Age, health and weight

Does Ozempic lower VO2 max?

By GyroscopeUpdated November 15, 20265 sources

Not on paper, since VO2 max rises as you lose weight. But 25 to 40 percent of the weight lost on GLP-1 drugs like Ozempic is lean mass, and studies so far show no fitness gain. Add cardio and lifting to the drug.

On a GLP-1 drug like Ozempic, Wegovy, Mounjaro or Zepbound, a watch’s VO2 max often climbs as the weight comes off, and it looks like the drug is making you fitter. The number is per kilogram, so it rises whenever weight falls. The open question is what happens to the engine underneath, the liters of oxygen your heart and muscles can use, and so far it doesn’t seem to grow.

We’d treat the drug as a chance to build fitness while the weight comes down, with cardio most days and strength training twice a week. The weight loss makes every workout easier, and the training makes sure the engine grows instead of shrinking.

What the drugs do to the number

Take a woman in her 40s who weighs 240 pounds and has a VO2 max of 22, about the 31st percentile for her age. Her heart and lungs deliver about 2.4 liters of oxygen a minute. If she loses 20 percent of her weight and those liters stay the same, her number becomes 27.5, about the 59th percentile. Same engine, lighter car, and she’s moved from below average to above average without her heart changing at all.

If part of what she lost was muscle, the liters may not stay the same, since muscle is where the oxygen gets used. Nobody has shown yet which way it goes for most people.

What the review found

In 2025, researchers at the University of Virginia reviewed what’s known about GLP-1 drugs and the GLP-1/GIP drugs like tirzepatide. About 25 to 40 percent of the weight lost on them comes from fat-free mass, which includes muscle, a rate they described as far faster than the normal loss of muscle with age. Clinical studies hadn’t shown an improvement in cardiorespiratory fitness, and the long-term effects of the lean mass loss are unknown.

The review didn’t find that the drugs lower fitness. On their own they just haven’t been shown to raise it, and the per-kilogram number can make fitness look better than it is.

What to add

If you want to, and if you can, start the natural way. Brisk walks, stairs and hills build the engine with no gym, and how to increase VO2 max naturally has the studies. Then add these.

• Cardio most days. Steady training raised VO2 max by about 4.9 points in 28 controlled trials, and intervals by about 5.5. That’s the part that grows the engine.
• Strength training at least 2 days a week, which the US guidelines ask of every adult, so the muscle you keep has work to do.
• Enough protein. bodyfat.guide has typical protein ranges and a page on GLP-1 drugs and muscle.

Nothing here is a reason to change your dose. That’s a conversation for your prescriber. For the drug-by-drug detail, see bodyfat.guide on GLP-1 drugs, and for the math, slide the weight in the tool below.