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Cardio

What cardio does to your body

Cardio does far more than burn calories: it changes your heart, blood vessels, brain and metabolism. Here's what the research shows, how much you need, and how to structure it.

§ 01Effects

Six systems it changes

Heart and blood vessels
Regular aerobic training lowers resting blood pressure — by about 3.5/2.5 mmHg on average across trials, and more in people who already have high blood pressure.[2]
Brain and mood
Exercise raises BDNF, a protein that supports brain cells.[3] In adults over 50, it improves thinking skills.[4] It is also an effective treatment for symptoms of depression and anxiety.[5]
Blood sugar
It makes your muscles more sensitive to insulin. In one 12-week trial, three 20-second all-out sprints per session improved insulin sensitivity as much as 50 minutes of steady cycling.[6]
Lifespan
Cardiorespiratory fitness is one of the strongest predictors of how long you'll live.[8] In a study of 122,000 adults, low fitness carried a mortality risk comparable to or greater than smoking or diabetes.[7]
Stamina
Training builds more capillaries and mitochondria in your muscles, so the same effort takes less out of you. That's what "stamina" is.
Sleep
Regular exercise improves sleep quality and helps you fall asleep faster.[9]

§ 02Dose

How much you need

The WHO recommends that adults get 150–300 minutes a week of moderate activity, or75–150 minutes of vigorous activity, or a mix of both, plus muscle-strengthening exercise on two or more days.[1] Any amount is better than none.

Moderate

You can talk in full sentences but couldn't sing. Brisk walking, easy cycling, swimming. Most of your weekly cardio can be this.

Vigorous

You can only say a few words at a time. Running, hill intervals, sprints. One minute of vigorous activity counts as about two minutes of moderate.[1]

§ 03Types

Running, sprints and cycling

  1. 01

    Running

    Builds aerobic fitness efficiently. Beginners can start with run-walk intervals. Increase distance gradually and avoid sudden jumps. In a 5,200-runner study, the clearest injury warning sign was a single run much longer than your longest run in the previous 30 days.[10] The popular "10% per week" rule on its own didn't reduce injuries in a trial.[11] Recreational running is not linked to a higher risk of knee or hip arthritis.[16]

  2. 02

    Sprint intervals

    Very short, all-out efforts give real results in little time. A proven format: warm up, then 3 × 20-second all-out sprints on a bike or a hill, with about 2 minutes of easy movement between each.[6] Build up gradually. If you have heart disease or risk factors for it, check with a doctor first.

  3. 03

    Cycling

    Low-impact and easy on the joints, so it's a good choice if you're heavier or returning from injury. Steady rides build your aerobic base, and hills add intensity.

For men

Stamina and sexual health

Erections depend on healthy blood flow, and aerobic exercise improves the health of the blood vessels involved. That's also why erectile difficulty can be an early warning sign of heart disease. A systematic review found that about 160 minutes a week of moderate-to-vigorous aerobic activity for six monthsimproved erectile function in men with erectile dysfunction caused by physical inactivity, obesity, high blood pressure or heart disease.[12]

If erectile difficulty persists, see a doctor. They can check your blood pressure, blood sugar and cholesterol.

For women

Cardio, bones and hormones

  • Bone density. Walking alone has only a small effect. Impact activities like jogging and jumping, and especially progressive resistance training, protect bone density more effectively. This matters most after menopause.[13]
  • PCOS. Lifestyle programmes that combine exercise and diet improve weight and insulin resistance in women with PCOS.[14]
  • Your cycle. On average, performance changes only slightly across the menstrual cycle, and it varies a lot between women. Train by how you feel rather than a rigid schedule.[17]

§ 04Compare

Outdoors or treadmill?

Both work. The best choice is the one you'll actually stick with.

OutdoorsTreadmill
Energy costSlightly higher, because of air resistanceSet a 1% incline to match outdoor effort[15]
DaylightMorning light helps set your body clock, and sunlight helps your skin make vitamin DNeither
TerrainVaried surfaces and hillsEven surface and precise pacing
PracticalityDepends on weather, air quality and safetyWorks in any weather; useful on high-pollution days

References

  1. 1.World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine, 2020.doi:10.1136/bjsports-2020-102955
  2. 2.Exercise training for blood pressure: a systematic review and meta-analysis. Journal of the American Heart Association, 2013.doi:10.1161/JAHA.112.004473
  3. 3.A meta-analytic review of the effects of exercise on brain-derived neurotrophic factor. Journal of Psychiatric Research, 2015.doi:10.1016/j.jpsychires.2014.10.003
  4. 4.Exercise interventions for cognitive function in adults older than 50: a systematic review with meta-analysis. British Journal of Sports Medicine, 2017.doi:10.1136/bjsports-2016-096587
  5. 5.Effectiveness of physical activity interventions for improving depression, anxiety and distress: an overview of systematic reviews. British Journal of Sports Medicine, 2023.doi:10.1136/bjsports-2022-106195
  6. 6.Twelve weeks of sprint interval training improves indices of cardiometabolic health similar to traditional endurance training. PLOS ONE, 2016.doi:10.1371/journal.pone.0154075
  7. 7.Association of cardiorespiratory fitness with long-term mortality among adults undergoing exercise treadmill testing. JAMA Network Open, 2018.doi:10.1001/jamanetworkopen.2018.3605
  8. 8.Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events: a meta-analysis. JAMA, 2009.doi:10.1001/jama.2009.681
  9. 9.The effects of physical activity on sleep: a meta-analytic review. Journal of Behavioral Medicine, 2015.doi:10.1007/s10865-015-9617-6
  10. 10.How much running is too much? Identifying high-risk running sessions in a 5200-person cohort study. British Journal of Sports Medicine, 2025.doi:10.1136/bjsports-2024-109380
  11. 11.No effect of a graded training program on the number of running-related injuries in novice runners. American Journal of Sports Medicine, 2007.doi:10.1177/0363546507307505
  12. 12.Physical activity to improve erectile function: a systematic review of intervention studies. Sexual Medicine, 2018.doi:10.1016/j.esxm.2018.02.001
  13. 13.Exercise for preventing and treating osteoporosis in postmenopausal women. Cochrane Database of Systematic Reviews, 2011.doi:10.1002/14651858.CD000333.pub2
  14. 14.Lifestyle changes in women with polycystic ovary syndrome. Cochrane Database of Systematic Reviews, 2019.doi:10.1002/14651858.CD007506.pub4
  15. 15.A 1% treadmill grade most accurately reflects the energetic cost of outdoor running. Journal of Sports Sciences, 1996.doi:10.1080/02640419608727717
  16. 16.The association of recreational and competitive running with hip and knee osteoarthritis: a systematic review and meta-analysis. Journal of Orthopaedic & Sports Physical Therapy, 2017.doi:10.2519/jospt.2017.7137
  17. 17.The effects of menstrual cycle phase on exercise performance in eumenorrheic women: a systematic review and meta-analysis. Sports Medicine, 2020.doi:10.1007/s40279-020-01319-3

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