Jump to: Why Mounjaro affects exercise | Starting when energy is low | Preventing muscle loss | Managing physical challenges | The mental side | Your gradual exercise plan | Practical tips | Take home message
Exercise can feel significantly harder when taking Mounjaro. Research shows that fatigue affects up to 10% of people taking the medication1, while many more report reduced energy levels when their body is adapting to the medication.
Important safety information: Mounjaro (tirzepatide) is a prescription-only medication for treating type 2 diabetes and managing obesity. This article is for informational purposes only. Always consult with your healthcare provider before starting any new medication, particularly if you have had your gallbladder removed or have other health conditions.
The medication slows gastric emptying and reduces calorie intake, which can temporarily impact our energy for physical activity.
Plus, many people may eat too little on Mounjaro, further contributing to their feelings of fatigue on the medication.
This article will reveal why Mounjaro can lead to feelings of tiredness and fatigue, and how to introduce exercise to support your health and weight loss while on the medication.
Why Mounjaro makes exercise feel harder
When you’re eating less energy, our brain tries to conserve energy by making exercise feel harder than usual; a protective response that helps to protect existing energy stores.
Think of it like your phone switching to power-saving mode when the battery runs low. Your body does something similar, making high-intensity exercise feel unnecessarily difficult even though you’re physically capable.
Additionally, the slowed digestion can cause discomfort during activity, whilst rapid weight loss can temporarily affect how your heart and muscles respond to exercise.
Common exercise-related effects include:
- Feeling exhausted at lower exercise intensities
- Our brain hitting the ‘stop’ button earlier than usual
- Stomach discomfort during activity
- Needing longer recovery between workouts
- Generally feeling like exercise is much harder
These effects typically peak within 48-72 hours of injection and often improve as your body adapts to each dose level and finds its new balance.
Starting when energy is low: the if/then approach
Second Nature’s behaviour change programme uses if/then planning to help manage challenging situations.
Having these plans ready means you don’t have to make a decision; you just do it.
- If I feel too tired for my planned workout, then I’ll do 5 minutes of walking instead
- If I have injection-day fatigue, then I’ll do seated exercises while watching TV
- If the gym feels overwhelming, then I’ll do a 10-minute YouTube workout
- If I experience nausea during exercise, then I’ll switch to gentle stretching or yoga
- If my usual routine feels impossible, then I’ll do 10 wall push-ups
Adding in this flexibility helps prevent the all-or-nothing approach of thinking that all exercise needs to hard and long to be worth it.
Research shows that any movement helps preserve muscle mass during weight loss3, and all movement is good for our health, so you should celebrate all the movement you do.
Preventing muscle loss: the minimum effective dose
During rapid weight loss on Mounjaro (average 15-20% of body weight)2, preserving muscle becomes crucial.
From a nutritional perspective, it’s essential to eat protein in every meal to support this, but with exercise, we need far less exercise than you might think.
Studies show that just two 15-minute strength sessions each week can help maintain muscle mass during weight loss3. Focus on compound movements:
- Bodyweight squats (or seated leg extensions)
- Wall or modified push-ups
- Resistance band rows
- Modified planks (even 10 seconds counts)
Aim for 2-3 sets of 8-12 repetitions. When starting out, start with one set and gradually progress. Maintaining consistency is better than trying to do too much and ending up doing nothing at all.
Managing physical challenges on Mounjaro
There’s no perfect time for exercise, as everyone will respond differently to the medication. Still, here are some tips if you’re struggling to find the right time:
- Energy is often lowest 24-48 hours post-injection
- Morning exercise may work better before gastric effects peak
- Wait 2-3 hours after eating to avoid discomfort
- Hydration becomes even more critical
For those experiencing joint discomfort (a reported side effect), low-impact options include:
- Swimming or water walking
- Stationary cycling
- Chair-based exercises
- Yoga or gentle stretching
- Resistance band work
Realistic expectations
Weight loss with Mounjaro isn’t linear, especially when adding exercise. The scale might not reflect your efforts immediately due to:
- Water retention from muscle repair
- Muscle gain offsetting fat loss
- Natural weight fluctuations
- Hormonal changes
Notice other improvements besides weight loss:
- Energy levels throughout the day
- Strength improvements (even small ones)
- Fitness levels
- How easy you find daily activities like taking the stairs
- Sleep quality
- Mood stability
Your gradual exercise plan
Here’s a gentle progression that prioritises sustainability over speed:
| Timeframe |
Primary focus |
Activities |
If you’re feeling more confident |
| Weeks 1-4 |
Any movement counts |
• 5-minute daily walk
• Gentle stretching in bed
• Standing during TV adverts
• Deep breathing exercises |
• 10-minute walks
• Chair-based exercises
• Light household tasks |
| Weeks 5-8 |
Building a habit |
• 10-minute daily movement
• Choose activities you enjoy
• 2-3 days that feel easy
• Rest when needed |
• 15-20 minute walks
• Bodyweight exercises
• Try a beginner YouTube workout |
| Weeks 9-16 |
Finding your rhythm |
• 15-minute sessions
• 3-4 days per week
• Mix different activities
• Include one strength session |
• 30-minute activities
• Add a second strength session
• Try a class or sport |
| 4-6 months |
Sustainable routine |
• 20-30 minutes movement
• 3-4 days feels normal
• Activities you look forward to
• Listen to your body |
• 4-5 days if it feels good
• Increase intensity (not duration)
• Set performance goals |
| 6 months+ |
Long-term lifestyle |
• Movement is part of your routine
• 3-4 days minimum
• Focus on consistency
• Celebrate maintaining this |
• Build toward specific goals
• Try new challenges
• Help others get started |
Important reminders:
- Staying at any phase indefinitely is perfectly fine
- Some weeks you might move backwards – that’s normal
- Three days of exercise you enjoy are better than six days of forced exercise
The goal isn’t to become a fitness enthusiast. It’s about finding a movement you can maintain for life, even after stopping Mounjaro.
Practical tips
Based on Second Nature’s experience supporting members on Mounjaro:
Start below your capacity. If 10 minutes seems reasonable, begin with 5.
Track consistency over intensity. Mark calendar days you moved, regardless of duration.
Stack habits. Link movement to existing routines, like doing calf raises while the kettle boils, or walking after meals.
Take home message
While exercise on Mounjaro may feel more challenging initially, you should find it easier as your body adapts to the medication and your fitness levels begin to improve.
Focus on movement that feels sustainable with your current energy levels. Some days that might be a full workout; others might be five minutes of stretching.
Most people find their energy comes back as they get used to the medication. Until then, consistency matters more than intensity.
Second Nature's Mounjaro and Wegovy programmes
Second Nature provides Mounjaro or Wegovy as part of our Mounjaro and Wegovy weight-loss programmes.
Why choose Second Nature over other medication providers, assuming you're eligible?
Because peace of mind matters.
We've had the privilege of working with the NHS for over eight years, helping people across the UK take meaningful steps toward a healthier, happier life.
Our programmes are designed to meet people where they are, whether that means support with weight loss through compassionate one-to-one health coaching, or access to the latest weight-loss medications (like Mounjaro and Wegovy) delivered alongside expert care from a multidisciplinary team of doctors, psychologists, dietitians, and personal trainers.
At the heart of everything we do is a simple belief: real, lasting change comes from building better habits, not relying on quick fixes. We're here to support that change every step of the way.
With over a decade of experience, thousands of lives changed, and a long-standing record of delivering programmes used by the NHS, we believe we're the UK's most trusted weight-loss programme.
We hope to offer you something invaluable: peace of mind, and the support you need to take that first step.
References
- Wilding, J. P., et al. (2021). Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine, 384(11), 989-1002.
- Jastreboff, A. M., et al. (2022). Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine, 387(3), 205-216.
- Wadden, T. A., et al. (2021). Effect of subcutaneous semaglutide vs placebo as an adjunct to intensive behavioral therapy. JAMA, 325(14), 1403-1413.
- National Institute for Health and Care Excellence. (2023). Tirzepatide for managing overweight and obesity. Technology appraisal guidance [TA924].
- Kosiborod, M. N., et al. (2023). Semaglutide in patients with heart failure and obesity. New England Journal of Medicine, 389(12), 1069-1084.
