The short answer
How fast your fitness can improve
Training studies show measurable changes in VO2max within weeks, not months:
| Training | Time | VO2max change |
|---|---|---|
| Kettlebell snatch intervals, 3 times a week | 4 weeks | Up about 6% 1 |
| Tabata intervals, 5 days a week | 6 weeks | Up 7 ml/kg/min 2 |
| 4 x 4 minute running intervals, 3 times a week | 8 weeks | Up 7.2% 3 |
| Steady cycling or intervals, people new to training | 8 weeks | Up about 18% 4 |
Two things make the gains bigger. People who start less fit improve more, and longer programs produce larger gains than short ones5. So if you are new to training, expect your first few tests to climb quickly; if you are already fit, expect smaller steps.
How fast it can drop
Fitness fades faster than it builds. In a study of trained endurance athletes who stopped training completely, VO2max fell 7% in the first three weeks. It kept falling to about 16% below where it started by eight weeks, then leveled off, still above people who had never trained6.
The drop is steepest in highly trained athletes and gentler in people who only recently got fit7. Either way, a few weeks off is enough to show up on your next test.
How much a single test can vary
When 60 young adults ran the 12-minute test three separate times, the test proved reliable overall. The biggest source of error was how each person happened to perform on a given day8. Sleep, fatigue, heat, wind and pacing all move the number a little.
The same study found the VO2max estimate tends to read low for less fit people and high for very fit people8. That makes the test better for comparing yourself with yourself over time than for comparing yourself with a lab result.
So how often should you test?
| Situation | When to test |
|---|---|
| Starting out | Once to get your baseline, then again after 6 to 8 weeks of training. |
| During a training block | At the start and end of each 6 to 8 week block. Our VO2max Engine program tests in Week 1 and Week 8. |
| After 3 or more weeks off | Retest before you train again, so your new starting point is accurate. |
| Wanting to test sooner | Wait at least 4 weeks. Sooner than that, a real change is hard to tell apart from a good or bad day, and each test costs you a hard session. |
Make every test comparable
- Use the same route or track, and the same way of measuring: GPS and lap counting can differ by a few percent.
- Test at the same time of day, after the same warm-up.
- Come in rested: no hard training the day before.
- Avoid unusual heat or strong wind, or note it when you save the result.
- Pace evenly. Starting too fast is the most common way to run a worse test than your fitness deserves.
Try this workout
The Cooper test, the same way every time
Who it is for: Anyone tracking their aerobic fitness, every 6 to 8 weeks.
- 1The day before. No hard training.
- 2Set up. Same route or track, same time of day, same warm-up as last time.
- 3The test. Run as far as you can in 12 minutes at an even pace. Starting too fast is the most common way to run a worse test than your fitness deserves.
- 4Record it. Save the distance and note any heat or wind. Judge progress by the trend across two or three tests: how you happened to perform on the day was the biggest source of error 8.
Want it planned week by week? VO2max Engine builds on this session.
Put it into practice
Sources
All research- 1Effects of kettlebell training on aerobic capacityFalatic et al., 2015. Journal of Strength and Conditioning Research 29(7):1943-1947.
- 2Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2maxTabata et al., 1996. Medicine & Science in Sports & Exercise 28(10):1327-1330.
- 3Aerobic high-intensity intervals improve VO2max more than moderate trainingHelgerud et al., 2007. Medicine & Science in Sports & Exercise 39(4):665-671.
- 4The effects of high intensity interval training vs steady state training on aerobic and anaerobic capacityFoster et al., 2015. Journal of Sports Science and Medicine 14(4):747-755.
- 5Effectiveness of high-intensity interval training (HIT) and continuous endurance training for VO2max improvements: a systematic review and meta-analysis of controlled trialsMilanović et al., 2015. Sports Medicine 45(10):1469-1481.
- 6Time course of loss of adaptations after stopping prolonged intense endurance trainingCoyle et al., 1984. Journal of Applied Physiology 57(6):1857-1864.
- 7Detraining: loss of training-induced physiological and performance adaptations. Part I: short term insufficient training stimulusMujika and Padilla, 2000. Sports Medicine 30(2):79-87.
- 8Validity and reliability analysis of Cooper's 12-minute run and the multistage shuttle run in healthy adultsPenry et al., 2011. Journal of Strength and Conditioning Research 25(3):597-605.
General fitness information, not medical advice. If you have an injury or a health condition, check with a professional before starting a new kind of training.