Why You Start Losing Muscle at 40, and the Science of Getting It Back

Key Takeaways

• Muscle mass declines by roughly 3% to 8% a decade from around age 30, with the loss often becoming noticeable in your 40s and quickening in the 60s and 70s.
• The loss reflects fewer and smaller muscle fibres, falling anabolic hormones, weaker nerve signals, a blunted response to protein and rising inflammation.
• Resistance training with enough protein can slow the decline and help regain some strength and function at almost any age.
• Weak muscles add strain to the knees and hips and often accompany bone loss, raising the risk of falls and fractures.

You lift a case into the overhead locker and your shoulder protests. A flight of stairs leaves you more winded than it once did. Standing up from the floor needs a hand on the couch. These shifts often begin quietly in your 40s.

Muscle loss after 40 is a normal part of ageing, not a personal failing or a lack of effort. Knowing why it happens, and what the science says about rebuilding it, changes what you can do next. Working with an accredited exercise physiologist turns that knowledge into a plan.

What Happens to Muscle From Around Age 40

From around age 40, most adults steadily lose muscle mass, and the decline follows a broad, predictable pattern, even though the pace differs from person to person:

Gradual Loss by the Decade

Most adults lose muscle slowly from around age 30 and more quickly after 50, according to Healthdirect’s overview of muscle loss. The Australian Institute for Musculoskeletal Science puts the typical rate at about 3% to 8% every decade, with the sharpest decline in the 60s and 70s. The exact figure shifts with your genes, activity and health, so treat it as a guide, not a fixed schedule.

Faster Loss for Some People

Several things push the loss beyond the typical rate. A sedentary routine is the biggest, because muscle that is rarely loaded is muscle the body sees little reason to keep. Eating too little protein has a similar effect, and undereating becomes more common with age as appetite drops. Long-term conditions such as diabetes, heart failure and kidney disease can accelerate it, and women often notice a sharper decline around menopause.

Early Signs in Everyday Tasks

The first clues are practical, not dramatic. You might grip a jar less firmly, walk a little slower, tire sooner on a hill or need a push on the armrest to rise from a low chair. None confirms anything alone, but together they are worth attention, not dismissal as simply getting older.

What Drives Muscle Loss With Age

Losing muscle with age is not one process but several stacked together, which is why strength can slip even when the scales barely move:

Fewer and Smaller Fibres

With age, both the size and the number of muscle fibres fall. The fast-twitch fibres that produce power are affected most, which is why quick, forceful movements often fade before slower ones. Fewer working fibres mean less force, and the muscle looks and feels smaller.

Reduced Response to Protein

Younger muscle builds readily from the protein in a meal and from a training session. Older muscle responds less strongly to both, a change called anabolic resistance, so it is broken down a little faster than it is replaced.

Declining Anabolic Hormones

Several hormones help build and maintain muscle, including testosterone, growth hormone and insulin-like growth factor 1 (IGF-1). Their levels drift down with age, weakening the daily signal to keep muscle. In women, the fall in oestrogen around menopause adds to this, which helps explain the steeper decline many notice at that stage.

Weaker Signals From Nerves

Muscle only works when nerves tell it to contract. Ageing reduces the number of motor nerve cells and the connections between nerve and muscle, so fewer fibres are recruited and unused ones can waste away. This loss of signalling is a major reason strength can drop earlier and faster than muscle size.

Higher Background Inflammation

Levels of inflammation in the body tend to creep up with age. This low-grade, constant inflammation has a breakdown effect on muscle tissue, tipping the balance further towards loss even in people who feel well.

Can You Rebuild Muscle After 40?

Age-related muscle loss responds to the right stimulus, and much of what fades can be rebuilt, within limits that depend on you:

Strength Training That Rebuilds

Strength training, also called resistance training, has the strongest evidence for slowing and partly reversing the decline. It loads muscles against weights, bands or body weight, which tells the body to keep and rebuild them, sharpens how nerves recruit the fibres, and prompts new protein to be made. Some of the earliest gains come from better nerve-to-muscle signalling, which is why strength can improve before size does. Australia’s physical activity guidelines recommend muscle-strengthening activity on at least two days a week, and regular activity is also linked to extended life expectancy. A general practitioner (GP) can confirm it is safe to begin if you have health concerns.

Protein That Supports Growth

Muscle rebuilds from the protein you eat, so training only pays off when protein intake is enough. Research points to roughly 25 g to 30 g of protein per meal, and a daily intake of about 1.0 g to 1.2 g for every kilogram of body weight, to help maintain muscle in older adults. These figures are general guidance, and the right amount depends on your size, health and how you train, so a clinician or dietitian can set targets that suit you.

Progress That Stays Realistic

Change is gradual, and it shows in what you can do more than in how you look. It depends on your starting point, consistency, health and program, so no single timeline fits everyone and no result is promised. Many people feel early differences within weeks as the nervous system adapts, while rebuilding visible muscle usually takes months of steady work. Judge it by everyday markers, steadier stairs, easier lifting and getting out of a chair without using your arms.

How Weak Muscles Affect Your Joints

Muscle supports and protects the joints it surrounds, so when it weakens, the effects show up in specific places:

Weak Muscles and the Knee

The muscles at the front and back of your thigh steady the knee and absorb load with every step. As they weaken, more force passes through the joint itself, which can worsen stiffness and pain in knee osteoarthritis. Building strength around the knee is a core part of managing that condition and protecting the joint over time.

Weak Muscles and the Hip

The muscles around the hip and buttock keep the pelvis level and the joint stable when you walk, climb or stand on one leg. Weakness here is linked with the symptoms of hip osteoarthritis and with gluteal bursitis and tendon pain on the outer hip. Strengthening these muscles supports the joint and can ease the load that drives the pain.

Weak Muscles and the Skeleton

Muscle and bone tend to weaken together, a pairing sometimes called osteosarcopenia. Loading muscle also loads bone, so the same training that rebuilds strength helps maintain bone density, while losing both at once raises the risk of falls and fractures. Many people with low muscle mass also have thinning bones, which is why a strong bones program can matter alongside general strengthening.

Strength That Keeps You Moving After 40

Muscle loss from 40 is a normal chapter of ageing, not a verdict on the years ahead. The same biology that lets muscle fade also lets it answer to loading and good nutrition, well into later life.

Acting on it usually starts with an honest look at your current strength, a program matched to your body, your health and the activities you want to hold onto, and steady progress you can feel in ordinary tasks. The aim is not a number on a scan, but keeping the freedom to move through your life on your own terms.

If you have noticed your strength slipping and want a plan shaped around your circumstances, the team at MTP Health can talk you through whether exercise physiology is the right fit for you.

Frequently Asked Questions (FAQs)

1. How is muscle loss or sarcopenia diagnosed?

A doctor usually starts with your history and a few simple checks, such as how strong your grip is, how quickly you walk a short distance, and how easily you rise from a chair without using your arms.

A brief questionnaire known as SARC-F (screening for strength, assistance with walking, rising from a chair, climbing stairs and falls) can flag who needs closer assessment. To measure muscle itself, a dual-energy X-ray absorptiometry (DXA) scan is common, and it checks bone density at the same time.

2. Is it too late to start strength training in my 60s or 70s?

No. Muscle keeps responding to resistance training well into older age, and studies in adults in their 70s and 80s show gains in strength and daily function. Starting later still helps, with the program matched to your ability and built up gradually. Checking with your doctor first is sensible if you have existing health conditions.

3. Do I need a GP referral to see an exercise physiologist?

Not usually. You can see an accredited exercise physiologist without a referral, and at MTP Health you can book directly. A referral may still be needed for certain funding pathways, such as some Medicare or private health insurance arrangements, so it is worth checking what applies to your situation.

4. Can supplements such as creatine or vitamin D reverse muscle loss?

On their own, no. Australian health information notes there is not yet strong evidence that supplements like creatine, vitamin D or omega-3 rebuild muscle by themselves, though vitamin D may help some people, and a clinician can advise whether it suits you. The consistent finding is that resistance training with enough protein does the real work.

This article is general information only. It does not take your individual objectives, health situation or needs into account, and it is not a substitute for personal care from a qualified health professional. Speak with your doctor, an accredited exercise physiologist or another suitable practitioner before starting or changing how you exercise, eat or manage a health condition.