Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
You’ve just finished a session, felt the ‘post-workout glow’, and perhaps even pushed through those last few reps—only to step on the scale the next morning and see the number has climbed. It’s an incredibly common source of frustration, but before you let self-doubt creep in, let’s look at the science.
In fact, studies have found that strength and high-intensity workouts cause tiny muscle tears, leading your body to hold onto extra water while it repairs and rebuilds. That short-term water retention alone can bump the scale up for a few days, even when you’re burning fat and getting fitter. Your body is complex, and exercise affects muscles, water balance, hormones, and even food intake in ways that can make the scales bounce around.
Understanding why this happens can help you stay motivated and avoid giving up too soon. Let’s discuss why your weight might spike after a workout and why this ‘weight gain’ is actually a vital part of your progress towards a healthier metabolic set point.
When you challenge your body, it initiates a series of recovery protocols. While these are essential for building a healthier, stronger version of yourself, they often manifest as temporary fluctuations on the scale.
Resistance training and high-intensity sessions create microscopic micro-tears in your muscle fibres. To repair this tissue, your body triggers a natural inflammatory response, drawing extra fluid into the muscles to facilitate healing. This is a vital part of the strengthening process and a clear sign that your metabolic set point is shifting.
Your body stores carbohydrates as glycogen in muscles and liver to fuel workouts. Crucially, glycogen is ‘hydrophilic’—it loves water. For every gram of glycogen your body stores, it binds with approximately three grams of water. This is your body’s way of restocking its ‘fuel tank’ for your next session; it is energy, not fat.
Physical activity redistributes blood and fluids throughout your system. Furthermore, as you lose electrolytes through sweat, your body may signal a craving for salt. An increase in sodium intake, combined with exercise-induced fluid shifts, can cause your body to hold onto extra water temporarily as it works to maintain its internal balance.
It is perfectly natural to feel hungrier after a workout. However, your body can sometimes overcompensate for the energy burned. If post-workout snacks or liquid calories (like protein shakes and sports drinks) aren't balanced, you may experience a slight scale increase. This is often just the result of a higher volume of food and water in your system.
Vigorous exercise is a form of ‘healthy stress’ that temporarily raises cortisol levels. Cortisol can lead to short-term water retention and may even influence your cravings. This is a normal part of the biological protection mechanism and typically balances out as your body adapts to a consistent training routine.
Your weight is never a static number. It varies throughout the day based on hydration, food intake, and your body's waste cycles. Weighing yourself immediately after a workout, when your body is in the peak of its repair phase, will often give you an inaccurate picture of your long-term progress.
How your body responds to workouts also depends on your metabolism and daily habits. Read 10 Mistakes That Slow Down Your Metabolism to see if any common pitfalls could be masking your progress.
When the scale doesn’t reflect the effort you’re putting in, it’s easy for motivation to dip. However, long-term health is built on consistency, not day-to-day weight fluctuations. Here is how to keep your focus on the bigger picture:
Set realistic expectations: Weight loss and fitness gains take time. Don’t expect the scale to always move in your favour immediately after exercise. Focusing on realistic goals keeps you motivated and prevents discouragement. If you’re struggling with the pace of your progress, here is how to stay motivated even when you want faster results.
Focus on consistency over intensity: Regular, sustainable workouts are more effective than sporadic intense sessions. Consistency builds habits and long-term results, even if the scale doesn’t reflect changes right away.
Track non-scale victories: Notice improvements in strength, endurance, flexibility, or how your clothes fit. Non-scale victories remind you that progress isn’t always measured in kilograms.
Choose workouts you enjoy: Exercise should feel fun or at least satisfying. If you hate every minute of it, motivation will plummet. Enjoyable workouts make you more likely to stick with them.
Follow a simple routine: Keep your exercise schedule straightforward and manageable. Complex routines can be overwhelming and easy to skip, while a simple plan encourages consistency.
Schedule workouts like appointments: Treat your exercise sessions like important meetings. Writing them into your calendar makes it easier to commit and stay accountable.
Celebrate small wins: High-five yourself for completing workouts, improving reps, or hitting weekly goals. Celebrating little wins boosts motivation and keeps you moving forward.
Avoid daily scale checks: Daily weigh-ins can be misleading due to normal fluctuations in water, glycogen, and digestion. Weekly or biweekly checks provide a more accurate picture of progress.
Allow proper recovery: Rest days are part of training. Recovery helps muscles repair, reduces risk of injury, and prevents burnout, all of which support long-term progress.
Remind yourself why you started: Keep your bigger picture in mind: better health, strength, confidence, or energy. Reconnecting with your ‘why’ helps you push through temporary frustrations like post-workout scale spikes.
Gaining weight after a workout is almost always temporary and normal. Between water retention, glycogen storage, hormonal shifts, and increased appetite, your body’s scale can fluctuate day to day without reflecting real fat gain. By understanding these causes and focusing on consistency, recovery, and non-scale victories, you can stay motivated and on track toward your fitness goals.
It’s worth keeping in mind that the number on the scale is just one tiny snapshot of your overall progress. It doesn’t tell the full story of your strength, endurance, and health improvements.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.