GLP-1 medicines and sarcopenia: what to prescribe and what to monitor

Lean body mass on a scan falls while a patient loses weight on a GLP-1 medicine, and that is not the same finding as sarcopenia. Sarcopenia is defined by low muscle strength, confirmed by low muscle quantity, and almost none of the drug trials measured strength at all. So the honest answer to the question clinicians are typing, glp 1 sarcopenia, is that the mass change is real and consistent, the functional consequence is unmeasured, and your job is to load the patient and measure the thing the trials did not.

If you are seeing a patient on semaglutide or tirzepatide, this is the prescribing and monitoring half of the topic. The patient-facing versions, including the mechanism, the home plan, the protein basics and what happens after stopping, are already written: start at strength training on GLP-1 medicines if that is what you need. Colleagues searching GLP-1 physical therapy usually want this page instead.

Does GLP-1 cause sarcopenia?

Not as the word is defined, and the best synthesis to date says so carefully. Beaudart and colleagues pooled 60 studies on musculoskeletal outcomes with GLP-1 receptor agonists, 46 of them randomized trials, covering more than 1.25 million people and the whole class from exenatide and liraglutide to semaglutide and tirzepatide.

The muscle finding needs reading closely. In the main muscle model, which pooled lean body mass and fat-free mass together across 28 comparisons and 1,765 people, mass fell: a standardized mean difference of -0.52 (95% CI -0.80 to -0.23), driven mainly by liraglutide and semaglutide against placebo, and it survived every sensitivity analysis the authors ran. Certainty of evidence for that result was low and heterogeneity was high, at 88 percent.

Then the picture breaks up. Restricted to the 4 studies and 242 people that reported fat-free mass on its own, there was no significant change, which the authors read as fat-free mass being preserved. In the 5 studies that measured skeletal muscle mass by bioimpedance it went up, and that signal came from the observational studies rather than the trials.

Bone and joint outcomes showed nothing: no effect on bone mineral density at any site, no effect on fractures, and no change in WOMAC pain, function or stiffness. Those null results are the better-evidenced half of the paper, rated high certainty for lumbar spine bone density and for fracture of any kind, and moderate for hip and femoral neck density, while every muscle outcome was low or very low.

The sentence to carry into a consultation is the authors' own. They report that whether the lean mass changes translate into clinically meaningful impairment in function remains uncertain, and they call for studies that actually measure muscle function, strength or performance. Their reading is that the lean mass reduction appeared largely related to the weight loss itself, which is what happens in any large energy deficit.

Set that against the size of the weight change and you can see why the question arose. In SURMOUNT-1, 2,539 adults without diabetes, with a body mass index of 30 or more or of 27 or more with a weight-related complication, lost a mean of 15.0 percent of body weight on 5 mg of tirzepatide, 19.5 percent on 10 mg and 20.9 percent on 15 mg over 72 weeks, against 3.1 percent on placebo, from a baseline mean weight of 104.8 kg (231 lb). Body composition in that trial was measured in a substudy of 160 of those participants, 124 on tirzepatide and 36 on placebo, scanned at baseline and at week 72, and that substudy is where every lean mass figure attributed to SURMOUNT-1 comes from. Its numbers are the ones patients read, so have them to hand. Weight fell 21.3 percent, fat mass 33.9 percent and lean mass 10.9 percent on tirzepatide, against 5.3, 8.2 and 2.6 percent on placebo, and about 75 percent of the weight lost was fat and 25 percent lean mass (Look 2025).

Read the last part of that sentence twice, because it is the clinically useful bit: the 75 to 25 split was the same on placebo. The subgroup analyses were post hoc and the work was funded and co-authored by the manufacturer, so treat the subgroup consistency as a weaker claim than the main one. What the split says is that losing a quarter of the weight as lean tissue is what a large energy deficit does, not what this class of drug does, which is also how the meta-analysis authors read their own result.

Do not carry that 75 to 25 across to the whole class, though, because the proportion is not fixed. The same report sets it beside the semaglutide scan substudy of STEP 1, where the split was nearer 60 percent fat to 40 percent lean (Look 2025). The STEP 1 paper itself reports the direction rather than the proportions in its main text: in its 140 scanned participants, total fat and visceral fat fell, lean mass fell in absolute kilograms, and the share of the body that was lean rose (Wilding 2021). The two trials used different drugs and different scans, and produced different amounts of weight loss, so quote each figure with its trial's name on it and not as a rule.

The definition is the part to hold on to. EWGSOP2 puts low muscle strength first among the criteria, ahead of muscle size, with grip strength below 27 kg (60 lb) in men or below 16 kg (35 lb) in women, or a five-times chair stand over 15 seconds, flagging probable sarcopenia (Cruz-Jentoft 2019). A GLP-1 agonist and sarcopenia appear in the same sentence online far more often than a patient on one of these medicines meets those criteria.

The definition cuts both ways, and that is the point of using it. A fall in lean mass on a scan does not make a diagnosis, and a patient whose grip or chair stand drops below those cut-offs meets the criterion for probable sarcopenia whatever the cause, which is a reason to measure rather than to reassure. The diagnosed condition has its own page, sarcopenia, and the patient-facing account of the mass question is on why muscle loss happens.

Resistance training on GLP-1 medicines: what to prescribe

No trial has tested a resistance training program in people taking semaglutide or tirzepatide, so anyone quoting a dose for this situation is borrowing one. Say that out loud, then borrow carefully and name the source.

The nearest trial evidence is the Lundgren study, which used liraglutide and not the newer medicines. After an 8 week low-calorie diet in which 195 adults lost a mean of 13.1 kg (29 lb), they were randomized for a year to a moderate to vigorous intensity exercise program with placebo, liraglutide 3.0 mg daily, both together, or placebo alone. Against placebo, weight change was 4.1 kg (9 lb) more with exercise, 6.8 kg (15 lb) more with liraglutide and 9.5 kg (21 lb) more with the combination. The combination cut body fat percentage about twice as far as either single treatment, and it was the only arm that improved HbA1c, insulin sensitivity and cardiorespiratory fitness.

For the dose itself, use the general and older adult prescriptions and say which one you used. The World Health Organization asks adults for muscle-strengthening work at moderate or greater intensity on 2 or more days a week (Bull 2020), and the ICFSR consensus for older adults sets 2 to 3 days a week, 1 to 3 sets of 8 to 12 repetitions over 8 to 10 muscle groups, ramping from 30 to 40 percent of a one-repetition maximum towards 70 to 80 percent (Izquierdo 2021). Many programs for this situation therefore start at 2 or 3 sessions a week, 2 to 3 sets of 8 to 12 repetitions, with the load climbing every week or two. Your physio will adjust this. Say what the borrowing leaves out as well: both documents were written for people who are not in a large energy deficit, neither was tested in anyone losing a fifth of their body weight, and that is the gap your monitoring has to cover rather than the dose.

The energy deficit is the reason to prioritize load over volume: a long circuit burns the appetite a patient does not have, while 20 minutes of three or four hard lifts protects the tissue you are worried about. And the medicine's own side effects set the floor, because nausea, early satiety and dehydration decide whether a session happens at all in the first weeks after a dose increase.

Those side effects also set a limit on what you can prescribe at all. A patient who cannot keep fluids down does not train that day, and a patient taking insulin or a sulfonylurea alongside the GLP-1 needs the low blood sugar line and their diabetes team's own plan before you add hard sessions, because exercise and those two medicines pull the same way. The home versions are on exercises at home and the strength plan.

A warning about the dose you will find online. The one practitioner-facing article that ranks on these searches publishes a weekly session count, a repetition range and a load review interval with no citation of any kind. It may well be sensible, and it is not evidence, so do not hand it to a patient as though it were.

What should you measure, and how often?

Measure function and strength, because the drug trials measured mass and the mass number is the one that misleads. Lean mass on a scan includes organs, body water and bone as well as muscle fiber, so it moves for reasons that have nothing to do with the tissue the patient is worried about.

Measure	Why it earns a place	Interval
Grip dynamometry	The EWGSOP2 entry criterion, and quick	Baseline, then every 2 to 3 months
Five-times chair stand or the 30 second chair stand	Leg strength and the task patients notice first	Baseline, then every 2 to 3 months
Gait speed over 4 m	The performance measure that marks severity	Baseline, then every 3 to 6 months
Load and repetitions in the log	The only direct record of training stimulus	Every session
Weight and the rate of loss	Context for everything above, and a prescriber flag if it is faster than planned	Each visit

The 30 second chair stand test is the easiest of these to give a patient to repeat at home, and the outcome measures guide covers how to choose between the rest. Write the numbers in the note, not just the impression, because the only way to answer the patient's question in six months is to have measured it in month one. Older patients start from a lower base and have less in reserve, which is the point of GLP-1 and older adults.

What about GLP-1 sarcopenic obesity?

This is the phrase that most often belongs to the patient in front of you, and it has agreed criteria. The ESPEN and EASO consensus defines sarcopenic obesity as excess adiposity together with low muscle mass or function. Screening applies to people with a raised BMI or waist circumference who also carry risk factors, clinical signs or a positive questionnaire for low muscle mass or function. Diagnosis then assesses muscle function first and body composition second, and patients are staged as stage I with no complications or stage II where complications of the altered body composition or muscle dysfunction are present (Donini 2022).

That order, function before composition, is what makes the pathway usable in physiotherapy. It means a clinic with a dynamometer and a stopwatch can do the first half of the pathway, and it means a normal-looking weight trajectory does not rule the problem out. Where the screen is positive, the referral is to the medical team or a dietitian for the composition and the metabolic work, with the loading program running in parallel and not waiting on them.

Bone deserves one line here too. The pooled evidence showed no effect of these medicines on bone density or fracture, but rapid weight loss in general is not neutral for bone, so a patient already told their bone density is low belongs on the osteoporosis program with their prescriber informed.

What sits outside physiotherapy scope

Everything about the medicine itself. Whether to start one, which one, what dose, how long to stay on it, whether to pause or taper it to protect muscle, and how it interacts with anything else the patient takes: all of that belongs to the prescriber and the pharmacist. Never stop or change a prescribed medicine on your own. Put that line in what you give the patient; it does no work sitting in your own head.

Protein is the other boundary. There is no established daily target for people on these medicines, so do not invent one; that is a dietitian's referral, and the general picture without a number is on protein and exercise basics. Weight regain after stopping is a common question in the clinic and has its own page, after stopping the medicine, and the patient-facing framework for the whole topic is muscle loss on GLP-1 medicines.

Licensing differs between the USA, the UK, Canada, Australia and New Zealand, so which medicine is approved for whom and under which name is a question for the patient's own prescriber, not for us.

Warning signs to give the patient

These are the lines we put in front of patients on these medicines, word for word. Copy them rather than writing your own.

1. Emergency: if chest pain, pressure or tightness does not ease quickly when you rest, spreads to your arm, neck, jaw, stomach or back, or comes with sweating, feeling sick, feeling light-headed or being short of breath, call emergency services straight away, as this can be a heart attack. If it eases quickly and none of these happen, get medical advice the same day, and do not exercise again until you have been checked.
2. Emergency: sudden severe stomach pain together with pain spreading to your back, bloating that will not settle, a fast heartbeat, trouble breathing, or skin around your belly button, waist or upper outer thigh that looks blue or bruised (this can be harder to see on brown or black skin). Call emergency services or go to an emergency department, and do not drive yourself. If that sudden severe pain does not go away or keeps coming back, or comes with a high temperature or chills, without any of the signs above, get an urgent medical appointment or call your health service's urgent advice line the same day.
3. Same day: you feel dizzy, lightheaded or faint as you get up. Sit back down and wait for it to pass. If it does not pass within a minute or two, or it keeps happening, get medical advice the same day before you practice again. If you faint, or it does not settle within a few minutes of keeping still, call emergency services.
4. Same day: dizziness or feeling faint during or after exercise, without any of the emergency signs above. Stop the exercises and get medical advice the same day. If you faint, it does not settle within a few minutes of sitting still, or you cannot stand or walk steadily, call emergency services.
5. Same day: shakiness, sweating, tingling lips, hunger, a pounding heartbeat, blurred vision, feeling weak or confusion during or after a session, if you take insulin or other diabetes medicines. These can be signs of low blood sugar, and the risk of it is higher when insulin or a sulfonylurea is taken alongside one of these medicines. Treat it the way your diabetes team has told you, then contact them or your prescriber the same day. If someone cannot be woken, cannot swallow safely or has a seizure, call emergency services.
6. Same day: you cannot keep fluids down, you are being sick or have diarrhea that will not settle, you are peeing less than usual or your pee is dark yellow and strong smelling, you feel unusually tired, you feel dizzy when you stand up, or you are breathing quickly or your heart is racing. Contact your prescriber or get medical advice the same day, as these can be signs of dehydration. Call emergency services or go to an emergency department if your skin, lips or tongue look blue, gray, pale or blotchy (on brown or black skin this can be easier to see on the palms of the hands or soles of the feet), your skin feels cold, you are breathing fast or finding it hard to breathe, you are confused, or you are unusually sleepy or hard to wake.
7. Same day: back pain after a minor fall or strain if you are older, have low bone density (osteoporosis) or have taken steroid tablets for a long time. Get medical advice the same day.
8. Within a day or two: losing weight without trying, for example weight coming off faster than you and your prescriber expected, or weight that keeps coming off after you no longer want it to. See your doctor within a day or two and mention it. Tell your prescriber as well, and do not change a medicine on your own.
9. Within a few days: strength that is clearly going backwards, for example you need your hands to get out of a chair when you did not before, your grip gives out on jars and door handles, or you are stumbling on stairs. See a doctor or physio within a few days so someone can measure it rather than guess. Tell your prescriber as well, and do not change a medicine on your own.

In PocketPhysio the warning lines and your own cue sit beside each exercise, so the dizziness line travels with the standing work rather than sitting on a separate sheet. The program goes out as a link, by SMS or email, or into the Pocket Physio Care app, and WhatsApp is one option as well.

The short version

Lean body mass falls on these medicines in the main pooled model, at low certainty and with no agreement between the different ways of measuring the tissue, and no pooled analysis has shown a matching loss of strength because the trials did not look. Prescribe 2 or 3 resistance sessions a week with the load climbing, borrow the dose from the general and older adult guidelines and say that is what you did, and measure grip, chair stand and gait speed rather than body composition. Use the sarcopenic obesity criteria when the patient fits them, because function comes first in that pathway and a physiotherapy clinic can do that half. Leave every question about the medicine itself with the prescriber.

References

1. Beaudart C, Malréchauffé Y, van Heden S, et al. GLP-1 receptor agonists and musculoskeletal outcomes: a systematic literature review and meta-analysis. Drugs. 2026;86(10):1661-1691. https://doi.org/10.1007/s40265-026-02365-3
2. Cruz-Jentoft AJ, Bahat G, Bauer J, et al. Sarcopenia: revised European consensus on definition and diagnosis. Age and Ageing. 2019;48(1):16-31. https://doi.org/10.1093/ageing/afy169
3. Donini LM, Busetto L, Bischoff SC, et al. Definition and diagnostic criteria for sarcopenic obesity: ESPEN and EASO consensus statement. Clinical Nutrition. 2022;41(4):990-1000. https://doi.org/10.1016/j.clnu.2021.11.014
4. Lundgren JR, Janus C, Jensen SBK, et al. Healthy weight loss maintenance with exercise, liraglutide, or both combined. New England Journal of Medicine. 2021;384(18):1719-1730. https://doi.org/10.1056/NEJMoa2028198
5. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine. 2022;387(3):205-216. https://doi.org/10.1056/NEJMoa2206038
6. Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine. 2021;384(11):989-1002. https://doi.org/10.1056/NEJMoa2032183
7. Look M, Dunn JP, Kushner RF, et al. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study of adults with obesity or overweight. Diabetes, Obesity and Metabolism. 2025;27(5):2720-2729. https://doi.org/10.1111/dom.16275
8. Izquierdo M, Merchant RA, Morley JE, et al. International Exercise Recommendations in Older Adults (ICFSR): Expert Consensus Guidelines. Journal of Nutrition, Health and Aging. 2021;25(7):824-853. https://doi.org/10.1007/s12603-021-1665-8
9. Bull FC, Al-Ansari SS, Biddle S, et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine. 2020;54(24):1451-1462. https://doi.org/10.1136/bjsports-2020-102955
10. NHS. Low blood sugar (hypoglycaemia). Page last reviewed 3 August 2023. https://www.nhs.uk/conditions/low-blood-sugar-hypoglycaemia/
11. NHS. Acute pancreatitis. Page last reviewed 11 March 2026. https://www.nhs.uk/conditions/acute-pancreatitis/
12. NHS. Dehydration. Page last reviewed 1 May 2026. https://www.nhs.uk/conditions/dehydration/

Written and checked by the PocketPhysio editorial team. Last updated 2026-10-26.