Key takeaways
VO2max is your aerobic ceiling, while lactate threshold and FTP show how much of that ceiling you can hold for long
Max heart rate and SpO2 are not fitness measures, and HRV tracks recovery rather than capacity
Endurance performance depends on three things together: VO2max, threshold as a share of VO2max, and economy
Fitness apps throw a lot of numbers at you: VO2max, lactate threshold, FTP, HRV, max heart rate, even blood oxygen. They measure different things, and mixing them up leads to bad training decisions. Here's what each one tells you.
The big picture
Joyner and Coyle (2008) described endurance performance as the product of three factors: VO2max (the size of the engine), lactate threshold (how much of it you can use for a long time), and economy (how much speed or power you get per litre of oxygen). Bassett and Howley (2000) reached a similar conclusion: VO2max sets the upper limit, but threshold and economy decide who wins among athletes with similar values.
Comparison table
| Metric | What it measures | Units | How to test | How to train |
|---|---|---|---|---|
| VO2max | Maximal oxygen uptake: the aerobic ceiling | ml/kg/min | Lab ramp test with gas analysis; field or watch estimates | Intervals at 90–95% HRmax, aerobic volume |
| VO2peak | Highest oxygen uptake reached in a given test | ml/kg/min | Same as VO2max, without a confirmed plateau | Same as VO2max |
| Lactate threshold | Intensity where blood lactate starts rising fast | Pace, watts, heart rate, % VO2max | Blood lactate step test; 30-min time trial | Threshold intervals, high easy volume |
| FTP | Power sustainable for about an hour | Watts, W/kg | 20-min test × 0.95, or ramp test | Sweet-spot and threshold intervals |
| HRV | Beat-to-beat variation in heart rhythm | ms (usually RMSSD) | Morning or overnight readings, compared with your baseline | Not trained directly: sleep, recovery, fitness |
| Max heart rate | Highest heart rate you can reach | Beats per minute | All-out field test; formula as a rough guide | Hardly trainable |
| Anaerobic capacity | Energy from non-oxygen systems in short efforts | Watts, seconds, sprint times | 30-s all-out test; 1–2 min efforts | Sprint and short all-out intervals |
| SpO2 | Share of haemoglobin carrying oxygen | % | Pulse oximeter or watch | Not trainable; a health signal |
VO2max vs lactate threshold
VO2max is the most oxygen your body can use. Lactate threshold is the effort at which lactate accumulates faster than it's cleared. Joyner and Coyle note that blood lactate starts rising at about 60% of VO2max in untrained people but 75–90% in trained athletes. That's why two runners with the same VO2max can race very differently: a marathon is run at roughly 75–85% of VO2max, a 10 km at 90–100%, and a 5 km close to VO2max.
VO2max responds best to hard intervals; threshold responds to volume and sustained efforts just below it. Most plans use both (see 80/20 training).
VO2max vs threshold: which matters more?
For events over about 15 minutes, threshold usually predicts performance better, as Bassett and Howley noted for distance runners. But threshold is a percentage of VO2max, so a low ceiling caps it. Beginners gain both from almost any training; trained athletes need targeted work for each.
VO2max vs VO2peak
Strictly, VO2max requires a plateau: oxygen uptake stops rising even though the workload does. Many people, especially beginners and patients, stop before that plateau, so the highest value is called VO2peak. Poole and Jones (2017) argued that labs should confirm true VO2max with a short verification test after the ramp. More in VO2max tests explained.
VO2max vs FTP
FTP (functional threshold power) is a cyclist's best power for about an hour, often estimated as 95% of a 20-minute test. It sits near lactate threshold: Valenzuela et al. (2018) found FTP and lactate threshold power similar in trained cyclists, though FTP was lower in recreational riders. Power at VO2max is clearly higher and can be held for only a few minutes. Use the VO2max calculator to estimate VO2max, and see VO2max for cycling for how both feed into bike training.
VO2max vs HRV
HRV (heart rate variability) reflects how your autonomic nervous system is responding to training, stress and sleep. Plews et al. (2013) showed that tracking HRV trends helps elite endurance athletes judge whether they're adapting or overreaching. Fitter people tend to have higher HRV, but day-to-day HRV says nothing about your ceiling; it tells you whether today is a good day to go hard. See resting heart rate, HRV and recovery.
VO2max vs max heart rate
VO2max = cardiac output × oxygen extraction, and cardiac output = heart rate × stroke volume. Training raises stroke volume, not max heart rate, which falls slowly with age. Tanaka et al. (2001) found max heart rate is best predicted as 208 − 0.7 × age, with a standard deviation of about 10 beats per minute. A high max heart rate isn't a sign of fitness; it's useful mainly for setting zones with the heart rate zone calculator.
VO2max vs anaerobic capacity
Anaerobic capacity powers short all-out efforts lasting up to about 2 minutes. Even in 5 and 10 km races, Joyner and Coyle estimate anaerobic metabolism supplies only about 10–20% of energy. "Anaerobic threshold" is an older name for lactate or ventilatory threshold, not a separate measure.
VO2max vs SpO2
SpO2 is the percentage of haemoglobin carrying oxygen, normally about 95–100% at sea level. It stays high in fit and unfit healthy people alike, so it isn't a fitness metric. Low readings at rest can signal illness or high altitude (see altitude training and VO2max).
For background, read what is VO2max and what limits VO2max. Runners can turn a race time into a VO2max estimate with the VO2max running calculator.
Safety: maximal tests and threshold tests are hard efforts. If you have heart disease, high blood pressure, or symptoms such as chest pain or unusual breathlessness, get medical advice first. A low SpO2 reading at rest with symptoms needs medical attention.
Frequently asked questions
What is the difference between VO2 max and lactate threshold?
VO2max is the most oxygen your body can use per minute at maximal effort. Lactate threshold is the intensity above which lactate builds up quickly, often about 60% of VO2max in untrained people and 75 to 90% in trained athletes.
Is FTP the same as VO2 max?
No. FTP is the power a cyclist can hold for about an hour, close to threshold. Power at VO2max is clearly higher, and you can hold it for only a few minutes.
What is the difference between VO2 max and VO2 peak?
VO2max is a true plateau in oxygen uptake despite rising effort. VO2peak is simply the highest value reached in a test, which may fall short of the true maximum if the test ended early.
Does a higher max heart rate mean a higher VO2 max?
No. Max heart rate depends mostly on age and genetics and barely changes with training. Fitness raises stroke volume, the blood pumped per beat, not the top heart rate.
Sources
- Joyner MJ, Coyle EF. Endurance exercise performance: the physiology of champions. J Physiol, 2008.
- Bassett DR, Howley ET. Limiting factors for maximum oxygen uptake and determinants of endurance performance. Med Sci Sports Exerc, 2000.
- Poole DC, Jones AM. Measurement of the maximum oxygen uptake VO2max: VO2peak is no longer acceptable. J Appl Physiol, 2017.
- Valenzuela PL, et al. Is the functional threshold power a valid surrogate of the lactate threshold? Int J Sports Physiol Perform, 2018.
- Plews DJ, et al. Training adaptation and heart rate variability in elite endurance athletes: opening the door to effective monitoring. Sports Med, 2013.
- Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. J Am Coll Cardiol, 2001.