercise. Eat a protein-containing meal, and MPS rises. Perform resistance exercise, and MPS rises again — and the two stimuli together produce a synergistic effect. This is the engine of muscle maintenance and growth.
Anabolic resistance describes a state where that engine has become less responsive. The stimuli are present — protein is consumed, exercise is performed — but the downstream signalling cascade that translates those inputs into new muscle tissue is blunted. The threshold for triggering a meaningful MPS response rises. The magnitude of that response, once triggered, diminishes. Recovery from exercise-induced muscle damage slows. The net result, over time, is that older adults require more of the inputs that younger adults need less of, and even with those higher inputs, the yield is lower.
Anabolic resistance isn’t a failure of effort or discipline. It’s a shift in the body’s sensitivity to signals it used to respond to reliably — and recognising that changes what we ask of our patients.
This isn’t a fringe phenomenon. Studies consistently show that adults over 65 demonstrate a significantly attenuated MPS response to equivalent protein doses compared with younger adults. The mechanisms are multiple and interacting: reduced mTORC1 signalling activity, elevated basal inflammation (often called inflammaging), impaired amino acid sensing in muscle tissue, anabolic hormone decline — particularly testosterone and IGF-1 — and mitochondrial dysfunction that limits the energy available for protein synthesis.
The role of inflammation
Chronic low-grade inflammation is one of the most consistent features of aging, and it intersects with anabolic resistance in direct, mechanistic ways. Elevated circulating cytokines — TNF-α, IL-6, IL-1β — activate catabolic pathways in muscle tissue while simultaneously suppressing the anabolic signalling that drives MPS. This creates a state where muscle is being broken down faster than it’s being rebuilt, even in the absence of acute illness or injury.
What makes this clinically relevant is that the inflammatory state driving anabolic resistance is often invisible on standard labs. A patient with a normal CRP can still carry a meaningful inflammatory burden — particularly if it’s tissue-level or driven by metabolic dysfunction, gut permeability, or adipose-derived signalling. The framing of “normal” labs as reassurance has its limits here.
Inflammaging and muscle
The term “inflammaging” captures the low-grade, chronic, sterile inflammation characteristic of biological aging. In muscle tissue, this environment suppresses the mTORC1 pathway — the primary hub of muscle protein synthesis signalling — and upregulates ubiquitin-proteasome activity, accelerating protein breakdown. It’s a dual insult: less building, more breaking down.
Protein quantity alone is not the answer
The standard recommendation for older adults — eat more protein — is correct but incomplete. Yes, the protein intake threshold for stimulating MPS rises with age. Where 20–25g of high-quality protein may be sufficient to maximally stimulate MPS in a younger adult, older adults often require 35–40g per meal to achieve a comparable response. Spreading protein more evenly across meals, rather than concentrating it at dinner, matters more than most patients realise.
But quantity and distribution don’t fully address the sensitivity problem. The anabolic resistance that drives blunted MPS isn’t only about getting enough leucine to the muscle — it’s about whether the muscle can actually respond to it. That’s where the conversation needs to go further.
Leucine, specifically, is worth understanding. As the primary trigger of mTORC1 activation in muscle, it acts more like a signalling molecule than a structural building block. In the context of anabolic resistance, higher leucine thresholds are needed to trip the same signalling cascade. This is one reason why leucine-enriched protein supplements — or protein sources naturally high in leucine, like whey and animal proteins — tend to outperform plant-based proteins of equivalent gram weight in studies of older adults, unless the plant protein dose is meaningfully higher.
Protein per meal, older adults
35–40g Needed to match the MPS response a younger adult achieves with 20–25g
Sarcopenia prevalence
~10% Of adults over 60 globally — rising sharply with age; often underdiagnosed
Muscle loss rate
3–8% Per decade after 30 — accelerating after 60 without targeted intervention
What actually moves the needle
Addressing anabolic resistance requires working on multiple levers simultaneously — no single intervention is sufficient on its own. The most evidence-supported approach combines targeted nutrition, specific exercise modalities, inflammation management, and attention to hormonal context.
On the exercise side, resistance training remains the most potent stimulus for MPS regardless of age, and its benefits in anabolic resistance are dose-dependent. Higher-load, progressive resistance training consistently outperforms lower-load protocols in restoring anabolic sensitivity in older adults. The evidence also supports combining resistance training with brief high-intensity intervals as a way of amplifying mitochondrial adaptations that support the energetics of muscle protein synthesis.
Timing matters more than it used to, practically speaking. Consuming protein — ideally 35–40g of high-quality, leucine-rich protein — within the post-exercise window (30–60 minutes) appears to partially overcome the blunted post-exercise MPS response seen in anabolic resistance. It doesn’t eliminate it, but it helps. For patients resistant to this idea, the framing I find useful is this: the exercise opens a window that’s already narrower with age; what you eat before it closes determines what you get from it.
Creatine monohydrate deserves mention here more prominently than it typically receives in clinical conversations. A substantial body of research supports its role in augmenting MPS response to resistance training in older adults, supporting phosphocreatine resynthesis, and improving muscle function independent of changes in lean mass. It’s inexpensive, well-tolerated, and the evidence base is unusually strong for a supplement. In the context of anabolic resistance specifically, it appears to lower the effective threshold for anabolic signalling — which is precisely where the problem lies.
The exercise opens a window that’s already narrower with age. What you eat before it closes determines what you get from it.
Omega-3 fatty acids — EPA and DHA specifically — have demonstrated a direct sensitising effect on muscle anabolic signalling. Multiple randomised controlled trials have shown that omega-3 supplementation in older adults augments the MPS response to amino acid infusion and to resistance exercise, without changing the protein or exercise dose. The mechanism appears to involve incorporation of EPA and DHA into muscle cell membranes, enhancing the fluidity and receptor function needed for insulin and mTOR signalling. This is a case where the nutritional intervention isn’t working around the problem — it’s working on the mechanism directly.
Vitamin D status is consistently associated with muscle function and anabolic signalling, though the intervention trials in repletion alone are mixed. What seems clearer is that deficiency creates a permissive environment for anabolic resistance, and that maintaining adequate levels — rather than treating deficiency after the fact — is the more useful clinical target.
The hormonal context we can’t ignore
Anabolic resistance doesn’t exist in a hormonal vacuum. The decline in testosterone, estrogen, IGF-1, and growth hormone that accompanies aging contributes directly to the signalling environment inside muscle tissue. Testosterone and IGF-1 are upstream activators of the mTORC1 pathway; their decline reduces the anabolic tone of muscle even before any protein or exercise stimulus is applied.
This is where the conversation connects to hormonal support — not as a standalone intervention, but as part of the broader picture of restoring the conditions under which muscle can respond normally to the inputs we’re providing. For patients already navigating perimenopause or hypogonadism, the anabolic resistance conversation is inseparable from the hormonal one. Treating them separately, in clinical silos, misses the interaction.
What this means in practice
The patients I think of when I consider anabolic resistance are not sedentary. They’re often the ones who are engaged — tracking protein, training consistently, taking their supplements. What’s frustrating for them, and for us, is that the standard feedback loops don’t apply. More effort doesn’t produce proportionate returns. That disconnect is worth naming explicitly, because it changes the therapeutic conversation from “are you doing enough?” to “what is your body’s current capacity to respond, and how do we work with that?”
Clinically, this means looking more carefully at inflammation markers beyond standard CRP, assessing hormonal context, reviewing protein distribution rather than just daily totals, considering creatine and omega-3 as primary rather than optional interventions, and matching exercise modality to what the evidence actually supports for this specific problem.
It also means having a more honest conversation with patients about timelines. Reversing anabolic resistance is possible — there is good evidence that the signalling sensitivity can be partially restored, particularly with consistent resistance training, targeted nutrition, and inflammation reduction. But it takes longer than building muscle in a younger physiology. Expectations calibrated to that reality serve everyone better.
As always, I hope this gives you something useful to bring into your work — and perhaps a new lens on how you’re thinking about aging, resilience, and long-term muscle health.
Key sources
Burd NA et al. “Anabolic resistance of muscle protein synthesis with aging.” Exercise and Sport Sciences Reviews, 2013.
Moore DR et al. “Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men.” Journals of Gerontology, 2015.
Smith GI et al. “Omega-3 polyunsaturated fatty acids augment the muscle protein anabolic response to hyperinsulinaemia–hyperaminoacidaemia in healthy young and middle-aged men and women.” Clinical Science, 2011.
Landi F et al. “Sarcopenia as the biological substrate of physical frailty.” Clinics in Geriatric Medicine, 2015.
Candow DG et al. “Creatine supplementation for older adults: focus on sarcopenia, osteoporosis, frailty and Cachexia.” Bone, 2022.
Franceschi C et al. “Inflammaging: a new immune-metabolic viewpoint for age-related diseases.” Nature Reviews Endocrinology, 2018.
Morton RW et al. “A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength.” British Journal of Sports Medicine, 2018.
This post is for educational purposes and does not constitute medical advice. All clinical decisions should be made in collaboration with a qualified healthcare provider.