Key takeaways
Women's VO2max averages roughly 10–20% below men's of the same age and training, mainly due to lower haemoglobin and smaller hearts
On average, menstrual cycle phase has only a trivial effect on performance, so train by how you feel
Regular hard training slows the post-menopause decline and keeps women fitter than sedentary peers for decades
Most VO2max research was historically done on men, and women were often told to apply the results with a shrug. That has changed. We now know a lot more about how female physiology shapes aerobic fitness across the lifespan — and the main message is reassuring: women respond to training just as well as men do.
Why women's VO2max is lower on average
At the same age and training status, women's VO2max is typically around 10–20% lower than men's in ml/kg/min. The gap is not about effort or trainability. It comes mostly from oxygen delivery (see what limits VO2max):
- Haemoglobin: women have lower haemoglobin concentration and total haemoglobin mass, so each litre of blood carries less oxygen.
- Heart size: women have smaller hearts and lower stroke volume on average, even relative to body size.
- Body composition: a higher essential fat percentage lowers VO2max when expressed per kilogram (see VO2max and body weight).
- Lung size: smaller airways and lungs matter mostly in highly trained women at very high workloads.
This is why the VO2max norms and the VO2max chart are split by sex. Compare yourself with women of your age, not with men's tables.
The menstrual cycle
Oestrogen and progesterone rise and fall across the cycle and affect body temperature, breathing, fluid balance and fuel use. It seemed logical that performance would swing too. McNulty and colleagues pooled the available studies in a 2020 meta-analysis and found that, on average, performance may be trivially reduced in the early follicular phase (around menstruation) compared with other phases. The effect was small and the evidence quality low.
What that means in practice:
- There is no need to plan training rigidly around the cycle. Your VO2max does not meaningfully change week to week.
- Individual experience matters. Cramps, heavy bleeding, poor sleep or headaches can make a hard session miserable. Moving a 4×4 interval session by a day or two costs nothing.
- Heart rate and temperature run slightly higher after ovulation, which can make watch estimates and easy-pace heart rate drift. Track resting heart rate and HRV over months, not days.
- Missing periods is a warning sign, not a sign of fitness. It often signals low energy availability (REDs), which harms bone health and performance. See a doctor.
Heavy periods are also a common cause of iron deficiency, which lowers endurance performance. If you feel unusually tired, ask for a blood test that includes ferritin.
Pregnancy
Pregnancy changes the cardiovascular system dramatically: blood volume and cardiac output rise, resting heart rate climbs and breathing increases. The American College of Obstetricians and Gynecologists (ACOG) and the Canadian guideline both recommend that women with uncomplicated pregnancies stay active, aiming for roughly 150 minutes of moderate activity a week.
| Stage | General guidance |
|---|---|
| Before conception | Build fitness; regular training is linked to fewer complications |
| First trimester | Continue usual training if well; manage fatigue and nausea |
| Second and third trimester | Lower intensity; use the talk test rather than heart rate; avoid lying flat for long |
| Postpartum | Return gradually; pelvic floor rehab first; speak to your doctor about timing |
Women who were already very active can usually continue more vigorous training with their care team's agreement. Avoid contact sports, activities with a high fall risk, and overheating.
Safety: stop and seek medical advice if you notice bleeding, fluid leakage, chest pain, dizziness, regular painful contractions or calf swelling.
Menopause and beyond
VO2max declines with age in everyone (see VO2max and ageing). In women, the drop in oestrogen around menopause comes with loss of muscle and bone and a shift towards abdominal fat, which together can speed the decline in relative VO2max. Cardiovascular risk also rises after menopause, which makes fitness even more valuable — low VO2max is a strong predictor of early death (see VO2max and longevity).
The good news is that training works at every age. A meta-analysis by Fitzgerald and colleagues found that women who exercise regularly have a much higher VO2max than sedentary women at every age.
What to prioritise after 45–50:
- One or two hard sessions a week. Intervals are the most efficient stimulus for VO2max; see HIIT vs steady cardio.
- Plenty of easy aerobic work, as in zone 2 training.
- Strength training twice a week to protect muscle and bone; see strength training for runners.
- Sleep and recovery, which hot flushes and night sweats can disrupt.
Estimate your current number with the VO2max calculator, then see your fitness age.
Frequently asked questions
Is my VO2max lower during my period?
On average the change across the cycle is trivial, but some women feel noticeably worse in certain phases, and that is worth respecting on the day.
Can I keep running while pregnant?
Guidelines encourage most women with uncomplicated pregnancies to stay active, with medical clearance and lower intensity as pregnancy progresses.
Does menopause lower VO2max?
VO2max falls with age in both sexes, and the hormonal changes of menopause may add to it, but consistent endurance and interval training slows the decline considerably.
Sources
- McNulty KL, et al. The effects of menstrual cycle phase on exercise performance in eumenorrheic women: a systematic review and meta-analysis. Sports Med, 2020.
- Hunter SK, et al. The biological basis of sex differences in athletic performance: consensus statement for the American College of Sports Medicine. Med Sci Sports Exerc, 2023.
- ACOG Committee Opinion No. 804. Physical activity and exercise during pregnancy and the postpartum period. Obstet Gynecol, 2020.
- Mottola MF, et al. 2019 Canadian guideline for physical activity throughout pregnancy. Br J Sports Med, 2018.
- Fitzgerald MD, et al. Age-related declines in maximal aerobic capacity in regularly exercising vs. sedentary women: a meta-analysis. J Appl Physiol, 1997.
- Mountjoy M, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). Br J Sports Med, 2023.