Key takeaways
In a dose-response study, nobody failed to improve at 4 or 5 hours a week, while 69% did not respond to 1 hour
Beginners improve with modest volume at moderate intensity; trained athletes need intervals near VO2max to keep improving
A practical pattern is about 80% easy volume with one or two hard sessions a week, raised gradually
"How much do I need to train?" is the most practical question in endurance fitness, and the evidence gives a clearer answer than most people expect. The short version: dose matters, intensity changes the dose, and what works depends on how fit you already are.
The dose-response study: non-responders respond to more
For years, studies reported that around one in five people following activity guidelines showed no improvement in fitness. Montero and Lundby tested whether this was really about genetics or simply about dose. They split 78 healthy adults into five groups doing one to five 60-minute endurance sessions a week, otherwise following the same 6-week programme.
| Weekly training | Share of non-responders after 6 weeks |
|---|---|
| 60 min (1 session) | 69% |
| 120 min (2 sessions) | 40% |
| 180 min (3 sessions) | 29% |
| 240 min (4 sessions) | 0% |
| 300 min (5 sessions) | 0% |
Then the non-responders did another 6 weeks with two extra sessions a week. Every one of them improved. The authors found that the gain in VO2max was closely tied to the rise in total haemoglobin mass, a blood adaptation. More on individual differences in VO2max trainability.
The takeaway is not that everyone needs five hours a week. It is that if you are not improving, the first fix is usually more training, not a verdict on your genes.
Intensity changes the dose
Volume is only half of the equation. In a review on runners, Midgley, McNaughton and Wilkinson noted that intensities as low as 40 to 50% of VO2max can raise VO2max substantially in untrained people, but that the minimum effective intensity depends heavily on your starting fitness. Well-trained runners probably need to train at high percentages of VO2max, and the authors argued that work at or near VO2max may be the most effective stimulus for them.
Bacon and colleagues pooled interval training studies in a 2013 meta-analysis and found an average VO2max increase of 0.51 litres per minute, with programmes using longer intervals showing gains of roughly 0.8 to 0.9 litres per minute and a marked response in all subjects. That is why sessions like the Norwegian 4×4 are so effective per minute.
Why elite athletes still train mostly easy
If intervals work so well, why not do them every day? Because hard sessions are costly to recover from. Seiler's 2010 review of elite endurance athletes found they converge on roughly 80% of sessions at low intensity and about 20% dominated by high-intensity work such as intervals near 90% of VO2max. Studies that added more high-intensity work to already well-trained athletes did not show convincing long-term gains. Easy volume is the base that lets you absorb the hard work. See 80/20 training.
How the answer changes with fitness level
Midgley, McNaughton and Jones later pointed out that there are relatively few well-controlled training studies in trained distance runners, so recommendations for that group rely partly on physiology and coaching experience. With that caveat, a sensible guide by level looks like this:
| Level | Weekly time | Hard sessions | Running example |
|---|---|---|---|
| Beginner | 2 to 3 hours | 0 to 1, after the first month | 15 to 25 km a week |
| Recreational | 3 to 5 hours | 1 to 2 | 25 to 45 km a week |
| Competitive amateur | 5 to 8 hours | 2 | 45 to 80 km a week |
| Elite | 10+ hours | 2 to 4 | 120 km+ a week |
These are rough ranges, not prescriptions. Cyclists, rowers and swimmers can use the weekly time column instead of distance. For a world-class reference point, Casado and colleagues describe Norwegian-model runners covering around 150 to 180 km a week. See VO2max of elite athletes.
How to progress your training volume
- Start where you are. Count your current weekly time and stay there for two weeks.
- Add time in small steps. Increase weekly volume gradually, and hold or step back every third or fourth week.
- Keep most of it easy. Use the heart rate zone calculator to find your easy range; easy should feel conversational.
- Add one interval session, then a second once the first feels routine. Ideas are in VO2max workouts.
- Retest every 6 to 8 weeks. Use a race or time trial in the VO2max running calculator to see whether the dose is working.
If progress stalls for two test cycles, change one variable at a time: more easy volume first, then interval quality.
Signs you are doing too much
More is better only up to the point you can recover from. Warning signs that the dose has outrun your recovery:
- Resting heart rate creeping up, or heart rate variability trending down for several days.
- Easy runs feeling hard, or heart rate higher than usual at your normal easy pace.
- Interval sessions where you cannot hit targets you managed a week or two earlier.
- Poor sleep, irritability, or niggles that keep coming back.
When these appear, cut volume and intensity for a few days rather than pushing through. Tracking resting heart rate and HRV makes the pattern easier to spot early.
Consistency beats peaks
Gains from training reverse surprisingly quickly once you stop; see how fast you lose VO2max. A moderate plan you can sustain all year beats a big block followed by weeks off. If you need a structured start, the 12-week plan to improve VO2max puts volume and intensity together.
Safety: if you have a heart condition or have been inactive, get medical advice before adding intervals.
Frequently asked questions
How many hours a week to improve VO2max?
For untrained adults, about 2 to 3 hours a week of endurance exercise improves VO2max in most people, and in one study 4 hours a week left nobody unimproved. More trained people need more total time plus regular high-intensity intervals.
How long does it take to improve VO2max?
Measurable gains often appear within 3 to 6 weeks in previously untrained people. Larger gains build over several months as stroke volume and blood volume continue to adapt.
How many km a week should I run to improve VO2max?
There is no single number. Recreational runners often see good gains from roughly 20 to 40 km a week including one or two interval sessions. Elite runners using the Norwegian model run around 150 to 180 km a week, which is far beyond what most people need.
Is volume or intensity more important for VO2max?
Both matter. Intensity gives the biggest gain per minute, especially intervals near VO2max, while volume lets you absorb that work and keep improving. Untrained people respond to either; trained athletes need both.
Sources
- Montero D, Lundby C. Refuting the myth of non-response to exercise training: 'non-responders' do respond to higher dose of training. J Physiol, 2017.
- Midgley AW, McNaughton LR, Wilkinson M. Is there an optimal training intensity for enhancing the maximal oxygen uptake of distance runners? Sports Med, 2006.
- Midgley AW, McNaughton LR, Jones AM. Training to enhance the physiological determinants of long-distance running performance. Sports Med, 2007.
- Bacon AP, Carter RE, Ogle EA, Joyner MJ. VO2max trainability and high intensity interval training in humans: a meta-analysis. PLoS One, 2013.
- Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform, 2010.
- Casado A, Foster C, Bakken M, Tjelta LI. Does lactate-guided threshold interval training within a high-volume low-intensity approach represent the "next step" in the evolution of distance running training? Int J Environ Res Public Health, 2023.