Does losing weight increase VO2 max?
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The number goes up and the engine doesn’t. VO2 max is per kilogram, so losing 10 percent of your weight raises it about 11 percent with the same heart. Only training raises the oxygen your heart and blood can deliver.
People lose 20 pounds, see their watch’s VO2 max jump, and conclude they’ve become fitter. In a real sense they have, since every step and every stair now lifts less weight. But the heart, the blood and the muscles that set your top oxygen use haven’t changed at all. The watch is reporting new math on the same engine.
We’d count a lower weight as a real gain in the number and still train for the engine, because only training raises how much oxygen you can use, and that part stays with you whatever the scale does.
The math
VO2 max in ml/kg/min is the liters of oxygen you use in a minute, divided by your weight. Think of a car’s horsepower divided by its weight. Take some weight out of the car and the ratio rises, with the same engine under the hood.
A 200-pound man in his 40s at 35 uses about 3.2 liters of oxygen a minute, which puts him at about the 49th percentile. At 180 pounds with the same heart, he’s at 38.9, about the 63rd percentile, and above average. Losing 10 percent of your weight always lifts the number by about 11 percent (1 divided by 0.9). Slide the weight in the tool below to see it.
The Dallas five, in reverse
Five healthy men in Dallas were tested at 20 in 1966, then again at 50. The table follows them across those 30 years and six months of training after.
| At 20 | At 50 | After 6 months of training at 50 | |
|---|---|---|---|
| Weight | 77 kg (170 lb) | 100 kg (220 lb) | Not reported |
| Liters a minute | 3.3 | 2.9 | 3.3 |
| ml/kg/min | 43 | 31 | 36 |
Their engines lost only 11 percent in liters a minute. The per-kilogram number fell 28 percent, mostly from the 23 kg (50 lb) they’d gained. Training brought the liters all the way back to their level at 20, but per kilogram they only got to 36, because they still carried more weight than at 20.
Why both halves count
The big studies that link fitness to long life used the per-kilogram number. In the Cleveland Clinic study of 122,007 people, fitness came from how far each person got on a treadmill, which depends on both engine and weight. A lighter body that moves more easily counts there.
The engine is what training builds. In healthy people, VO2 max is set mostly by how much blood the heart can pump, and training raises it by raising that.
When the weight lost includes muscle
Not all weight loss is fat. On GLP-1 drugs like Ozempic and Zepbound, about 25 to 40 percent of the weight lost is lean mass, and studies so far haven’t shown a gain in fitness. See does Ozempic lower VO2 max?, and the myth that losing weight makes you fitter.
What your result means, and what to do next
- Losing weight raises the number. Every hill gets easier, because you carry less up it.
- The engine stays the same size. Only training raises the liters of oxygen your heart and muscles can use.
- Keep the cardio while you lose weight, and lift twice a week, so the loss comes mostly from fat. Weight and VO2 max
- No gym? Start with walks, stairs and hills. If you want to, and if you can, the natural way builds both layers. How to increase VO2 max naturally
- Retest the same way in 8 to 12 weeks. Same test, same route or same watch. Believe a change of more than 2 to 4 points.
6 sources
- McGuire DK and others, A 30-year follow-up of the Dallas Bedrest and Training Study: I. Effect of age on the cardiovascular response to exercise, Circulation, 2001europepmc.org
- McGuire DK and others, A 30-year follow-up of the Dallas Bedrest and Training Study: II. Effect of age on cardiovascular adaptation to exercise training, Circulation, 2001europepmc.org
- Bassett DR and Howley ET, Limiting factors for maximum oxygen uptake and determinants of endurance performance, Medicine and Science in Sports and Exercise, 2000europepmc.org
- Liu Z, Weeldreyer NR and Angadi SS, Incretin receptor agonism, fat-free mass, and cardiorespiratory fitness: a narrative review, Journal of Clinical Endocrinology and Metabolism, 2025pmc.ncbi.nlm.nih.gov
- Mandsager K and others, Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing, JAMA Network Open, 2018pmc.ncbi.nlm.nih.gov
- Kaminsky LA and others, Updated reference standards for cardiorespiratory fitness measured with cardiopulmonary exercise testing (FRIEND), Mayo Clinic Proceedings, 2022mayoclinicproceedings.org
