Why muscle, not weight, is the number that matters after 60

Somewhere in your thirties, without any announcement, your body begins quietly shedding muscle. The usual estimate is three to eight per cent of muscle mass per decade from around age thirty, and the rate roughly doubles after sixty. For most people this happens silently, because bodyweight often stays flat or even creeps upward — fat moves in as muscle moves out, and the scale reports nothing unusual.

This is the central problem with weight as a health metric in later life. It measures the wrong thing. A seventy-year-old who has lost six kilograms of lean tissue and gained six kilograms of fat has had a genuinely bad decade, and the scale will show a perfectly stable number the entire time.

What sarcopenia actually costs you

The clinical name for age-related muscle loss is sarcopenia, and it is not simply a cosmetic matter of looking softer in a shirt. Muscle is the tissue that gets you off a low sofa, catches you when a kerb comes up faster than you expected, and carries a suitcase up a flight of stairs at an unfamiliar station. It is also metabolically active — it is where most of the glucose you eat gets taken out of circulation, which is part of why muscle loss and insulin resistance tend to arrive together.

The European Working Group on Sarcopenia in Older People revised its definition in 2019 to lead with muscle strength rather than muscle size, which tells you something important. Two people can carry the same amount of lean tissue and have very different capacity, because the nervous system's ability to recruit that tissue also declines. Strength falls faster than mass does. That is bad news in the sense that the problem is bigger than it looks, and good news in the sense that strength responds to training faster than mass does.

The downstream consequences are well documented. Low muscle strength predicts falls, fractures, longer hospital stays, slower recovery from surgery, loss of independence and mortality — and it does so fairly consistently across large cohort studies. Grip strength alone, measured with a cheap hand dynamometer, turns out to be one of the more useful single predictors in geriatric medicine, which is faintly absurd but repeatedly confirmed.

The unwelcome part: it has to be resistance training

Walking is genuinely good for you. It is good for your heart, your mood, your blood pressure and your sleep. What it will not do is meaningfully rebuild lost muscle, because the load is too low and never increases. If your only exercise is walking, you can be quite fit and still be losing the tissue that determines whether you can get up off the floor.

The stimulus that reverses sarcopenia is resistance training — loading the muscle against something heavy enough that the last few repetitions are genuinely difficult. The evidence here is unusually strong and unusually old. Maria Fiatarone's much-cited 1994 trial put frail nursing-home residents, average age eighty-seven, through ten weeks of progressive resistance training, and they gained strength and walking speed. The oldest participant was ninety-eight. The idea that it is ever too late to start has been dead in the literature for thirty years; it just has not filtered through to the general public.

Two sessions a week is the usual recommendation and it is enough. Six to eight exercises covering the legs, the hips, the push, the pull and the trunk. Two or three sets each, stopping two or three repetitions short of failure. The load matters more than the machine — resistance bands, dumbbells, gym equipment and bodyweight all work, provided the effort is real and it goes up over time.

Protein, and why the standard advice is too low

Older muscle is less responsive to protein than young muscle, a phenomenon usually called anabolic resistance. The practical consequence is that the recommended dietary allowance of 0.8 g per kilogram of bodyweight — which was derived largely from studies in younger adults, and is a floor for preventing deficiency rather than a target for thriving — is probably inadequate after sixty.

The PROT-AGE study group and several subsequent consensus papers suggest 1.0 to 1.2 g/kg for healthy older adults, and up to 1.5 g/kg for those who are ill or recovering. For a seventy-kilogram person that is roughly 70 to 85 grams a day, spread across meals rather than piled into dinner, since there appears to be a per-meal threshold of around 25 to 30 grams needed to trigger muscle protein synthesis in older adults.

One caveat that matters: if you have reduced kidney function, higher protein intakes need to be discussed with your doctor rather than adopted from an article. This is one of the genuinely individual questions.

What to do with this

Stop weighing yourself daily and start measuring what you can do. How long the chair-stand test takes. Whether you can carry the shopping in one trip. How many stairs you manage before you need the handrail. These are the numbers that track the thing you actually care about, which is not a figure on a scale but the size of the life you can still reach.

Then train for them, twice a week, with something heavy enough to be inconvenient. The tissue is more willing to come back than most people expect.