Strength Training on GLP-1s: Why It Matters

GLP-1 medications such as semaglutide and tirzepatide have changed what weight loss can look like. But the scale reports only one number. It cannot tell you how much of what you lost was fat and how much was muscle and other lean tissue.

That is where strength training comes in. This guide explains what body-composition studies found on GLP-1s, why muscle matters, what US guidelines recommend and how to start safely. It draws on the STEP 1 and SURMOUNT-1 DXA substudies, the 2025 joint nutrition advisory from four US obesity and nutrition societies, the federal Physical Activity Guidelines, the 2026 American College of Sports Medicine (ACSM) position stand and peer-reviewed reviews.

Educational only. This is general information, not a personal exercise prescription. If you have heart disease, diabetes, joint problems, osteoporosis, are pregnant or have any other medical condition, check with your clinician before starting or changing an exercise program.

The short answer: weight loss on a GLP-1 includes some lean mass. Strength training (also called resistance training) is the best-supported way to protect muscle while you lose fat. US guidelines recommend working all major muscle groups on at least 2 days a week, and the 2025 GLP-1 nutrition advisory suggests at least 3 strength sessions a week plus regular aerobic activity, adjusted to your fitness level. Pair it with enough protein, start light and progress gradually.

What is strength training?

Strength training is any exercise that makes your muscles work against resistance. The Physical Activity Guidelines for Americans describe it as activity that “overloads” muscles, making them do more work than they are used to. Their examples include lifting weights, resistance bands, push-ups and planks, carrying heavy loads and heavy gardening.

Two terms you will see in GLP-1 research:

• Lean mass: everything that is not fat (and, in many DXA reports, not bone mineral). It includes muscle, but also organs, water and connective tissue.
• DXA (dual-energy X-ray absorptiometry): a low-dose scan that estimates fat mass, lean mass and bone. The 2025 joint advisory calls it a gold standard for body composition, though it is costly and not done often.

Do GLP-1 medications cause muscle loss?

Yes, some lean mass is lost, but the picture is more nuanced than social media headlines suggest. Here is what the trial body-composition data show.

Semaglutide: the STEP 1 DXA substudy

In STEP 1, 140 participants had DXA scans at the start and at week 68. On semaglutide 2.4 mg, body weight fell by 15.0% on average. Total fat mass fell 19.3% and total lean mass fell 9.7%. Because fat dropped faster than lean tissue, the proportion of lean mass in the body rose by 3.0 percentage points. Placebo produced no major changes.

The 2025 joint advisory summarizes STEP 1 differently, in kilograms: of an average 13.6 kg (about 30 lb) lost, 8.3 kg (62%) was fat and 5.3 kg (38%) was lean mass. Because muscle makes up about half of lean mass, the advisory estimates that roughly 20% of the total weight lost was muscle.

Tirzepatide: the SURMOUNT-1 DXA substudy

In a SURMOUNT-1 substudy of 160 participants scanned at baseline and week 72, tirzepatide reduced body weight by 21.3%, fat mass by 33.9% and lean mass by 10.9%. About 75% of the weight lost was fat and 25% was lean mass. Strikingly, the placebo group, which lost much less weight, showed the same 75/25 split, and the proportions held fairly steady across sex, age and weight-loss subgroups.

Study (DXA substudy)	Total weight change	Fat mass change	Lean mass change	Share of loss that was lean
STEP 1, semaglutide 2.4 mg, 68 weeks	−15.0%	−19.3%	−9.7%	~38% (advisory summary)
SURMOUNT-1, tirzepatide (pooled doses), 72 weeks	−21.3%	−33.9%	−10.9%	~25%
SURMOUNT-1, placebo, 72 weeks	−5.3%	−8.2%	−2.6%	~25%

Different analyses report slightly different numbers, but the message is consistent: most of the weight lost is fat, and a meaningful minority is lean tissue.

Is this a GLP-1 problem or a weight-loss problem?

Mostly a weight-loss problem. The joint advisory notes that the drop in fat, lean and muscle mass tracks with how much weight is lost, and is similar to what is seen with bariatric surgery and very low-calorie diets. It adds that lean-mass loss is also affected by how severe the calorie restriction is, how fast weight comes off, and whether someone does strength training. Low protein intake from a reduced appetite can add to the problem.

Without structured strength training, modeling cited in the advisory suggests muscle accounts for about 10–15% of weight lost in women and 20–25% in men.

Why muscle matters when you lose weight

Losing fat is the goal, so why worry about a few kilograms of lean tissue? Because muscle does a lot of quiet work:

• Physical function. Muscle lets you climb stairs, carry groceries, get up from a chair and keep your balance.
• Long-term health. The joint advisory states that low or decreasing muscle and bone mass is linked to physical impairment, falls and fractures, surgical complications, lower quality of life and reduced survival.
• Bone. The advisory notes that substantial (≥14%) and rapid (over 3–4 months) weight loss is associated with significant bone loss, with older adults and women at greater risk.
• Aging. In a 2024 Diabetes Care review, researchers estimated that the roughly 6 kg of lean mass lost on newer incretin drugs is comparable to the effect of a decade or more of aging on muscle. That is the authors’ estimate, not a measured outcome.

The advisory also lists groups at higher risk of muscle loss and sarcopenia (age-related loss of muscle and strength): older adults, people who are perimenopausal or postmenopausal, people with low testosterone, and those who are sedentary or do no resistance training.

On X, a common worry is ending up with “a smaller but fatter body.” Many replies, including from clinicians, land on the same answer: protein plus strength training.

What can strength training actually do?

It limits lean-mass loss during dieting

The strongest data come from diet-based weight-loss studies, not GLP-1 trials. A 2018 meta-analysis of six randomized trials in older adults with obesity found that adding resistance training (three times a week, for 12 to 24 weeks) to calorie restriction prevented 93.5% of the lean-mass loss seen with diet alone. Fat loss and total weight loss were similar with or without training.

The 2024 Diabetes Care review adds that supervised resistance programs lasting more than 10 weeks can produce large increases in lean mass (about 3 kg) and strength (about 25%) in men and women.

Strength work beats aerobic exercise for muscle

The joint advisory states that structured resistance training, or mixed resistance plus aerobic training, is well established to help preserve lean mass during weight loss, while aerobic activity alone has a smaller effect. It also cautions that extra protein alone is likely inadequate to preserve muscle without structured strength training.

What we know with GLP-1s specifically

Direct evidence is still thin:

• The advisory cites a randomized trial in which one year of GLP-1 therapy plus exercise preserved bone mineral density, while GLP-1 therapy alone reduced it.
• In a well-known trial of liraglutide, an older GLP-1 drug, adding an exercise program improved weight-loss maintenance compared with either alone. That program was mostly aerobic, not strength-focused.
• As of the 2024 Diabetes Care review, no published trials had tested individually tailored resistance training combined with incretin drugs such as semaglutide or tirzepatide. The authors still recommended it, based on strong evidence from diet, obesity and diabetes research.

So the honest summary is: strength training is strongly supported in principle, widely recommended, and low-risk for most people, but GLP-1-specific trials are still catching up.

How much strength training is recommended?

Official guidance is consistent on the basics and differs a little on frequency. Here is how the main sources compare:

Source	Strength frequency	Key details
Physical Activity Guidelines for Americans (HHS) and CDC	2 or more days a week	Moderate or greater intensity; work all major muscle groups (legs, hips, back, abdomen, chest, shoulders, arms); one set of 8–12 repetitions per exercise is effective, 2–3 sets may be more effective
ACSM position stand (2026)	At least 2 sessions a week	High effort, all major muscle groups; 2–3 sets per exercise helps strength; training to complete failure is not necessary; many forms (home, bands, machines, free weights) work
2025 joint GLP-1 nutrition advisory	At least 3 times a week	Plus at least 150 minutes of moderate aerobic activity a week; customize to fitness level and physical capacity

The federal guidelines add that exercises should be done to the point where another repetition would be difficult, and that gradual increases in weight, sets, repetitions or days build strength. Aerobic guidance for adults is 150 to 300 minutes a week of moderate activity, or 75 to 150 minutes of vigorous activity.

Most Americans are not there yet: ACSM cites self-report data showing only about 30% of US adults do muscle-strengthening activity at least 2 days a week, and nearly 60% do none. If you are starting from zero, you are not alone.

What does a sensible start look like?

The details belong to you, your clinician and ideally a qualified exercise professional; the joint advisory suggests an exercise physiologist or strength trainer to assess strength, set up a program and monitor it. Most beginner programs share the same building blocks:

1. Cover the main movement patterns. A squat or sit-to-stand, a hip hinge (such as a deadlift pattern or glute bridge), a push (wall or incline push-up, chest press), a pull (band or cable row), and a carry or core exercise. The ACSM authors suggest that upper- and lower-body push and pull movements are enough to target the major muscle groups.
2. Pick a resistance you can control. Body weight and bands are fine to start. Mayo Clinic suggests choosing a weight or band that tires your muscles in about 12 to 15 repetitions; the federal guidelines describe 8 to 12. Both are reasonable ranges for beginners.
3. Leave a rep or two in the tank. You want the last few reps to feel hard, but ACSM found training to complete failure is not needed for gains.
4. Rest muscle groups. Mayo Clinic recommends a full day of rest between sessions for the same muscle group.
5. Progress slowly. When the last reps start feeling easy, add a little weight, a set, or a few reps.
6. Protect your form. Stop any exercise that causes pain, and get coaching on technique if you are new.

Mayo Clinic notes that two sessions a week of about 20 to 30 minutes can be enough to notice stronger muscles. A full beginner routine is coming to our Exercise & Metabolism hub.

How do you train when appetite and energy are low?

This is one of the most common real-world questions. GLP-1s reduce appetite, and the joint advisory reports caloric intake reductions of 16–39% in people using them. Some side effects can also affect workouts. In the trial data summarized by the advisory, fatigue was reported by 11% on semaglutide 2.4 mg versus 5% on placebo, and 7% on tirzepatide 15 mg versus 3% on placebo. Dizziness was 8% versus 4% with semaglutide and 4% versus 2% with tirzepatide.

Practical ideas to discuss with your care team:

• Do not train on empty. A small, protein-containing snack an hour or two beforehand may help, if your stomach tolerates it.
• Hydrate. The advisory warns that dehydration from nausea, vomiting or diarrhea can cause acute kidney injury.
• Schedule around rough days. If symptoms cluster after your weekly dose or a dose increase, plan lighter sessions then. Our GLP-1 nausea guide covers why symptoms peak after dose changes.
• Shrink, don’t skip. On low-energy days, a single set of each exercise is still worthwhile.
• Watch for low blood sugar. The advisory notes that hypoglycemia can occur in people with type 2 diabetes, especially those taking insulin or sulfonylureas. If that applies to you, ask your prescriber how to handle exercise.
• Stop and seek help for chest pain, fainting, severe dizziness or shortness of breath that is out of proportion to the effort.

Our managing side effects guide covers symptoms more broadly.

How does protein fit in?

Training gives muscle a reason to stay; protein gives it the raw material. The joint advisory says sufficient dietary protein should be a priority, “particularly in combination with a structured strength training program.” We cover targets in detail in how much protein you need on a GLP-1, so here is just the headline: the advisory discusses higher intakes during active weight loss, often around 1.2–1.6 g per kg of body weight per day, or a practical 80–120 g a day, with personal adjustments for kidney disease and other conditions.

For meal ideas when appetite is low, see our high-protein eating guide and the nutrition hub.

Who should check with a clinician first?

Strength training is safe for most healthy adults. The ACSM position stand notes that in an analysis of more than 38,000 participants, exercise did not increase the risk of serious adverse events. Still, the federal guidelines say adults with chronic conditions or symptoms should be under the care of a health care provider and can consult a professional about the types and amounts of activity that suit them.

It is especially worth asking first if you:

• Have heart disease, high blood pressure that is not controlled, or chest symptoms with effort
• Have diabetes and take insulin or other medicines that can cause low blood sugar
• Have osteoporosis, a past fracture, or joint problems such as knee arthritis
• Are older, frail, or have noticed falls or loss of balance
• Are pregnant or postpartum

If a condition keeps you from meeting the full recommendations, the guidelines say to be as active as your abilities allow and avoid inactivity.

How do you know it is working?

The scale is a poor guide here, since muscle and fat both weigh something. More useful signs include:

• Strength progress: lifting a little more, or doing more reps, over weeks.
• Everyday function: easier stairs, standing up from a chair without using your hands, carrying bags.
• Simple tests: the joint advisory mentions sit-to-stand, stair climb and timed-up-and-go tests, and notes that one-rep-max testing is not recommended unless you are highly trained.
• Body composition: if your clinic offers it, bioelectrical impedance (BIA) or DXA can track lean mass over time.

The advisory recommends assessing muscle strength and function before starting a GLP-1, so ask whether a baseline check makes sense. Our first 30 days guide covers other things to set up early.

Common myths about strength training on GLP-1s

“The drug destroys muscle, so exercise is pointless.” The trial data show lean-mass loss that tracks with weight loss, much like other large weight-loss methods. Resistance training is the best-studied way to limit it.

“Protein alone will protect my muscle.” The advisory says it is likely inadequate without structured strength training.

What experts are saying in videos

Clinician-facing videos echo the published advice. In a short Medscape video, “Muscle Wasting With GLP-1 Agonists: A Pound of Prevention Is Worth a Pound of Cure,” the presenter recommends counseling on a nutrient-dense, high-protein diet and prescribing resistance or body-weight exercise. In a 2025 Healio video interview, Christos Katsanos, PhD, of Arizona State University and Mayo Clinic Arizona, names protein and resistance exercise as the two main strategies to help preserve muscle on GLP-1 drugs. Treat videos as education, not personal advice.

The bottom line

GLP-1 medications help most people lose substantial fat, but a meaningful share of the weight lost is lean tissue: about a quarter in the SURMOUNT-1 substudy and more in some STEP 1 analyses. Strength training is the best-supported way to protect muscle, strength and function. Work all major muscle groups at least twice a week, as federal guidelines advise, building toward the three sessions the GLP-1 nutrition advisory suggests, with regular aerobic activity and enough protein. Start where you are, progress gradually and loop in your clinician.

Keep exploring in the Exercise & Metabolism hub, read what a GLP-1 medication is, or plan for the long term in the plateaus and maintenance hub.

Medical disclaimer: Weightomics publishes general health information for education only. It is not a substitute for professional medical advice, diagnosis or treatment. Never start, stop or change a medication or exercise program without talking to a licensed clinician.