Key takeaways
VO2max is measured per kilogram, so gaining 5 kg can drop it from 62 to 58 with no change in your heart
At around 77 kg, each kilo is worth about 0.8 ml/kg/min of relative VO2max
Daily swings of 1 to 3 kg are mostly water and food, so judge weight and VO2max trends over weeks
VO2max is usually given relative to body weight (ml/kg/min). Behind it sits an absolute number: the litres of oxygen your body can use per minute, which mostly reflects the size and pumping capacity of your heart and the oxygen-carrying capacity of your blood.
relative VO2max = absolute VO2max (ml/min) ÷ body weight (kg)
The maths with real numbers
A runner at 77 kg with a VO2max of 62 uses about 4.8 litres of oxygen per minute at maximum (62 × 77 = 4,774 ml). At 82 kg, the same 4.8 litres works out to about 58 ml/kg/min. Nothing changed in the engine; there is more to carry.
| Weight | Same engine (4.8 L/min) → VO2max |
|---|---|
| 75 kg | 64 |
| 77 kg | 62 |
| 80 kg | 60 |
| 82 kg | 58 |
Roughly: each kilo is worth about 0.8 ml/kg/min at this size.
What it feels like
- At a fixed treadmill speed, heart rate runs a few beats higher and sessions feel harder.
- Hills and stairs are hit hardest, because you lift the extra weight against gravity.
- Your watch's estimate may dip, since it uses your pace for a given heart rate and your entered weight.
Water and food are not fitness
Day-to-day swings of 1–3 kg are mostly water, glycogen and food in the gut — after a big meal, a salty dinner or a heavy training day. They disappear within days. Judge trends over weeks, not single weigh-ins.
Muscle vs fat
Not every kilo is equal. Muscle in the legs and trunk can make you faster, stronger and more robust even if it lowers relative VO2max a little. That matters in mixed sports like Hyrox, where you push sleds and carry weights, and it is why strength training belongs in most plans. Fat that doesn't do work is pure cost on the run.
The takeaway
- For races where you carry your body, being lean (not light at any cost) on race day matters as much as weeks of training.
- If your VO2max drops after a weight gain, check the absolute number before deciding you lost fitness.
- Eat enough to train well: under-fuelling lowers training quality and raises injury and illness risk.
Related: What is VO2max? · How accurate is your watch's VO2max?
Frequently asked questions
Does weight affect VO2max?
Yes. VO2max is usually given per kilogram, so the same heart and blood spread over more body weight gives a lower number. A 77 kg runner at 62 ml/kg/min would read about 58 at 82 kg.
Does losing weight increase VO2max?
Losing excess fat raises relative VO2max even if your absolute oxygen uptake does not change, because you have less weight to carry. Eat enough to train well, since under-fuelling lowers training quality.
What is the difference between absolute and relative VO2max?
Absolute VO2max is the litres of oxygen your body can use per minute. Relative VO2max divides that by body weight, giving ml/kg/min, the figure watches and charts usually show.
Sources
- Bassett DR, Howley ET. Limiting factors for maximum oxygen uptake and determinants of endurance performance. Med Sci Sports Exerc, 2000.