39 FACTORS · RANKED BY RESEARCH
What actually affects your VO2 max?
VO2 max is the single best lab measure of cardiorespiratory fitness, and one of the strongest predictors of how long you'll live. Here's what raises it, what lowers it, and what's just hype, with every claim anchored to research.
Why it matters
n = 122,007
≈5×
higher all-cause mortality for the least-fit vs the fittest, with no upper limit of benefit; low fitness rivals smoking, diabetes, and coronary disease as a risk factor.
Mandsager et al. 2018 · JAMA Network Open · treadmill METs
39
Factors analyzed
40
Peer-reviewed sources
6
Categories of influence
~47
%
Max heritability of trainability
Start here
Levers vs duds.
The short version before you explore all 39. Tap any item to jump to its full card.
Biggest levers
What actually moves the needle most.
HIIT: long interval, high volume
Raises: strongest · Wen et al. 2019
Sprint interval training (SIT)
Raises · Sloth et al. 2013
Body fat / excess weight
Lowers (per-kg) · van Baak et al. 2021
Iron (when deficient)
Raises (if deficient) · Pasricha et al. 2014
Won't raise your ceiling
Popular, but none has been shown to raise VO2 max; several were never tested for it.
Dietary nitrate / beetroot juice
No effect on VO2 max · Gao/Whitlock et al. 2021
Caffeine
No reliable effect · Brietzke et al. 2017
Creatine
Slightly lowers (per-kg) · Gras et al. 2023
Beta-alanine
Not tested for VO2 max · Trexler et al. 2015 (ISSN)
Sodium bicarbonate
Not tested for VO2 max · Hadzic et al. 2019
Vitamin D
No demonstrated effect · Deng et al. 2025
The library
Explore every factor.
Open a category, or filter by direction and evidence strength. Tap any factor to expand its plain-English takeaway, the key study finding, dose, and source.
Direction
Raises
Lowers
No effect
Varies
Predicts outcomes
Evidence
Strong
Moderate–Strong
Moderate
Weak
Showing 39 of 39 factors
Exercise
9
Detraining (stopping training)
Lowers
Strong
Fitness is use-it-or-lose-it. A month off already costs around 4%, and longer layoffs cost more than twice that.
How to Light activity during a layoff blunts the long-term loss
Key finding & study
Meta of 21 athlete studies: VO2 max fell after short-term (≤30 days) cessation (ES −0.62, avg −3.93%) and roughly twice as much after long-term (>30 days) cessation (ES −1.42, avg −9.43%). Higher-trained athletes lost more only in the long-term analysis.
HIIT: long interval, high volume
Raises: strongest
Strong
Hard intervals are the most effective way to raise VO2 max. The version that wins uses longer work bouts (2 min+) and enough total volume, run for at least a month.
How to Work bouts ≥2 min · ≥15 min total interval volume · 4–12 weeks
Key finding & study
Meta of 53 RCTs. vs steady cardio (MICT), only long-interval (≥2 min), high-volume (≥15 min), 4–12 week HIIT beat MICT (SMD 0.65–1.07). Against no training, HIIT overall ran SMD 0.41–1.81, and this long-interval/high-volume subgroup 0.50–2.48.
HIIT: short interval, low volume
Raises
Strong
Short, time-efficient intervals still work well versus doing nothing. They are not clearly better than steady cardio though.
Key finding & study
Even ≤30 s intervals, ≤5 min volume, ≤4 weeks beat no training (SMD 0.79–1.65), but did not clearly beat MICT.
Moderate continuous cardio (MICT)
Raises
Strong
Steady-state cardio works. It is just not as time-efficient as well-structured intervals.
Key finding & study
Reliable VO2 max gains across populations; only beaten by higher-volume HIIT.
Tapering (pre-event)
No VO2 max outcome measured
Strong
Backing off volume before a goal event sheds fatigue so your existing fitness shows up on the day. The evidence is about race performance; this meta-analysis never measured VO2 max at all.
How to ~2-week taper · cut volume 41–60% · keep intensity and frequency
Key finding & study
Meta-analysis of 27 studies. Performance was maximised by a ~2-week taper (ES 0.59 ± 0.33) that exponentially cut training volume by 41–60% (ES 0.72 ± 0.36) while leaving intensity (ES 0.33 ± 0.14) and frequency (ES 0.35 ± 0.17) unchanged. VO2 max was not an outcome in this meta-analysis.
Sprint interval training (SIT)
Raises
Mod–Strong
Very short, very hard sprint sessions reliably raise VO2 max, even with little total work. Great low-time option, but they are genuinely unpleasant.
How to Repeated ~30 s all-out efforts · 2–8 weeks
Key finding & study
Systematic review of 19 studies; 13 pooled for VO2 max: brief all-out sprints (e.g. repeated ~30 s efforts) over 2–8 weeks raised VO2 max versus control (Hedges’ g = 0.63, 95% CI 0.39–0.87), a +4.2 to +13.4% improvement in sedentary and recreationally active adults.
Overtraining / non-functional overreaching
Lowers
Moderate
More is not always better. Pushing past recovery can stall or drop your VO2 max. If your fitness is sliding despite hard training, you may be under-recovered, not under-trained.
Key finding & study
ECSS/ACSM consensus: too much training with too little recovery causes prolonged performance decrements, including reduced VO2 max, that take weeks to months to resolve. This is a narrative expert consensus on overtraining syndrome as a whole, not a pooled analysis of VO2 max.
Resistance training (alone)
Raises (modest, short programs)
Moderate
Lifting gives a modest VO2 max bump in healthy over-60s, and the pooled gain sits in the first six months. This review did not compare it head-to-head against cardio, so it cannot tell you which raises VO2 max more.
How to Programs of ≤24 weeks · evidence is in healthy adults 60+
Key finding & study
Meta-analysis in healthy adults over 60 (37 studies; 24 reported VO2 peak, 22 pooled): resistance training alone raised VO2 peak by 1.89 mL/kg/min (95% CI 1.21–2.57) in programs of 24 weeks or less. Beyond 24 weeks the pooled effect was null (−0.01).
Concurrent training (lifting + cardio)
Neutral (indirect evidence)
Weak
The order you put lifting and cardio in does not change your VO2 max. Whether adding lifting to cardio helps or hurts is a different question, and this evidence does not answer it.
Key finding & study
Meta-analysis of concurrent-training sequence: doing strength work before versus after endurance made no difference to VO2 max (SMD 0.02, p=0.859). Every arm did both types of training; there was no endurance-only comparison, so this does not test whether adding lifting changes VO2 max gains.
Nutrition & Supplements
8
Creatine
Slightly lowers (per-kg)
Strong
Creatine is great for strength and power, and since VO2 max is scored per kg, the number can dip slightly. Added body water and mass is the authors’ likely explanation, not something the trials directly measured.
Key finding & study
Meta of 19 RCTs (n=424): VO2 max rose less with creatine than placebo (ES −0.32, 95% CI −0.51 to −0.12).
Dietary nitrate / beetroot juice
No effect on VO2 max
Strong
Beetroot does not raise your ceiling. It makes a given pace cheaper to hold (better economy), which can help performance without changing VO2 max.
Key finding & study
73 studies (n=1061): nitrate lowered submaximal VO2 (O2 cost) by ~0.04 L/min (p<0.00001) but had no significant effect on VO2 max.
Iron (when deficient)
Raises (if deficient)
Mod–Strong
Fixing low iron raises VO2 max, especially in menstruating women who are prone to deficiency. This is correcting a deficit, not a boost on top of normal iron.
How to Daily iron: only corrects a deficiency, not a boost on top of normal levels
Key finding & study
Meta of 24 RCTs in women of reproductive age; the VO2 max estimate pools 18 of them. Daily iron raised relative VO2 max by 2.35 mL/kg/min (95% CI 0.82–3.88, p=0.003) and lowered submaximal heart rate. Only 3 of the 24 trials were rated at low risk of bias.
Beta-alanine
Not tested for VO2 max
Moderate
Useful for buffering "the burn" in efforts of roughly one to four minutes. There is no evidence it raises VO2 max; the position stand simply does not cover that.
Key finding & study
ISSN position stand: beta-alanine raises intramuscular carnosine and most reliably helps efforts longer than 60 s, with the effect most pronounced in the 1–4 minute range. The position stand does not address VO2 max as an outcome.
Caffeine
No reliable effect
Moderate
Caffeine helps you push harder and feel less effort, which improves performance. It does not raise your VO2 max ceiling; a lot of the benefit is expectation/placebo.
Key finding & study
RCT (n=9): caffeine improved time to exhaustion (~+19%) and peak power (~+13%) but did not change VO2 max, and the gains were matched by a placebo believed to be caffeine.
Omega-3 (fish oil)
Contested for VO2 max
Moderate
Fish oil may make a given effort feel a touch easier and is good for general health. Whether it raises VO2 max is genuinely unsettled: the position stand leans positive, individual trials disagree.
Key finding & study
ISSN position stand. Its own headline conclusion is net-positive for training adaptation and performance, and it reports a lower oxygen cost of submaximal work and lower exercising heart rate. On VO2 max specifically the evidence is contested: some trials show small VO2 peak gains, others are null.
Sodium bicarbonate
Not tested for VO2 max
Moderate
"Baking soda" loading helps some people tolerate the burn in hard efforts, though only about half the trials found any benefit. Its effect on VO2 max has not been tested.
Key finding & study
Systematic review of 35 studies: only 17 reported a performance benefit, concentrated in high-intensity efforts. The review reports no VO2 max outcome. Whether bicarbonate alters the VO2 slow component is contested: Santalla 2003 (7 professional cyclists, 0.3 g/kg) found no change, while Berger 2006 found the slow component delayed.
Vitamin D
No demonstrated effect
Moderate
Worth keeping vitamin D in normal range for general health, but nothing shows it raises VO2 max. The underlying numbers are thin enough that "no effect" is not settled either.
Key finding & study
Network meta-analysis (30 RCTs, 693 athletes) reported no significant VO2 max benefit for vitamin D. The published effect estimates could not be retrieved, so read this as no demonstrated benefit rather than proof of no effect. Deficiency-correction studies are mixed.
Environment
5
Acute altitude (being at altitude)
Lowers (on the spot)
Moderate
The thinner the air, the lower your VO2 max on the spot. Your watch will read lower at elevation until you adapt.
Key finding & study
VO2 max falls roughly 6–8% per 1,000 m of elevation above about 1,500 m; roughly half of that recovers with ~2 weeks of acclimatisation. This is a standard textbook figure from the broader altitude-physiology literature, not a single cited study; treat the percentage as an approximation.
Textbook figure: no single source (cf. Wehrlin 2006)
Air pollution (PM2.5)
Lowers / blunts gains
Moderate
Hard training in heavy traffic or smog works against you. How much depends on exposure in ways this evidence has not pinned down. Favour cleaner air and times of day when you can.
Key finding & study
Systematic review of 24 studies: breathing polluted air during endurance exercise impairs cardiopulmonary responses and can blunt the aerobic-fitness benefit of training. The review did not establish a dose-response relationship between pollutant concentration and the size of the effect.
Altitude (live high, train low)
Raises
Moderate
Sleeping at altitude builds more oxygen-carrying red cells, which can lift VO2 max. The evidence is one small elite study whose controls were a different sport living at low altitude, and the effect is still debated.
How to Sleep high (~2,500 m, 18 h/day), train low · ~3–4 weeks
Key finding & study
Elite orienteers living at 2,500 m (18 h/day) and training lower for 24 days raised hemoglobin mass (805→848 g) and VO2 max (3,515→3,660 mL/min). The unchanged control group were cross-country skiers, and their "sea level" was really 500–1,600 m.
Heat acclimation
Raises
Moderate
Training in the heat expands blood plasma and can nudge VO2 max up, similar in spirit to altitude. The effect is biggest when you are also tested in heat.
How to Repeated heat exposure; effect via plasma-volume expansion
Key finding & study
Meta-analysis pooled four heat-acclimation effects on VO2 max: Hedges’ g = 0.42 overall, 0.63 when tested in the heat, 0.30 versus a control group, and 0.75 versus control when tested in the heat. The +5% cool / +8% hot and ~6.5% plasma-volume figures come from Lorenzo 2010 (12 acclimated cyclists vs 8 controls, tested at 13°C and 38°C).
Waldron et al. 2021 (+ Lorenzo 2010)
Hypoxic training methods
Raises (varies by method)
Moderate
Sleeping high while training low is the most dependable protocol. Doing intervals in a hypoxic mask is the weakest version, and the newest meta-analysis finds it does not work at all.
How to Live-high/train-low ranks most reliable; hypoxic-mask intervals do not
Key finding & study
Bayesian network meta-analysis (59 studies) ranked live-high/train-low combined with low-altitude training best (P-scores 0.92 and 0.86); intermittent hypoxic training ranked far lower (0.37) and intermittent hypoxic exposure at rest lowest (0.07). A 2025 meta-analysis of 35 studies contradicts this row for intermittent hypoxic training specifically: no VO2 max benefit over normoxic training (p=0.333), with evidence of publication bias.
Feng et al. 2023 (vs Dorelli et al. 2025)
Demographics & Physiology
7
Age
Lowers
Strong
VO2 max drops with age, and the drop speeds up sharply in later decades. Single snapshots across ages make aging look gentler than it really is.
Key finding & study
Baltimore Longitudinal Study (n=810, ages 21–87): peak VO2 decline accelerates each decade rather than being linear: roughly 3–6% per decade through the 20s and 30s, rising to more than 20% per decade from the 70s onward. The decline is faster in men from the 40s onward.
Body fat / excess weight
Lowers (per-kg)
Strong
Because the score is "per kilo," losing fat raises your VO2 max number even if your heart and lungs do not change. The 3.82 figure above is what training delivered in these trials.
How to Training + fat loss; the score is per kg of body weight
Key finding & study
VO2 max is expressed per kg, so carrying more fat lowers the number. In adults with overweight/obesity, training raised relative VO2 max by 3.82 mL/kg/min (66 RCTs, n=3,964); that figure is the effect of the training programmes, not of fat loss on its own.
Genetics (trainability)
Varies by person
Strong
How much your VO2 max improves from the same training is heavily genetic: up to roughly half of the response. Some people are high responders, some barely move. It runs in families.
Key finding & study
HERITAGE Family Study (n=481, 20-wk identical training): mean gain ~400 mL/min but ranged from no gain to >1.0 L/min. Maximal heritability of the training response was estimated at ~47% (an upper bound, in a Caucasian family sample).
Bouchard et al. 1999 (HERITAGE)
Dehydration / hypohydration
Lowers
Moderate
Showing up dehydrated lowers your VO2 max on the day because there is less blood volume to pump. Hot conditions make it worse.
How to Avoid >2% body-mass water loss before testing or hard efforts
Key finding & study
Review: losing more than ~2% of body mass as water lowers maximal aerobic capacity, mainly by shrinking plasma volume (lower stroke volume and cardiac output). The impairment compounds in the heat.
Immobilization / bed rest
Lowers (severe)
Moderate
Extended inactivity is brutally fast at erasing fitness. Three weeks flat on your back cost these men about as much VO2 max as four decades of aging (from a five-man study, so hold the exact number loosely).
Key finding & study
Dallas Bed Rest Study (5 men): 3 weeks of strict bed rest cut VO2 max ~26%, reversed by 8 weeks of training. The 40-year follow-up found 40 years of aging cost ~27%, a comparable drop. Five men, no control group; the usual "falling cardiac output" explanation is not established by this study.
Sex
Varies
Moderate
Men average higher VO2 max largely because they carry more oxygen per unit of blood and have bigger hearts. The ~10% figure is elite-versus-elite, per kilogram of body weight.
Key finding & study
Narrative review: a ~10–12% endurance performance gap. Comparing elite men with elite women, male VO2 max averages ~10% higher per kg of body mass, driven mainly by greater oxygen delivery (higher hemoglobin mass, larger heart). The review gives no per-fat-free-mass figure.
Blood donation (acute)
No clear reduction
Weak
Losing ~500 mL of blood sounds like it should dent your VO2 max, but the pooled evidence does not show a significant drop. The review is small and individual studies disagree, so do not plan around a large effect in either direction.
Key finding & study
Systematic review of whole-blood donation (~500 mL): the change in VO2 max was not statistically significant, and the review concludes VO2 max is not reduced by donation. Submaximal responses do shift. The stroke-volume / cardiac-output explanation does not come from this review.
Lifestyle
6
Alcohol (previous-day)
Lowers (performance)
Moderate
Drinking the night before a hard session measurably hurts endurance the next day. The hit is to how long you can hold an effort, more than to your VO2 max ceiling.
Key finding & study
RCT (n=12): a previous-evening alcohol dose (1.09 g ethanol per kg fat-free mass) cut next-morning cycling time to exhaustion by ~11% (181 vs 203 s); strength tests were unaffected. The effect is on endurance capacity rather than a proven VO2 max change.
Cold-water immersion (post-training)
No VO2 max estimate
Moderate
Ice baths clearly cost you strength gains. For VO2 max there is no pooled evidence either way; this meta-analysis simply did not produce that number.
Key finding & study
Meta-analysis: routinely ice-bathing after sessions blunts strength and power gains (SMD −0.60). It reports no pooled VO2 max estimate, so it neither confirms nor rules out an effect on aerobic capacity.
Sauna bathing (habitual)
Raises
Moderate
More frequent sauna sessions track with higher fitness in Finnish men; how long you sit does not. The cohort is observational, and the one supporting trial is from the same authors.
How to Frequency, not duration: 2–3 or more sessions per week
Key finding & study
Kuopio cohort of 2,012 men aged 42–61: versus one session a week, 2–3 sessions/week were associated with +0.84 mL/kg/min (p=.008) and 4–7 sessions/week with +1.17 mL/kg/min (p=.041) of estimated fitness; at 11 years only the 2–3/week group remained significant (+1.22, p=.038). Session duration was not associated with fitness. The ~+2.7 mL/kg/min post-exercise-sauna figure comes from a small RCT by the same group, not an independent trial.
Sedentary behavior (sitting time)
Lowers
Moderate
Long sitting days track with lower fitness, mainly in people who are not otherwise very active. If you already train a lot, this study does not show sitting hurting you.
Key finding & study
In 16,025 adults, more daily sitting was associated with lower estimated cardiorespiratory fitness, but no association was seen among the most physically active participants, so it is not independent of exercise. Fitness was estimated, not measured directly.
Sleep deprivation
Lowers (performance)
Moderate
A bad night clearly hurts how long and how hard you can go. What it does to your VO2 max number specifically has not been tested here.
Key finding & study
Meta-analysis of 45 studies, 16 of them on aerobic endurance: sleep deprivation cut aerobic endurance performance (SMD −0.76, 95% CI −1.27 to −0.25; athletes −0.66, non-athletes −1.02) and raised perceived exertion. This paper reports no VO2 max outcome; claims that acute sleep loss spares VO2 max, or that chronic short sleep lowers it, are not supported by this source.
Smoking
Lowers
Moderate
Smokers in this study had a measurably lower aerobic ceiling. Because it is a single cross-sectional snapshot, it cannot tell you whether quitting restores it.
Key finding & study
Cross-sectional study (n=70, step-test estimate): current smokers had lower estimated VO2 max (38.8) than never-smokers (41.6) and former smokers (41.4). The carbon-monoxide-binds-hemoglobin explanation is standard physiology, not something this study measured. The authors disclose tobacco-industry-funded research ties.
Clinical
4
Heart failure (VO2 max as prognosis)
Lowers (prognostic)
Strong
The heart can’t deliver enough oxygen, so VO2 max falls and is one of the strongest predictors of survival in heart failure. The classic ≤14 figure is a transplant-timing threshold, not the worst-prognosis group in the original data.
Key finding & study
Landmark CPET study: peak VO2 ≤14 mL/kg/min became the heart-transplant timing threshold, though that group still had ~70% one-year survival. The worst prognosis belonged to patients rejected from transplant for noncardiac reasons: 47% one-year and 32% two-year survival.
Low fitness as a mortality risk factor
Predicts mortality
Strong
Low fitness is one of the strongest markers of dying early, on par with major disease risk factors, and there’s no point of diminishing returns. This is exercise-test fitness in METs rather than a lab VO2 max.
Key finding & study
In 122,007 adults followed ~8.4 years, higher treadmill-derived cardiorespiratory fitness (measured in METs, not laboratory VO2 max) was associated with lower all-cause mortality with no upper limit of benefit; the least-fit had ~5× the adjusted mortality risk of the fittest. Observational, so this is an association rather than proof that raising fitness lowers risk.
Long COVID
Lowers
Moderate
Lingering COVID symptoms come with a measurably lower VO2 max. Certainty is low and the studies lean toward people who were hospitalised, so milder cases may be less affected.
Key finding & study
Meta-analysis (9 studies, 464 symptomatic vs 359): peak VO2 was 4.9 mL/kg/min lower in people with ongoing symptoms 3+ months after infection, at low certainty of evidence. The included cohorts oversampled people who had been hospitalised, so the gap may be smaller after milder infection.
Type 2 diabetes
Lowers
Moderate
Type 2 diabetes meaningfully lowers aerobic fitness, and low fitness in turn predicts worse outcomes. Exercise that raises VO2 max is one of the highest-value interventions here.
Key finding & study
Meta-analysis (77 studies): people with type 2 diabetes averaged 5.84 mL/kg/min lower VO2 max than those without, driven by cardiac, microvascular, and mitochondrial impairments.
FAQ
Reset
Showing 10 of 39 factors
1
3
1
Showing 26 of 39 factors
2
Showing 36 of 39 factors
Showing 38 of 39 factors
Showing 12 of 39 factors
Showing 14 of 39 factors
Showing 37 of 39 factors
Common questions.
What raises VO2 max the most?
Training is the biggest lever: high-intensity interval training raises VO2 max most, and only long-interval (2 min+), high-volume HIIT clearly beats steady cardio (SMD 0.65–1.07 across 53 RCTs). Sprint intervals follow (Hedges g 0.63), then moderate continuous cardio. Because VO2 max is measured per kilogram, training in people carrying excess weight raises the number further, and correcting iron deficiency helps in people who are low on iron.
Do supplements like beetroot, caffeine, or creatine increase VO2 max?
No supplement in this library has been shown to raise VO2 max. Dietary nitrate (beetroot) improves exercise economy but has no significant effect on the VO2 max ceiling; caffeine is ergogenic mostly via lower perceived effort; and creatine can slightly lower the per-kilogram number because it adds water weight. Beta-alanine and sodium bicarbonate help short hard efforts but were never tested for VO2 max, vitamin D showed no demonstrated benefit in athletes, and the omega-3 evidence is contested rather than clearly null.
What lowers VO2 max?
Stopping training (detraining), overtraining without recovery, aging, excess body fat, bed rest or immobilization, dehydration, acute altitude above about 1,500 m, air pollution, smoking, long COVID, and type 2 diabetes all lower VO2 max. Previous-day alcohol, sleep deprivation, and prolonged sitting hurt endurance performance or track with lower fitness, but were not shown to lower measured VO2 max itself. Blood donation is a common assumption that the pooled evidence does not support.
Why does VO2 max matter for health?
In a study of 122,007 adults, the least-fit people had roughly five times the all-cause mortality risk of the fittest, with no upper limit of benefit. Low cardiorespiratory fitness, measured as treadmill METs rather than a laboratory VO2 max, was a risk factor comparable to or greater than smoking, diabetes, or coronary artery disease. The study is observational, so this is a strong association rather than proof of cause.
How much of VO2 max trainability is genetic?
Up to about 47%. In the HERITAGE Family Study, identical 20-week training produced gains ranging from none to over 1 litre per minute, and the maximal heritability estimate for that response was ~47% (an upper bound, in a Caucasian family sample). Trainability clearly runs in families.
Keep exploring
Related tools.
More free, evidence-based tools to get the most out of your wearable.
Accuracy vs lab CPET
Garmin
Apple
Polar
Fitbit
Most Accurate VO2 Max Wearable
How accurately do wearables estimate VO2 max vs a lab CPET? 9 devices compared.
Wearables · 13 sources
Open
Readiness score
↑ Validated
Recovery Score Explorer
Compare readiness and recovery scores across 12 wearables, and see which are actually validated.
Recovery · 12 wearables
Open
HRV, beat-to-beat
HRV Factor Explorer
43 research-backed factors that affect Heart Rate Variability, ranked by evidence.
Recovery · 43 factors
Open
Related Tool
Pair it with
Most Accurate VO2 Max Wearable
See how 9 watches & rings actually stack up against a lab CPET: which brands are independently validated, and which overestimate.
Sources
Every factor, anchored.
Each factor is tied to a primary source, opened and checked against the record (PubMed / PMC / journal).
Exercise: HIIT/MICT
Wen et al. 2019: HIIT protocols for VO2 max
J Sci Med Sport. 2019;22(8):941-947.
Nutrition: nitrate
Gao/Whitlock et al. 2021: Dietary nitrate
J Int Soc Sports Nutr. 2021;18:55.
Physiology: age
Fleg et al. 2005: Aerobic capacity decline with age
Circulation. 2005;112(5):674-682.
Physiology: genetics
Bouchard et al. 1999: HERITAGE Family Study
J Appl Physiol. 1999;87(3):1003-1008.
Physiology: sex
Santisteban et al. 2022: Sex differences in VO2 max
Int J Environ Res Public Health. 2022;19(9):4946.
Nutrition: iron
Pasricha et al. 2014: Iron & physical performance
J Nutr. 2014;144(6):906-914.
Environment: altitude
Wehrlin et al. 2006: Live high, train low
J Appl Physiol. 2006;100(6):1938-1945.
Exercise: detraining
Zheng et al. 2022: Detraining & VO2 max
BioMed Research Int. 2022;2022:2130993.
Nutrition: caffeine
Brietzke et al. 2017: Caffeine & VO2 max
Nutrition and Health. 2017;23(4):231-238.
Physiology: body fat
van Baak et al. 2021: Exercise & fitness in obesity
Obesity Reviews. 2021;22(S4):e13239.
Physiology: bed rest
Saltin et al. 1968: Dallas Bed Rest Study
Circulation. 1968;38(5 Suppl):VII1-78.
Environment: heat
Waldron et al. 2021: Heat acclimation & VO2 max
Sports Medicine. 2021;51(7):1509-1525.
Nutrition: creatine
Gras et al. 2023: Creatine & VO2 max
Crit Rev Food Sci Nutr. 2023;63(21):4855-4866.
Nutrition: beta-alanine
Trexler et al. 2015, ISSN position stand: Beta-Alanine
J Int Soc Sports Nutr. 2015;12:30.
Lifestyle: smoking
Caci et al. 2024: Smoking & aerobic capacity
Intern Emerg Med. 2024.
Physiology: blood donation
Johnson et al. 2019: Whole-blood donation & exercise
PLOS ONE. 2019;14(4):e0215346.
Clinical: long COVID
Durstenfeld et al. 2022: CPET in long COVID
JAMA Netw Open. 2022;5(10):e2236057.
Nutrition: bicarbonate
Hadzic et al. 2019: Sodium bicarbonate
J Sports Sci Med. 2019;18(2):271-281.
Nutrition: vitamin D
Deng et al. 2025: Supplements & VO2 max (network meta-analysis)
Food Sci Nutr. 2025.
Exercise: overtraining
Meeusen et al. 2013: Overtraining syndrome consensus
Eur J Sport Sci. 2013;13(1):1-24 (also Med Sci Sports Exerc. 2013;45:186-205).
Clinical: heart failure
Mancini et al. 1991: Peak VO2 & transplant timing
Circulation. 1991;83(3):778-786.
Clinical: type 2 diabetes
Macedo et al. 2023: VO2 max in type 2 diabetes
Arch Endocrinol Metab. 2023.
Nutrition: omega-3
Jäger et al. 2024, ISSN position stand: Omega-3
J Int Soc Sports Nutr. 2024;22(1).
Lifestyle: alcohol
Shaw et al. 2022: Previous-day alcohol & performance
Int J Sports Physiol Perform. 2022;17(1):44-50.
Physiology: dehydration
Cheuvront & Sawka 2010: Hydration & performance
J Appl Physiol. 2010;109(6):1989-1995.
Exercise: SIT
Sloth et al. 2013: Sprint interval training
Scand J Med Sci Sports. 2013;23(6):e341-352.
Exercise: resistance
Smart et al. 2022: Resistance training & VO2 peak
Age Ageing. 2022;51(6):afac143.
Environment: air pollution
González-Rojas et al. 2025: Air pollution & exercise
Life. 2025;15(4):595.
Lifestyle: sleep
Kong et al. 2025: Sleep deprivation & performance
Front Physiol. 2025.
Lifestyle: sauna
Kunutsor et al. 2024: Sauna & cardiorespiratory fitness
J Cardiopulm Rehabil Prev. 2024;44(4):295-300.
Exercise: tapering
Bosquet et al. 2007: Tapering & performance
Med Sci Sports Exerc. 2007;39(8):1358-1365.
Exercise: concurrent
Gao & Yu 2023: Concurrent training sequence
Front Physiol. 2023;14:1072679.
Environment: hypoxia
Feng et al. 2023: Hypoxic training methods
Front Physiol. 2023;14:1223037.
Lifestyle: sedentary
Eriksen et al. 2016: Sitting time & fitness
Scand J Med Sci Sports. 2016;26(12):1435-1443.
Lifestyle: cold-water
Malta et al. 2021: Cold-water immersion & adaptation
Sports Medicine. 2021.
Why it matters
Mandsager et al. 2018: Fitness & long-term mortality
JAMA Network Open. 2018;1(6):e183605.
Nutrition: bicarbonate
Santalla et al. 2003: Bicarbonate & the VO2 slow component
J Sports Sci. 2003;21(1):39-47.
Nutrition: bicarbonate
Berger et al. 2006: Bicarbonate alters the slow phase of VO2 kinetics
Med Sci Sports Exerc. 2006;38(11):1909-1917.
Environment: heat
Lorenzo et al. 2010: Heat acclimation improves exercise performance
J Appl Physiol. 2010;109(4):1140-1147.
Environment: hypoxia
Dorelli et al. 2025: Aerobic intermittent hypoxic training is not beneficial
Scand J Med Sci Sports. 2025;35:e70088.
Show all 40 sources
From the blog
Show fewer sources
Keep reading.
The long-form, evidence-based articles behind this tool.
Wearables & Data
What Affects VO2 Max? The Levers That Work (and the Ones That Waste Your Time)
Training raises VO2 max. Most supplements do not. Every factor that moves the number, ranked by evidence strength.
9 min read
Read
Wearables & Data
Most Accurate VO2 Max Wearable: Garmin, Apple, WHOOP & Oura Ranked
No wearable measures VO2 max. They estimate it, and the gap between brands is large. Which device the research actually backs.
8 min read
Read
HRV & Recovery
How to Improve HRV: 44 Factors Ranked by Evidence (2026)
Forty-four factors that affect heart rate variability, ranked by how strong the peer-reviewed evidence really is.
12 min read
Read
This content is for informational purposes only and is not medical advice. Always consult a qualified healthcare provider before making health or training decisions.
Anchored to peer-reviewed research, each source verified against the primary record. Last updated August 2026.