Training Tips

How to Work Out on a GLP-1 Without Losing Muscle

BUF Personal Training ·

A meaningful share of our clients are now losing weight on a GLP-1 medication — semaglutide, tirzepatide, whatever their doctor put them on. Five years ago this was a rare conversation. Now it comes up most weeks.

Before anything else: we're personal trainers, not doctors. Nothing here is medical advice, and nothing here is a recommendation to start, stop, or change a medication. That's between you and your prescriber. What we can talk about is the part that's actually our job — how to train and eat so that the weight you lose is the weight you wanted to lose.

That distinction turns out to be the whole game.

What the research actually shows

The loudest version of this story online is that GLP-1s "eat your muscle." That's an overstatement, and the real picture is more useful.

The most comprehensive look so far is a 2026 systematic review and meta-analysis in Drugs from a WHO Collaborating Centre group — 60 studies, 46 of them randomized controlled trials, covering more than 1.2 million people. Three findings matter here:

Lean mass does go down. Across 28 studies, GLP-1 use was consistently associated with a reduction in lean body mass and fat-free mass. This held up across every sensitivity analysis the authors ran. It's real and it's repeatable.

But it appears to be a weight-loss effect, not a drug effect. The authors concluded the lean mass changes "appeared largely related to weight loss" rather than to something the medication does to muscle tissue specifically. Lose weight quickly by any method and some of it comes off as lean mass. That has always been true. These drugs are unusually effective at producing weight loss, so they produce the lean mass loss that goes with it.

Bone was not affected. This is the part that surprises people. The meta-analysis found no significant effect on bone mineral density or fractures at any site. If you've read that GLP-1s wreck your bones, the current evidence doesn't support it.

The authors also flagged something worth repeating: the certainty of evidence was low, and whether the lean mass changes "translate into clinically meaningful impairments in muscle function or physical performance remains uncertain." A 2026 review in Maturitas focused on midlife and postmenopausal women made the same point — lean mass on a DEXA scan is not the same thing as muscle function, and very few trials have measured strength or physical performance directly.

So: a real, consistent signal, with honest uncertainty about how much it matters. Not a crisis, and not nothing.

Why we'd still train for it

Here's our position, and it's a practical one rather than a dramatic one.

Lean mass is the tissue that makes you strong, keeps you upright at 75, and does a disproportionate share of your glucose handling. Weight loss that preserves it leaves you better off than weight loss that doesn't. You are going to be at a lower body weight either way — the question is what composition you arrive at.

And the countermeasure is not exotic. It's the same two things we'd have told you before GLP-1s existed: lift, and eat enough protein.

The bone piece, properly framed

Since the GLP-1 evidence doesn't show a bone effect, the bone argument for lifting isn't about the drug. It's about the weight loss.

The cleanest data here is Villareal's 2017 trial in the New England Journal of Medicine: 160 older adults with obesity, six months, randomized to a weight-management program plus aerobic training, resistance training, combined training, or a control group. Every exercise group lost about 9% of body weight. What separated them was what came off with it.

Lean mass dropped 5% in the aerobic-only group, versus 3% with combined training and 2% with resistance training. Total hip bone mineral density dropped 3% in the aerobic group, versus 1% combined and 0.5% with resistance training. Same weight loss. Six-fold difference in bone loss, determined by what they did in the gym.

A 2023 trial in Experimental Gerontology found the same pattern for muscle itself. After adjusting for how much weight people lost, mid-thigh muscle area fell by 6.2 cm² with diet alone and 7.8 cm² with diet plus aerobic training — but 0.6 cm² with diet plus resistance training. Essentially preserved.

Bone responds to load. Cardio, walking, and the general activity of living in Manhattan are good for plenty of things, but they don't load the skeleton the way a loaded squat, hinge, or carry does. That's the case for resistance training during any significant weight loss, GLP-1 or not.

Protein: the hard part on a GLP-1

The training side is straightforward. Protein is where people on these medications actually struggle, and it's worth being blunt about why.

These drugs work largely by reducing appetite. That's the mechanism — it's not a side effect to work around, it's the point. But protein is the most filling macronutrient there is, and you're now operating with a fraction of your former appetite. People don't miss their protein target because they don't care. They miss it because they're full after six bites.

What the research used, for reference: the LEAN-PREP trial — a randomized controlled trial published in BMJ Open in 2026, specifically testing resistance exercise and protein in people starting semaglutide or tirzepatide — targets 1.6 g of protein per kg of body weight per day. Longland's 2016 trial in the American Journal of Clinical Nutrition pushed to 2.4 g/kg during a severe energy deficit with heavy training, and the higher-protein group gained 1.2 kg of lean mass while losing more fat than the lower-protein group. That was young men training six days a week for four weeks, so don't read it as a promise — read it as evidence that the direction matters a lot.

The exact number for you is a conversation for your prescriber or a registered dietitian, particularly since the right target depends on your starting point. What we'll say from the floor is that the clients who hold onto their strength through a GLP-1 are, without exception, the ones who treat protein as the non-negotiable part of every meal.

Tactics that actually work when you're not hungry:

  • Protein first, every meal. Eat it before anything else on the plate. When you stop after six bites, make those six bites count.
  • Drink some of it. Shakes, Greek yogurt, cottage cheese, skyr. Liquid and soft foods go down when solid food won't.
  • More meals, smaller. Four or five small protein hits beat three meals you can't finish.
  • Front-load the day. Appetite is usually best in the morning and worst in the evening, especially in the days right after a dose.
  • Track it for two weeks. Not forever — just long enough to find out what you're actually eating. Almost everyone is lower than they think.

We wrote more on the general principles in Nutrition for NYC Strength Trainees.

How to structure the training

Nothing here is specific to GLP-1s, which is rather the point. Good training is good training.

Two to three full-body sessions a week. Not five. You're in a substantial energy deficit with a suppressed appetite, which is a poor environment for recovery. Three quality sessions you recover from beat five you don't. Our take on this in general is in How Often Should You Strength Train?

Build around compound lifts. Squat and hinge patterns, horizontal and vertical pressing, horizontal and vertical pulling, loaded carries. These are what load the most muscle and the most bone per minute spent.

Progress the load. This is the single most-skipped piece. Muscle is retained by giving it a reason to stay, and that reason is mechanical tension that doesn't get easier over time. If the weight on the bar in month four looks like month one, you're doing maintenance cardio with dumbbells. Expect your rate of progress to be slower than it would be at maintenance calories — but the direction should still be up, or at minimum holding.

Keep cardio, but don't let it replace lifting. Walking is excellent and you'll get a lot of it in this city. It just doesn't do the job above. In Villareal's trial, the aerobic-only group lost the most lean mass and the most bone.

Expect bad days and train around them. Nausea, fatigue, and low energy are common, particularly after a dose increase. The useful move is to reduce volume rather than skip — fewer sets at your working weight preserves the training stimulus far better than missing the week. This is one of the real advantages of training with a coach: somebody else adjusts the session in real time instead of you deciding at 6am whether you feel up to it.

What we're still waiting to learn

The honest state of play: we have strong evidence that resistance training and higher protein preserve muscle and bone during weight loss generally, and good evidence that lean mass declines on GLP-1s. What we don't yet have is a large completed trial testing the combination specifically.

That's being run now. LEAN-PREP randomized 232 adults starting semaglutide or tirzepatide into four groups — control, resistance exercise, protein supplementation, or both — with MRI-measured quadriceps cross-sectional area as the primary outcome. Notably, the exercise arm is three sessions a week, progressing from one to three sets across the major muscle groups. That's close to what we'd program anyway, and we'll be reading the results closely.

The short version

The medication handles appetite. It does not decide what kind of body you end up with — your training and your protein intake do.

If you're on a GLP-1 and you lift two or three times a week with real progression, and you get your protein in, the research says you should arrive at the other end of this as a smaller, stronger version of yourself. If you lose the weight on cardio and willpower alone, you're likely to arrive smaller and weaker, with less bone than you started with. That's a choice available to you right now, and it gets harder to undo later.

If you want help building the training side of it, we're at 347 W 36th Street in Hell's Kitchen. Our rates are straightforward, every session is under $100, and you can get in touch here.

This article is general fitness information, not medical advice. BUF Personal Training is not a medical provider. Decisions about GLP-1 medications, dosing, nutrition targets, and whether any exercise program is appropriate for you should be made with your physician or another qualified healthcare professional.

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