If you're taking Mounjaro or another GLP-1 weight-loss medication, there's a good chance the number on the scales has become an important measure of your progress.
And understandably so.
For many people, these medications can make losing weight considerably easier by reducing appetite and helping them feel fuller for longer.
But while seeing the scales move in the right direction can be encouraging, there's something else worth paying attention to.
What exactly are you losing as your weight comes down?
Because when we lose weight, we don't necessarily lose body fat alone. Some of that weight can also come from muscle and other lean tissue.
And that's why strength training deserves a place in your weight-loss journey.
Whether you're taking Mounjaro, Wegovy or another medication that works through GLP-1 pathways, maintaining your strength and fitness should be part of the bigger picture.
Let's look at why.
How Do Mounjaro and Other GLP-1 Medications Work?
Mounjaro and Wegovy are prescription medications used for weight management in eligible patients.
They work by influencing hormonal pathways involved in appetite and feelings of fullness.
Mounjaro contains tirzepatide, which acts on two hormone receptors: GIP and GLP-1.
Wegovy contains semaglutide, which acts on the GLP-1 receptor.
Although they work slightly differently, both can help people reduce their food intake and lose weight.
However, these medications aren't intended to replace healthy lifestyle habits.
NICE recommends that weight-management medications are used alongside appropriate dietary changes and increased physical activity.
And that's particularly important when it comes to protecting your muscle mass and maintaining long-term fitness.
Can You Lose Muscle While Taking Mounjaro or Other GLP-1 Medication?
Yes, muscle and other lean tissue can be lost during weight loss, including when using GLP-1-based medications.
But it's important to put this into perspective.
Losing lean mass isn't unique to Mounjaro or Wegovy. It can happen whenever someone loses a significant amount of weight, whether that's through medication, dietary changes or other methods.
One study published in Diabetes, Obesity and Metabolism in 2025 examined changes in body composition among people taking tirzepatide in the SURMOUNT-1 clinical trial.
Researchers found that approximately 75% of the weight lost was fat mass, while around 25% was lean mass.
That doesn't mean everyone taking Mounjaro will lose a quarter of their weight as muscle.
Lean mass includes muscle, but also water, organs and other non-fat tissue. The proportions vary between individuals, and the study wasn't designed to determine how much actual skeletal muscle was lost.
Nevertheless, the findings highlight an important consideration.
Successful weight loss shouldn't just be about becoming lighter. It should also be about maintaining strength, fitness and physical function.
And resistance training is one of the most useful tools available to help achieve that.
Why Is Maintaining Muscle So Important During Weight Loss?
Muscle does much more than influence how your body looks.
It plays an important role in movement, physical independence and metabolic health.
When you're losing weight, maintaining muscle can help you continue feeling strong and capable as your body changes.
1. Helps Maintain Strength
Think about the everyday activities you want to continue doing comfortably.
Walking upstairs, carrying shopping, gardening, playing with your children or grandchildren, or simply getting up from the floor.
All these activities depend, to some extent, on muscular strength.
If you lose a significant amount of muscle during weight loss, you may find some physical activities more difficult.
Strength training helps provide the stimulus your muscles need to maintain their strength, even when you're eating fewer calories.
2. Supports a Healthier Body Composition
There's an important difference between losing weight and improving body composition.
Weight loss simply means becoming lighter.
Body composition refers to how much of your body is made up of fat, muscle and other tissues.
Two people can lose the same amount of weight but experience very different changes in their body composition.
If your goal is to reduce body fat while maintaining as much muscle as possible, strength training should be part of your approach.
3. Supports Metabolic Health
Muscle is an important tissue involved in how your body uses and stores glucose.
Maintaining muscle mass can support metabolic health and physical function.
Muscle also contributes to the amount of energy your body uses at rest, although the effect is sometimes exaggerated in fitness marketing.
Building or maintaining muscle isn't a magic solution for speeding up your metabolism, but it is an important part of long-term health.
4. Helps You Stay Active as You Get Older
Maintaining muscle becomes increasingly important with age.
As we get older, we naturally become more susceptible to losing muscle mass and strength, particularly if we're inactive.
For people in their forties, fifties and beyond who are losing weight with medication, resistance training can help address this additional challenge.
The aim is to emerge from your weight-loss journey not only lighter, but also physically capable and confident.
Why Strength Training Matters When Taking Mounjaro or Other GLP-1 Medication
When people think about exercising to lose weight, cardio is often the first thing that comes to mind.
Walking, cycling, swimming and running are all excellent activities.
But strength training offers something particularly valuable during weight loss.
It gives your muscles a reason to remain strong.
When you perform resistance exercises, your muscles are challenged to produce force.
Over time, and with appropriate progression and recovery, this helps maintain or improve muscular strength.
During a period of reduced calorie intake, resistance training can help limit the loss of muscle and support physical function.
It's not a guarantee that you'll preserve every bit of muscle, but it can make an important contribution.
And the good news is that you don't need to spend hours in the gym.
What Strength Exercises Should You Do While Taking GLP-1 Medication?
For many people, two or three full-body strength sessions each week can provide a good foundation.
You can train at home using your bodyweight, resistance bands or dumbbells.
A balanced programme should include exercises that challenge your major muscle groups.
For example:
Squats or sit-to-stands: Strengthen your legs and help with everyday movements.
Lunges or step-ups: Challenge your legs, hips and balance.
Press-ups or chest presses: Strengthen your chest, shoulders and arms.
Dumbbell or resistance-band rows: Work your upper back and arms.
Hip bridges or hip hinges: Strengthen your glutes and the muscles involved in hip movement.
Core exercises: Help improve trunk strength and control.
You don't need to perform every exercise in every session.
The important thing is choosing movements appropriate to your fitness level and gradually making them more challenging as your strength improves.
If you're completely new to resistance training, starting with a small number of exercises and focusing on good technique is perfectly sensible.
What About Walking and Cardio?
Strength training is important, but it shouldn't be your only form of exercise.
Walking, cycling, swimming and other cardiovascular activities offer benefits for heart health, stamina and general wellbeing.
Walking is particularly accessible and can be a good starting point if you're returning to exercise after a period of inactivity.
UK physical activity guidelines recommend that adults work towards at least 150 minutes of moderate-intensity aerobic activity each week, alongside muscle-strengthening exercise on at least two days.
However, these are general recommendations, not targets you need to achieve immediately.
If you're experiencing fatigue, nausea or other side effects from medication, your activity may need adjusting.
Start at a manageable level and build gradually.
Why Eating Enough Protein Matters
Mounjaro and other GLP-1-based medications can significantly reduce appetite.
While this can help with weight management, it can also make eating enough food and getting the nutrients your body needs more challenging.
Protein is particularly important because it provides the building blocks your body uses to maintain and repair muscle.
Good protein sources include:
Chicken, turkey and lean meat.
Fish and seafood.
Eggs.
Greek yoghurt and other dairy products.
Beans, lentils and chickpeas.
Tofu and other soya products.
Try to include protein regularly throughout the day rather than relying on one large meal.
However, there's no single protein target that's appropriate for everyone taking GLP-1 medication.
Your needs depend on factors including your body size, activity level, age and medical history.
If you're struggling to eat enough, experiencing persistent nausea or unsure how much protein you need, speak to your prescribing healthcare professional or a registered dietitian.
And remember that protein alone isn't enough.
Your body also needs adequate overall nutrition, including carbohydrates, fats, vitamins, minerals and fluids.
What If You Feel Too Tired or Sick to Exercise?
Some people experience side effects when taking Mounjaro or other GLP-1 medications.
These can include nausea, vomiting, diarrhoea, constipation and fatigue.
They may be particularly noticeable when starting treatment or following a dose increase.
If you're not feeling well, there's no benefit in forcing yourself through a demanding workout.
You may need to reduce the intensity, shorten the session or take some time to recover.
A gentle walk or light movement might be appropriate on some days, but don't push through significant symptoms.
If you're vomiting, unable to maintain adequate hydration, feeling faint or experiencing persistent or severe symptoms, seek medical advice.
Severe abdominal pain, particularly if persistent, also requires urgent medical assessment.
Exercise should support your health, not become another source of stress.
What Could a Weekly Exercise Routine Look Like?
If you're taking Mounjaro or another GLP-1 medication and want to introduce more structure to your exercise, here's an example of a balanced week.
Day - Activity
Monday - Full-body strength workout
Tuesday - Brisk walk or gentle cycling
Wednesday - Rest or light mobility
Thursday - Full-body strength workout
Friday - Walking or other comfortable cardio
Saturday - Longer walk or an activity you enjoy
Sunday - Rest or gentle movement
This is an example rather than a prescribed routine.
The amount and intensity of exercise should reflect your current fitness, health, medication tolerance and recovery.
If you're new to exercise, start with shorter sessions and gradually build up.
Don't Measure Your Progress by Weight Alone
When you're taking weight-loss medication, it's understandable that the scales become a major focus.
But they're only telling you part of the story.
You can also measure progress through:
Improvements in muscular strength.
Being able to walk further or climb stairs more comfortably.
Better cardiovascular fitness.
Improved balance and mobility.
Feeling more confident during everyday activities.
Building consistent exercise and nutrition habits.
You might find that your weight loss slows at certain points while your strength and fitness continue to improve.
That doesn't mean you're failing.
It means there are other important ways your health and fitness can progress.
Frequently Asked Questions About Mounjaro, GLP-1 Medication and Exercise
Can you exercise while taking Mounjaro?
Yes. Regular physical activity is generally encouraged as part of weight management with Mounjaro. However, exercise should be appropriate to your health, fitness and medication tolerance. Speak to your healthcare professional if you're experiencing significant side effects or have medical concerns.
Does Mounjaro cause muscle loss?
Weight loss with Mounjaro can include a reduction in lean mass, which includes muscle and other non-fat tissue. This isn't unique to Mounjaro, and it doesn't mean everyone will experience substantial muscle loss. Resistance training and adequate nutrition can help support muscle maintenance.
Is strength training better than cardio when taking GLP-1 medication?
Both are valuable. Strength training is particularly useful for maintaining muscle and strength, while cardiovascular exercise supports heart health, stamina and overall fitness. A balanced programme should ideally include both.
How often should I lift weights while taking Mounjaro?
For many adults, two full-body strength sessions per week are a sensible starting point. Your programme can be adjusted according to your experience, fitness and recovery.
Can I build muscle while losing weight on Mounjaro?
It's possible, particularly if you're new to strength training or returning after a break. However, building muscle during weight loss can be more challenging, especially when calorie intake is significantly reduced. Maintaining muscle and improving strength are worthwhile goals in their own right.
Do I need to join a gym?
No. You can follow an effective strength training programme at home using bodyweight exercises, resistance bands or dumbbells. The key is selecting appropriate exercises and gradually increasing the challenge.
Will exercise help keep the weight off if I stop taking Mounjaro?
Regular exercise, particularly a combination of strength training and cardiovascular activity, can support long-term weight management. However, weight regain is common after stopping GLP-1-based treatment, and exercise cannot guarantee that lost weight will stay off. Any decision about stopping medication should be discussed with your prescriber.
Weight Loss Is Only Part of the Journey
Mounjaro and other GLP-1 medications can be valuable tools for people who need support managing their weight.
But achieving a lower number on the scales shouldn't be the only goal.
Maintaining your muscle, improving your strength, building cardiovascular fitness and developing sustainable habits are all important parts of looking after your health.
And those are things you can work on throughout your weight-loss journey.
You don't need extreme workouts, expensive equipment or hours in the gym.
You need an approach that suits your current fitness, challenges you appropriately and fits into your life.
Because losing weight is one thing. Staying strong, fit and healthy as you do it is just as important.
Stay Strong with Epic Fitness Online Coaching
At Epic Fitness, we believe successful weight management should be about more than the number on the scales.
Our online fitness coaching focuses on helping you build strength, improve fitness and develop exercise habits that work around your lifestyle.
Whether you're taking Mounjaro or another GLP-1-based weight-loss medication, or simply looking for a structured approach to exercise, we can help you work towards your fitness goals.
With personalised workouts, guidance and ongoing accountability, you can build a routine that supports your progress from home or wherever you prefer to train.
Ready to focus on strength as well as weight loss? Get in touch with Epic Fitness to find out more about our online coaching.
This article provides general fitness information and is not medical advice. Epic Fitness does not prescribe, recommend or manage GLP-1 medications. Always follow advice from your prescribing healthcare professional, particularly if you experience side effects, have diabetes or other medical conditions, or need individual nutrition support.
Sources and Further Reading
NHS England. Weight Management Injections - information on Mounjaro, Wegovy and the importance of physical activity and balanced nutrition.
NICE (2025, updated 2026). Overweight and Obesity Management — Physical Activity and Diet - recommendations on sustainable activity and nutritional balance.
NICE. Tirzepatide for Managing Overweight and Obesity (TA1026) - guidance on using tirzepatide alongside dietary changes and increased physical activity.
Look, M. et al. (2025). Body Composition Changes During Weight Reduction With Tirzepatide in the SURMOUNT-1 Study - clinical trial analysis of changes in fat and lean mass.
American Diabetes Association (2026). Pharmacologic Treatment of Obesity in Adults: Standards of Care in Overweight and Obesity. - discusses resistance training, protein intake and muscle preservation during medication-supported weight loss.