GLP-1 medications have transformed obesity management, but their effectiveness also highlights the importance of prioritising exercise while using them. For decades, the common advice has been to eat less and exercise more to lose weight. Medications like Wegovy address the first part by reducing hunger, leading to weight loss. But what about exercise? Should we still go to the gym if these medications help us lose weight? How do they affect our ability to work out?
It’s becoming clear that for those using these medications, exercise might be even more important than for others. Rapid weight loss from semaglutide (see “How they work”, below) often leads to significant muscle mass loss. A 2021 study of 95 overweight or obese patients on semaglutide found that their average lean body mass dropped by about 10% after 68 weeks.
Lean body mass includes both muscle and bone. These medications cause people to consume fewer calories, leading the body to break down muscle, fat, and bone for energy. “Up to 40% of the weight loss from semaglutide could be from muscle mass loss,” says Grace Kulik of the University of Colorado. This muscle loss isn’t exclusive to weight-loss medications; it also occurs with very restricted diets and bariatric surgery.
Loss of Muscle
The impact of muscle loss on strength and function isn’t immediately clear. Kulik and her team studied the psoas muscle, located in the lower back, in 51 semaglutide users. After 24 weeks, muscle volume dropped by more than 9%, but muscle function didn’t significantly change. Kulik suggests that weight loss may make some tasks easier, thus compensating for the muscle loss.
For older adults, who are already more vulnerable to muscle and bone loss, further research is needed to understand how these medications affect physical performance. Katsu Funai of the University of Utah notes that those on weight-loss drugs may be at a higher risk of falls.
Semaglutide’s effect on athletes is also under scrutiny. The World Anti-Doping Agency added semaglutide to its monitoring programme to assess its potential performance-enhancing effects and ensure athlete health isn’t compromised.
Exercise to Prevent Weight Regain
Physical exercise seems vital in preventing weight regain, which is a common issue for people who stop taking these medications. In a 2024 clinical study, 98 obese individuals took the GLP-1 medication liraglutide. Half of them also engaged in a supervised exercise programme. One year after treatment ended, those in the exercise group regained 2.5 kilograms, while the non-exercise group regained 6 kilograms.
Torekov believes the difference is due to those in the exercise group maintaining active habits after the programme ended. Physical activity likely helped them preserve muscle mass. “When you lose muscle mass, you naturally burn less energy, making it more difficult to maintain weight loss,” she explains.
Given this, individuals using weight-loss medications should prioritise exercise. Torekov recommends at least two hours of vigorous exercise each week to preserve muscle and bone mass.
Incentive to Exercise
The problem is that these medications may reduce motivation to exercise. Research in mice has shown that those given semaglutide ran about half the distance on a wheel compared to the control group. In another experiment, the mice were required to press a lever to unlock a wheel. The semaglutide-treated mice pressed the lever 25% fewer times, suggesting reduced motivation to exercise.
These results may be due to side effects like nausea, which could make exercise less appealing, or because semaglutide affects the brain’s reward pathways. Medications like Ozempic, which suppress food cravings, may also dampen other urges, including the desire to exercise.
However, humans are more complex than mice. Research shows that people often become more active after rapid weight loss, such as after bariatric surgery, likely due to improved mobility and better physical function.
We may still be learning about how weight-loss medications influence fitness, but what’s clear is that exercise remains vital. Hitting the treadmill and lifting weights will help maintain overall health, even with the aid of weight-loss medications.
How They Work
Drugs such as semaglutide (sold as Wegovy for weight loss and Ozempic for diabetes), liraglutide (sold as Saxenda and Victoza), and exenatide (sold as Byetta) mimic the actions of glucagon-like peptide-1 (GLP-1), a hormone that promotes satiety and stimulates insulin production, lowering blood sugar levels.
These GLP-1 receptor agonists reduce hunger, leading to significant weight loss when used long-term. Recently, tirzepatide (sold as Mounjaro and Zepbound) has also come onto the market, which mimics GLP-1 and another satiety hormone, GIP.
