research shows runners on Ozempic or Zepbound lose mostly fat but also some muscle, and many move less each day. Ozempic (semaglutide) and Zepbound (tirzepatide) are appetite-suppressing incretin drugs, and performance can hold up if runners keep lifting and stay active.
Lean mass includes muscle plus water and other nonfat tissue, not only biceps. For runners, that tissue matters for hills, finishing kick and injury resistance. The split in 2026 is not drug versus diet, but training versus no training.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Table of Contents
- How much muscle is lost?
- Why do runners move less?
- Can strength and running hold up?
- How do runners protect muscle?
How much muscle is lost?
A 2026 systematic review of 20 trials with 15,782 participants tracked the lean share of weight loss. Lean mass made up 35.2% with semaglutide, 25.4% with tirzepatide and 26.8% with liraglutide, according to the systematic review in Diabetes, Obesity and Metabolism. That pattern looks much like dieting alone.
The same review found lifestyle-only loss was 26.2% lean, not significantly different from the drugs. In that review, lifestyle plus resistance training cut the lean share to about 17.5%. For a runner who loses 20 pounds, a 25% lean share means 5 pounds of lean tissue. At 17.5%, that drops to 3.5 pounds.
Why do runners move less?
In 753 adults with obesity tracked with Fitbits, daily steps fell from 5,047 to 4,487 after starting semaglutide, tirzepatide, liraglutide or dulaglutide. Moderate-to-vigorous activity fell from 28 to 22 minutes per day, according to Gizmodo reporting on the ENDO 2026 study. Study lead Dr.
Sajana Maharjan warned the drugs reduce both fat and lean muscle. Fox News, reporting the Endocrine Society release, quoted her advice to preserve activity and exercise rather than rely on the drug alone. For runners, six fewer hard minutes daily plus 560 fewer steps adds up fast. One skipped midweek run plus one flat long run can dull aerobic fitness.
Can strength and running hold up?
News-Medical reported a March 2026 animal plus 12-week human pilot study with a better signal. Semaglutide and tirzepatide reduced fat while grip strength held. Treadmill-running performance was also preserved. Gizmodo noted an important limit on the activity finding.
It was a preliminary ENDO 2026 conference presentation using retrospective All of Us and Fitbit data. It was not a peer-reviewed trial of running performance in runners. Mass and function can diverge. Scale weight may show muscle loss while legs still produce force on hills and intervals.
How do runners protect muscle?
A 2026 narrative review in Healthcare concludes adults on or stopping semaglutide or tirzepatide should use structured aerobic plus resistance exercise to preserve muscle and maintain loss, according to the 2026 narrative review in Healthcare. Running supplies the aerobic part, but most runners need added loading.
Book lifts like runs and log them. Two short sessions beat one skipped long session.
- Run on schedule, then add two full-body resistance sessions weekly
- Track steps and hard minutes so a slide shows early
- Keep hill sprints, strides or short intervals to hold power
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