The Organ You're Slowly Losing

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Sarcopenia doesn't feel like anything in particular. That's the problem.

There's no pain, no obvious signal, no moment where something clearly goes wrong. Muscle mass simply begins declining — measurably, consistently, earlier than most people expect — and the body compensates well enough that the loss stays invisible for years. By the time it announces itself, it tends to do so indirectly. Stairs feel harder than they used to. A week of illness leaves a residue of weakness that doesn't quite go away. The body feels less available than it once was.

For most adults, this process begins in the mid-to-late thirties. Not at sixty. Not after retirement. Not following an injury that forced a period of inactivity. Now, or near enough to now that the distinction doesn't offer much comfort. At a rate of roughly one per cent per year from the forties, accelerating after fifty, sarcopenia is one of the most consequential and least discussed aspects of how the body changes with age — and it is the case for strength training for sarcopenia that this post is going to make.

It matters more than most people understand, and the reason is what muscle actually does.

The conventional understanding of muscle is mechanical. It contracts, moves bones, produces force. That is accurate but incomplete. Skeletal muscle is also the body's largest metabolic organ, responsible for the majority of insulin-stimulated glucose uptake and a key regulator of blood sugar, immune function, and systemic inflammation.

It also secretes signalling proteins during contraction that communicate with the brain, liver, bone, and fat tissue, suppressing inflammation and supporting neurogenesis in ways that don't occur when the muscle is simply present but underused. These functions are not passive. They require the mechanical stimulus of contraction to activate. They diminish not only as muscle is lost, but as the muscle that remains is used less.

Sarcopenia is the convergence of several mechanisms, each of which accelerates when not specifically countered.

The first is hormonal. Testosterone, growth hormone, and IGF-1 — the primary anabolic hormones — decline with age in both men and women. Oestrogen, which has a protective effect on muscle tissue, drops sharply through perimenopause and menopause. These changes reduce the rate at which the body synthesises muscle protein and shift the balance progressively toward net breakdown.

The second is neural. Motor units — the pairing of a motor neuron with the muscle fibres it controls — are lost with age, and the loss is not evenly distributed. Fast-twitch motor units, which govern power, speed, and rapid force production, are disproportionately affected. This is why the decline in explosive capacity tends to precede the decline in general strength. The ability to react quickly, catch a stumble, or generate sudden force diminishes earlier and faster than people expect.

The third is anabolic resistance. With age, muscle tissue becomes progressively less responsive to the signals that trigger protein synthesis — both dietary protein and the mechanical stimulus of exercise. The same training load and the same protein intake that maintain muscle mass at thirty produce a smaller response at fifty. The response doesn't disappear. It just needs a more deliberate and more consistent stimulus than it may have done earlier in life.

Sarcopenia rarely announces itself as sarcopenia. It presents as other things.

Fatigue that feels disproportionate to the activity. Recovery from illness or injury that takes longer than expected and leaves a residue of weakness that doesn't fully resolve. A metabolism that seems to have changed without obvious explanation. Joint discomfort that doesn't respond to treatment, because the muscular support around those joints has quietly diminished. A gradual narrowing of what feels easy — fewer stairs before breathlessness, heavier shopping, a reluctance toward activities that were once unremarkable.

None of these are inevitable features of ageing. They are features of muscle loss. Within meaningful limits, that is addressable.

The primary stimulus is resistance training — load applied to the muscle through a sufficient range of motion to produce a meaningful training response. It's worth being precise about what that means, because resistance training is not synonymous with weights.

The stimulus muscle responds to is mechanical tension: the experience of working against a load that challenges it. That load can come from a barbell, a cable machine, or a kettlebell. It can equally come from bodyweight movements that create sufficient demand on the relevant muscles. A well-progressed calisthenics program, a movement practice that includes loaded carries, pressing, and pulling patterns, or a combination of modalities will all do the job. What matters is not the implement. It is whether the muscle is being challenged sufficiently to generate a response, and whether that challenge increases progressively over time.

The 2019 consensus paper of the European Working Group on Sarcopenia in Older People (Cruz-Jentoft et al., Age and Ageing, 2019) identifies progressive resistance training as the central exercise intervention for both prevention and management of sarcopenia, with protein intake as the essential complement. Both are necessary. Neither alone is sufficient.

Protein provides the raw material for that response. Muscle protein synthesis requires amino acids — leucine in particular, which acts as a direct trigger for the synthesis process — and the quantity required increases as anabolic resistance develops. Recommendations vary. The major consensus papers — PROT-AGE and the ESPEN expert group — advise at least 1.0 to 1.2 grams of protein per kilogram of body weight per day for healthy older adults, rising to 1.2 to 1.5 grams for those with chronic illness or who are actively training to rebuild muscle. More recent sources influenced by the sports nutrition literature advise toward the higher end of this range, with some recommending over 2 grams per kilogram per day for those training seriously and seeking maximal muscle accrual. What the recommendations agree on: as the body becomes less efficient at using protein to build muscle, adequate intake becomes more important, not less. (Recommendations differ for adults with chronic kidney disease and certain other clinical conditions, and the optimal upper limit is still debated — speak to your GP if you're unsure where you sit.)

Power training — movements requiring rapid force production, such as jump variations, medicine ball throws, or explosive lifting — addresses the fast-twitch motor unit loss that standard resistance training doesn't fully target. This is not a consideration reserved for athletes. It is relevant to anyone who wants to maintain the capacity to react quickly, change direction, and recover balance when balance is disturbed. The capacity to catch a stumble before it becomes a fall is trainable. Most people don't think to train it until after the fall — which is also the conversation behind our Bone Defence class programming.

The honest answer is that the best time was a decade ago, and the second best time is now — regardless of where now finds you.

For those in their thirties and forties, the opportunity is preservation. Building and maintaining the muscle mass and neuromuscular patterns that will serve as a reserve against the accelerated loss of later decades. Muscle built now is easier to keep than muscle that has to be rebuilt. Patterns established now are more robust than those that need to be learned under the additional challenge of anabolic resistance and hormonal decline.

For those in their fifties and sixties, the opportunity is recovery and maintenance. Reversing some of what has already been lost while protecting what remains. The research is clear that meaningful adaptation — real, measurable increases in muscle mass, strength, and functional capacity — occurs at this age in response to the right stimulus. Anabolic resistance makes the process less efficient than it was at thirty. It does not make it futile. It makes adequate protein and sufficient training stimulus more important, not less.

For those further along, the evidence remains consistent. The canonical study here is Fiatarone and colleagues' 1990 trial in JAMA which demonstrated 174% average strength gains in institutionalised adults aged 90 and over after eight weeks of high-intensity progressive resistance training. The finding has been replicated and extended in the decades since — including a Cochrane review of progressive resistance training across 121 trials in older adults — and the underlying point holds. Skeletal muscle retains the capacity to adapt to progressive resistance training at every age. What changes is the margin — the difference between a body that has maintained muscle across decades and one that is starting the process later. That margin narrows with time, which is an argument for starting sooner, and an argument for continuing regardless of when you started.

The window doesn't close. It narrows. The work done inside it — at any point — produces outcomes that matter: stronger function, better metabolic health, greater resilience to illness and injury, and the physical capacity to remain independent in the ways that determine quality of life more than almost anything else.

Sarcopenia is quiet. The response to it doesn't have to be.

Infuse Health is a boutique movement and wellness studio at 4/10 William Street, Adamstown. You can start with a 4-week intro, a personal training session, or a single class — whatever fits what you're working with. Bookings through infusehealth.au.