Muscle mass after 40 — why it’s the one thing worth protecting

Most people in their forties don’t think about muscle. They think about weight. The scale is the number that gets watched, and as long as it isn’t climbing, everything feels roughly under control.

The problem is that the scale can’t tell you what you’re made of. Two people at the same weight, same height, same age can have completely different amounts of lean tissue — and completely different odds of being independent at eighty. Body weight is the least informative number in the room.

What actually happens to muscle as you age

Age-related muscle loss — clinically, sarcopenia — starts far earlier than most people expect. Research puts the decline at roughly 3–8% of muscle mass per decade after age 30, with the rate accelerating after 60.¹

It's quiet. Nobody wakes up at 45 and notices 6% less muscle. What they notice is that the stairs feel longer, that a heavy suitcase is a two-hand job now, that getting off the floor involves a plan. Those aren't separate problems. They're the same problem, showing up late.

And because muscle is metabolically expensive tissue, losing it quietly lowers the amount of energy you burn at rest. Which is why people often find weight creeping up in their forties despite eating roughly what they always have. The maths changed underneath them.

Muscle isn’t just for moving things

The strongest case for training after 40 isn’t aesthetic. It’s that skeletal muscle does several jobs that only become obvious once it’s gone.

It’s where your body puts glucose

Skeletal muscle is the largest site of glucose disposal in the body. More lean tissue means more capacity to handle carbohydrate without it sitting in the bloodstream. Less muscle means the same meal lands harder.

It loads your skeleton

Bone responds to being loaded, and the main thing that loads it is muscle pulling on it. Progressive resistance training is one of the few interventions shown to slow — and in some cases reverse — age-related bone mineral density loss, which matters most around and after menopause when decline accelerates sharply.^2,3

It’s the difference between a stumble and a fall

Catching yourself when you trip is a power quality — the ability to produce force quickly. Power declines faster with age than strength does. A fall at 75 that ends in a fractured hip is very often the beginning of a much worse story, and the ability to avoid it was built decades earlier.

This is what we mean when we talk about longevity training rather than fitness. The goal isn’t a number on a lift. It’s that you’re still carrying your own shopping, playing with grandchildren on the floor, and getting up from it unassisted, thirty years from now.

Why cardio isn’t enough

Walking is genuinely good for you. So is swimming, so is cycling. They do real things for cardiovascular and metabolic health, and most people should do more of them.

But none of them meaningfully protects muscle. They aren’t progressive — you can walk the same 5km for twenty years and the stimulus never increases — and they don’t load tissue heavily enough to signal that it’s worth keeping. Someone who walks daily and does nothing else will still lose muscle on schedule.

Australia’s physical activity guidelines separate the two for exactly this reason: 2.5–5 hours of moderate activity per week, plus muscle-strengthening activities on at least two days.⁴ The second half is the part that gets skipped. Only around 4 in 10 Australian adults aged 18–64 meet it.⁵

That gap is usually not about motivation. It's about not knowing what to do once you're in front of a rack, and not wanting to find out in front of an audience.

What protecting it actually looks like

The good news is that muscle responds at any age. Studies in adults well into their seventies and eighties show meaningful gains in strength and lean mass from progressive resistance training. The tissue hasn’t stopped listening — it just stopped being asked.

That last one is the reason we cap our semi-private sessions at three people per coach. Progressive loading only works if someone is watching the movement it's being applied to. Past three, that stops being true, and you're just a person lifting weights near a trainer.

Starting at 45, 55 or 65

The most common thing we hear at a first consultation is some version of “I’ve left it too long.”

You haven’t. What changes with age isn’t whether training works — it’s how much precision it requires. Joint load has to be managed rather than ignored. Structural imbalances that were invisible at 25 need addressing before they’re loaded. Recovery takes longer, so programming has to account for it rather than assume you’ll bounce back.

None of that is a reason not to start. It’s a reason not to start alone, guessing, from a program written for someone else.