Weight and your VO2 max
Your number is your engine divided by your weight. Slide the weight and watch the number and your rank move while the engine stays exactly where it was.
At 180 lb with the same heart, 35 becomes 38.9 (+11 percent): about the 63rd percentile for men in their 40s, group above average. The engine didn't change. The car did.
The number is liters a minute divided by your weight, so 10 percent less weight gives about 11 percent more with the same heart. Only training raises the liters.
Same engine, heavier car: the Dallas five
At 20 170 lb
At 50 220 lb
After six months of training
liters a minute ml/kg/min. Five healthy men tested at 20 and again at 50: the engine barely aged, the weight did, and six months of training brought the engine back (McGuire 2001).
On a GLP-1 drug, 25 to 40 percent of the weight lost is lean mass, and studies so far show no fitness gain, so the number rises while the engine doesn't (Liu and others, 2025). More on GLP-1 drugs and VO2 max.
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.
Same engine, lighter car
VO2 max in ml/kg/min is the liters of oxygen your heart and lungs deliver in a minute, times 1,000, divided by your weight in kilograms. Lose 10 percent of your weight with the same heart and the number rises about 11 percent, because 1 divided by 0.9 is 1.11. A 200 lb man in his 40s at 35 is about the 49th percentile. At 180 lb with the same heart he's at 38.9, the 63rd.
That's real: carrying less weight up a hill is easier. But it isn't a stronger engine. Only training raises the liters.
The Dallas five
In 1966, five healthy 20-year-old men were tested for a three-week bed rest study. Retested at 50, their oxygen use had fallen only 11 percent in liters a minute, from 3.3 to 2.9, but 28 percent per kilogram, from 43 to 31, because their weight had risen from 77 to 100 kg. Six months of training brought them back to 3.3 liters a minute, 36 per kilogram.
GLP-1 drugs
On GLP-1 and GLP-1/GIP drugs, about 25 to 40 percent of the weight lost is lean mass, and clinical studies haven't shown a gain in fitness. The number goes up on paper as the weight comes off. Keeping the cardio and lifting twice a week is what makes the engine grow too.
4 sources
- McGuire DK and others, A 30-year follow-up of the Dallas Bedrest and Training Study, part I, Circulation, 2001europepmc.org
- McGuire DK and others, A 30-year follow-up of the Dallas Bedrest and Training Study, part II, Circulation, 2001europepmc.org
- Liu, Weeldreyer and Angadi, GLP-1 drugs, lean mass and cardiorespiratory fitness, 2025pmc.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
