How to Maintain Muscle After 40: What Actually Works

There's a slow, steady decline that adds up over decades. And there's a faster, sharper kind of loss from illness and immobility — the part that's underappreciated, even within healthcare.

Both share a common cause. Your body is constantly adjusting to what it thinks you need. If you use your muscles less — whether through years of gradually doing less, or a few weeks of being too sick to move — your body assumes you don't need them and quietly takes them away.

Let's look at each.

The slow drift

From your forties onwards, you start losing about one percent of your muscle each year. The rate accelerates after 60.

Several things drive it. As estrogen falls in women and testosterone gradually declines in men, the body's signals to maintain muscle weaken. Your muscles also become less responsive to protein — they need a bigger dose to trigger the same growth response, a phenomenon called anabolic resistance. And life simply changes. You sit more. Your sport drops away. Your protein intake quietly drifts down. The signals telling your body to keep muscle get fainter, and the body responds by letting some go.

Strength fades faster than muscle mass — and power, which is strength used quickly, fades faster still. So the muscle in your thigh might still look fine, but standing up from a chair feels harder than it used to. That's not your imagination. The mass is largely there. The strength to use it is going first.

The sharp losses

Here's something that's less well known, even within healthcare.

Your muscle is in constant turnover. Every day, about one to two percent of the protein in your muscles is broken down and rebuilt. Within two or three months, much of your muscle is essentially new tissue.

This is what makes muscle so adaptable. It's why training works at any age, why injuries heal, and why someone in their 80s can still build new muscle.

But the same fast turnover that lets muscle adapt also makes it vulnerable when something goes wrong. When you stop using your muscles — even for a few days — your body decides you don't need them and breaks them down quickly.

The numbers are striking:

• Two days of bed rest — measurable muscle loss begins.
• Seven days of bed rest — about five percent muscle loss.
• Ten days of bed rest in older adults — around a kilogram of leg muscle gone, alongside a sixteen percent drop in leg strength.
• Ten days in intensive care — losing around eighteen percent of one of your major thigh muscles. The inflammation of serious illness compounds the disuse, and muscle dissolves at a rate that matches decades of normal aging.

Now here's the part that really matters. Without active rehabilitation, you don't get all of it back. A young adult immobilised for two weeks can return to baseline with two weeks of normal retraining. An older adult often won't — not because their body can't recover, but because the structured rehabilitation needed to drive that recovery rarely happens. They get most of it back, but not all. Each illness episode leaves a small permanent loss.

So a sedentary 70-year-old struggling to get up from a chair isn't simply experiencing aging. Some of it is. But a large part is twenty years of slow drift plus three or four illness episodes — none of them properly rehabilitated — quietly stacked on top of one another.

This is the part healthcare systems still don't fully appreciate. Strength is rarely measured before, during, or after a hospital stay. Protein intake during admission is dramatically lower than what's recommended — research across the UK, Netherlands, Italy, Denmark, and Australia consistently finds older patients consuming around 0.65 grams of protein per kilogram per day, less than half what's needed during recovery. Hospital food often isn't appealing, patients aren't hungry, and nobody intervenes.

The good news is there's a lot you can do about both halves of this picture — the slow drift and the sharp losses. That's what the rest of this article is about.