Ozempic and Your Muscles: How to Protect Your Strength on GLP-1 Medication

Ozempic, Wegovy and Mounjaro have gone from specialist diabetes medications to something half of Johannesburg seems to be talking about. We are seeing more patients who are on one, and for many of them it has been life-changing. People who have struggled with their weight for years are finally losing it.

Some of them also tell us they feel weaker than they expected. Stairs are harder work and they tire quickly in the gym. A few have also picked up new back, hip or knee niggles along the way.

Losing weight takes load off your joints, which is a good thing. Losing a lot of muscle at the same time is not, and most of that muscle loss can be avoided with the right approach.

How GLP-1 medications work

Semaglutide (Ozempic and Wegovy) and tirzepatide (Mounjaro) copy hormones that your gut releases after a meal. They slow down how quickly your stomach empties, reduce your appetite and help control blood sugar. You end up eating a lot less without the constant hunger that usually derails a diet.

The results are impressive. In the STEP 1 trial, people on semaglutide lost an average of 14.9% of their body weight over 68 weeks, compared with 2.4% on placebo (Wilding et al., 2021). In SURMOUNT-1, the average loss on tirzepatide was 21.3% over 72 weeks (Look et al., 2025). Until recently you would only have expected numbers like that after weight-loss surgery.

Not all of the weight lost is fat

Whenever you lose weight, you lose some lean mass along with the fat. Lean mass is mostly muscle, but it also includes organs, bone, water and connective tissue.

In the STEP 1 participants who had detailed body composition scans, about 38% of the weight lost on semaglutide was lean mass (Mozaffarian et al., 2025). In SURMOUNT-1 it was about 25% on tirzepatide, with the other 75% coming from fat (Look et al., 2025). Across all the studies the figure varies a lot, from around 15% to 40% or more (Neeland et al., 2024).

To be fair to the medications, you still lose proportionally much more fat than muscle, so overall body composition usually gets better. Some researchers think the worry about muscle loss has been overblown for most people (Conte et al., 2024), and there is some evidence that the muscle you keep may actually be of better quality, with less fat stored inside it (Neeland et al., 2024).

The concern is mainly for older adults and people who did not have much muscle to begin with, who are at higher risk of sarcopenia (Neeland et al., 2024). Sarcopenia is age-related loss of muscle mass and strength, and it is closely linked with falls, fractures and losing independence later in life. If you are in your 50s or 60s, or were fairly inactive before starting, you have less muscle to spare.

Why we care about your muscle

Muscle takes load off your joints. Strong quads protect your knees, strong glutes keep your hips and pelvis stable and a strong trunk supports your lower back. When muscle is lost, your joints pick up more of the work.

Muscle is also where your body stores and burns most of its glucose, and it accounts for a good share of the calories you use at rest. The less of it you have, the easier it is to put weight back on.

Then there is bone. Muscles pulling on bone are one of the main things that keep your skeleton strong, and rapid weight loss without strength training can lead to bone loss. A trial using liraglutide, an older GLP-1 medication, showed this clearly. People who took the drug alone lost bone density at the hip and spine, while those who combined it with exercise kept their bone density, even though they lost almost 17 kg (Jensen et al., 2024).

Good news if you have sore knees

For people with knee osteoarthritis, the weight loss can make a big difference. The STEP 9 trial followed 407 people with obesity and painful knee arthritis for 68 weeks. The semaglutide group lost 13.7% of their body weight and their knee pain score fell by 41.7 points out of 100, compared with 27.5 points in the placebo group (Bliddal et al., 2024). Their physical function improved as well.

Add the strengthening exercise that osteoarthritis guidelines already recommend and you give your knees the best chance.

How to hold on to your muscle

In 2025, four large American medical and nutrition organisations published a joint advisory on supporting people who take GLP-1 medications (Mozaffarian et al., 2025). Most of it comes down to two things: strength training and protein.

Strength train at least three times a week

The advisory recommends that GLP-1 medications be prescribed alongside a structured exercise programme, with strength training at least three times a week and at least 150 minutes of moderate aerobic exercise a week to protect muscle and bone.

It also makes the point that eating more protein will not preserve muscle on its own if you are not doing resistance training. Your body holds on to muscle that it is using.

Squats (or sit-to-stands if you are starting out), hip hinges, pushing and pulling movements, lunges and loaded carries cover most of what you need. The weight should be heavy enough that the last few reps of each set feel hard, and it should increase gradually over the weeks. If you are new to this, start light and get the technique right first.

Eat enough protein

When your appetite is suppressed, protein is often the first thing to drop. The advisory notes that intakes of around 1.2 to 1.6 g of protein per kilogram of body weight per day have been proposed during active weight loss, or roughly 80 to 120 g a day for most adults (Mozaffarian et al., 2025). Spread it across your meals and eat the protein part of your plate first when you are not very hungry.

If you have kidney disease or another medical condition, check your protein target with your doctor or a dietitian.

Keep training once the weight is off

Exercise helps you keep the weight off too. In one trial, people who combined a GLP-1 with regular exercise after losing weight reduced their body fat percentage about twice as much as those using either the medication or exercise alone (Lundgren et al., 2021). In the year after treatment stopped, the people who had exercised regained significantly less weight than those who had only taken the medication (Jensen et al., 2024).

That matters, because most people put weight back on when they stop. In the STEP 1 extension, participants had regained about two-thirds of the weight they had lost within a year of coming off semaglutide (Wilding et al., 2022). Muscle you build while on the medication, and the habit of training, stay with you after you stop.

Trials testing resistance training alongside semaglutide or tirzepatide are still running, and we will update this article when the results come out.

Where we come in

Your medication is managed by your GP or endocrinologist, not by us. What we can do is make sure your body is able to handle the training that protects your muscle, bones and joints.

A lot of people starting a GLP-1 have not exercised properly in years. Some already have low back pain, knee pain, hip pain or arthritis and are nervous about lifting weights. Others go at it too hard and too soon, then get injured.

When you come to see us, we will look at how you move and pick up any stiff joints, weak areas or old injuries that need attention before you start loading them. If you are in pain, we treat it with chiropractic adjustments, mobilisation, dry needling or soft tissue work so it does not hold you back. We then set you up with a strength programme through our rehabilitation exercises that starts where you are and progresses from there, and we deal with niggles early so a sore knee does not undo months of good work.

The goal is to come off the medication lighter and stronger, rather than lighter and weaker.

When to book in

It is worth seeing us if:

You are about to start, or are already on, a GLP-1 medication and want to protect your muscle
You feel noticeably weaker or more tired since you started
Back, hip or knee pain is stopping you from exercising
You want to start strength training but are not sure how
You have lost a lot of weight and want to keep it off

Get in touch or book an appointment at our Sandton practice and we will help you build the strength to make the weight loss last.

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