What is sarcopenia, and when does muscle loss actually start?

The age-related loss of muscle mass, strength and function — and the important correction is that meaningful decline starts far earlier than most people assume, and that strength is lost faster than mass.

The timeline. Muscle mass typically peaks in the twenties to thirties and begins a slow decline from around the fourth decade, accelerating after 60 and again after 75. Typical figures are on the order of 3–8% of mass lost per decade after 30, with the rate roughly doubling after 60.

Strength declines faster than size, and power — force produced quickly — declines faster still. This matters because power, not mass, is what determines whether someone can recover from a stumble or rise from a chair, which is why function can deteriorate while weight stays constant.

What drives it:

Loss of motor units, particularly those serving fast-twitch fibres, as motor neurons die and are incompletely replaced.

Anabolic resistance — older muscle responds less strongly to a given dose of protein, so the same intake produces less building.

Reduced physical activity, which is both a cause and a consequence.

Chronic low-grade inflammation and hormonal changes.

Periods of bed rest or immobility, which cause disproportionate loss in older adults and from which recovery is slow and often incomplete. A single hospital admission can be a step change, which is why early mobilisation matters so much.

Why it matters clinically. Sarcopenia predicts falls, fractures, loss of independence, longer hospital stays and mortality. Sarcopenic obesity — low muscle with high fat mass — is particularly associated with poor outcomes and is easily missed, because body weight looks unremarkable.

What actually works:

Progressive resistance training, which has by far the strongest evidence and works into very advanced age — gains have been demonstrated in people in their nineties.

Power-oriented work — moving lighter loads quickly — specifically targets what declines fastest.

Adequate protein, typically higher than general adult guidance and distributed across meals to overcome anabolic resistance.

Starting earlier, since peak mass sets the baseline you decline from.

General information, not medical advice.