What happens to muscle after 30?
Muscle mass starts to fall in the fourth decade of life. A 2004 review of muscle and ageing puts the loss at approximately 3 to 8% a decade after the age of 30, and says the rate is higher still after 60. The name for the combined loss of muscle mass, strength and function is sarcopenia, and the review describes it as a fundamental cause of disability in older people.
Nothing about it is sudden. A few per cent a decade is invisible from one year to the next, which is why it tends to be noticed late: the stairs feel steeper, a heavy bag gets put down sooner, getting up from a low chair takes a push from the hands. The review lists hormonal change, changes in how muscle responds to food, and inactivity among the likely causes. Inactivity is the one anyone can test: a short spell of bed rest cuts muscle mass and strength even in young people.
Why does losing muscle matter?
Muscle is what gets a body out of a chair, up a step and back upright after a stumble. With less of it, falls become more likely. A 2019 analysis of 33 studies and 45,926 people aged 65 and over found that people with sarcopenia had higher odds of falling, an odds ratio of 1.60 in studies that looked at one point in time and 1.89 in studies that followed people forward, and higher odds of fractures, 1.84 and 1.71. Those are associations, so they do not prove that muscle loss caused each fall, but the pattern held across study types, sexes and continents.
Muscle is also active tissue. The researchers who scanned body composition in one of the major weight-loss trials gave their reason plainly: losing lean muscle may affect the energy the body uses at rest, and how well it moves.
The loss is gradual and the effects tend to show later in life, so the years in between are when there is most to protect.
How do doctors check for it?
There is no single blood test. The Asian Working Group for Sarcopenia, whose 2019 consensus is the reference used across Asia, defines it as low muscle mass together with low strength or low physical performance. Low strength means a handgrip under 28 kg for men or under 18 kg for women. Low performance includes taking 12 seconds or more to stand up from a chair five times. Muscle mass is measured with a DXA body scan or a bioimpedance device.
The same consensus describes "possible sarcopenia": low strength or low performance on its own, without a scan. It exists so that people can start lifestyle changes earlier, in primary care. A weak grip or a slow chair stand is worth acting on before any scan confirms it.
What counts as strength work?
The World Health Organization's 2020 guidelines ask every adult for muscle-strengthening activity at moderate or greater intensity, working all the major muscle groups, on 2 or more days a week. That sits on top of the aerobic target of 150 to 300 minutes of moderate activity a week. For people aged 65 and over, the guidelines add varied activity that emphasises balance and strength on 3 or more days a week, to keep function and prevent falls.
Strength work is anything that makes a muscle work against a load it finds hard: free weights or machines, resistance bands, body-weight moves such as sitting down to a chair and standing up again, step-ups, or push-ups against a wall or a counter. A gym helps, and it is optional. A practical sign of enough effort is that the last few repetitions of a set feel hard.
Carrying the shopping in from the car counts as loading muscle, and it is a good start. On its own it seldom covers all the major muscle groups on two days a week, which is what the guideline asks for.
Does it still work if I start late?
Yes, and the evidence is unusually consistent. A Cochrane review of progressive resistance training in older adults pooled 121 randomised trials with 6,700 participants. In most, people trained two to three times a week at high intensity for them. Training had a large effect on muscle strength and a moderate to large effect on getting up from a chair, with a smaller gain in walking speed. Serious adverse events were rare, though the authors note that side effects were poorly recorded in many trials.
One of the best-known trials is three decades old. In 1994, 100 frail nursing-home residents with an average age of 87 were randomised to resistance training, a nutritional supplement, both, or neither, for 10 weeks. Strength rose by 113% in those who trained, against 3% in those who did not. The supplement on its own changed none of the main outcomes.
Starting light and adding load as strength builds is the principle the trials used. The 2004 review notes that resistance training may not suit everyone without adjustment, for example with high blood pressure, so anyone with heart disease, uncontrolled blood pressure, recent surgery or painful joints should ask their doctor how to begin. A physiotherapist can set the starting load.
Where does protein fit, and do supplements help?
Protein is the raw material, and exercise is the signal to use it. The 2004 review summed up the early trials bluntly: commercial supplements or high-protein diets on their own had largely failed to increase muscle mass or strength, and adding them to resistance exercise had not beaten exercise alone.
Larger analyses since then give protein a modest supporting role. A 2018 meta-analysis of 49 trials in 1,863 healthy adults found that protein supplements added, on average, 0.30 kg of fat-free mass and 2.49 kg to the heaviest single lift over a training programme. The extra benefit was smaller in older people, and stopped growing beyond a total intake of about 1.6 g of protein per kilogram of body weight a day. One author had received support from a dairy council that also funded some of the trials reviewed.
For people over 65, an international expert group, PROT-AGE, recommends at least 1.0 to 1.2 g of protein per kilogram a day, at least 1.2 g for those who exercise, and 1.2 to 1.5 g for most people with an acute or chronic illness. The exception matters. People with severe kidney disease who are not on dialysis may need to limit protein, so kidney function should be known before intake goes up.
In practice that means some protein at each meal from ordinary food: eggs, fish, chicken, tofu, tempeh, beans, milk or yoghurt. A powder is a convenience. It does not replace the training.
Do Ozempic and Mounjaro cause muscle loss?
Any large weight loss takes some lean mass with the fat, whether it comes from dieting, surgery or medicine. Semaglutide (sold as Ozempic and, at its weight-loss dose, Wegovy) and tirzepatide (sold as Mounjaro) produce large losses, so the lean share was measured with DXA body scans in a group of participants in each of their main weight trials. Both trials were sponsored by the companies that make the medicines.
In STEP 1, the 68-week semaglutide trial, 140 participants were scanned at the start and the end. Weight fell 15.0% on semaglutide and 3.6% on placebo. On semaglutide, total fat mass fell 19.3% and total lean mass 9.7%. Because fat fell faster, lean mass made up a larger share of the body afterwards, by 3.0 percentage points. This was an exploratory analysis, reported as a conference abstract.
In SURMOUNT-1, the 72-week tirzepatide trial, 160 participants were scanned. On tirzepatide, weight fell 21.3%, fat mass 33.9% and lean mass 10.9%, against 5.3%, 8.2% and 2.6% on placebo. About three quarters of the weight lost was fat and a quarter lean mass, the same split on tirzepatide as on placebo.
Lean mass is not the same as muscle. A 2024 review points out that it also counts organs, bone, fluid and the water held in fat tissue, and that studies vary widely: in some, lean mass made up 40 to 60% of the weight lost, in others about 15% or less. Imaging studies suggest the muscle that remains may be in better condition, with less fat inside it. The same review says older age and more severe illness may affect who suits these medicines, because of the risk of sarcopenia.
What the pooled trials add on lean mass, and the other effects to expect, are in the side effects to plan for on weight-loss injections. How each medicine works is in Mounjaro (tirzepatide), explained, and how the two compare is in Ozempic vs Mounjaro.
What helps on a weight-loss medicine?
The medicine does not protect muscle on its own. Everyone in both trials, placebo groups included, also received diet and activity counselling, so the figures above describe weight loss with that support in place.
Two habits are the sensible response, and they are the ones the guidelines and the reviews point to. The first is strength training on at least 2 days a week, started early in treatment. The second is protein at every meal, which takes planning when appetite is low, because smaller meals make it easy to fall short.
Older adults, and anyone who is already weak, deserve a closer look before and during treatment. A weak grip or a slow chair stand is worth raising with the prescribing doctor, as is any kidney disease before protein goes up. What a doctor checks first is in before semaglutide (Ozempic) or tirzepatide (Mounjaro), and what happens to weight when treatment stops is in rebound weight after stopping.
At The Retreat Clinic, GLP-1 medicines are prescription-only and used only after a full assessment, as part of medical weight management.
What about the face and the skin?
Lifting builds the muscles it loads, in the legs, back, arms and trunk. It does not put back fat lost from the face. When weight comes off quickly, the cheeks and the area around the eyes can look hollower, and after larger losses the skin may not fully follow. What has been measured, and what helps, is in Ozempic face and Mounjaro face.
The short version
Muscle thins slowly from about 30 and faster after 60. Strength work on 2 or more days a week slows it at any age, and the trials include people in their eighties. Protein supports the training and does not replace it. On semaglutide or tirzepatide, part of the weight lost is lean mass, so the same two habits matter more.
