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HIIT: what the research really shows

Fitness, fat loss and time: what interval training does better, what it doesn’t, and how much you need

Fitness: as good or better, in less time

A meta-analysis of controlled trials found that both interval training and continuous endurance training improved VO2max, the best single measure of aerobic fitness, with intervals improving it slightly more on average 1. In people with heart and metabolic conditions linked to lifestyle, high-intensity intervals improved fitness almost twice as much as moderate continuous exercise 5.

Key study

One minute of hard effort matched 45 minutes of steady cycling

  • Randomized trial
  • 27 inactive men
  • 12 weeks

Three 20-second all-out sprints, in a 10-minute session three times a week, improved fitness, insulin sensitivity and muscle markers as much as 45 minutes of moderate cycling, with a fifth of the exercise time.

Source 2

The time savings show up early, too. Six sessions of 4 to 6 all-out 30-second sprints over two weeks produced muscle and performance changes similar to 90 to 120 minutes of moderate cycling per session, with about 90% less training volume 6.

Fat loss: about the same as steady exercise

In adults with overweight or obesity, interval training and moderate continuous training reduced body fat by similar amounts, but intervals took about 40% less time 3. A larger review found interval training reduced total fat mass a little more than moderate continuous training, mostly with sprint-style intervals, though the difference in kilos was modest 4.

How much do you need?

The World Health Organization recommends 150 to 300 minutes of moderate activity or 75 to 150 minutes of vigorous activity a week, or a mix, plus muscle strengthening on two or more days 7. A few interval sessions a week can cover the vigorous part.

Free toolTry an interval timer nowSet work, rest and rounds in your browser, free.

Sources

  1. Milanović Z, Sporiš G, Weston M. Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials. Sports Med. 2015;45(10):1469-1481. doi.org/10.1007/s40279-015-0365-0
  2. Gillen JB, Martin BJ, MacInnis MJ, et al. Twelve Weeks of Sprint Interval Training Improves Indices of Cardiometabolic Health Similar to Traditional Endurance Training despite a Five-Fold Lower Exercise Volume and Time Commitment. PLoS One. 2016;11(4):e0154075. doi.org/10.1371/journal.pone.0154075
  3. Wewege M, van den Berg R, Ward RE, Keech A. The effects of high-intensity interval training vs. moderate-intensity continuous training on body composition in overweight and obese adults: a systematic review and meta-analysis. Obes Rev. 2017;18(6):635-646. doi.org/10.1111/obr.12532
  4. Viana RB, Naves JPA, Coswig VS, et al. Is interval training the magic bullet for fat loss? A systematic review and meta-analysis comparing moderate-intensity continuous training with high-intensity interval training (HIIT). Br J Sports Med. 2019;53(10):655-664. doi.org/10.1136/bjsports-2018-099928
  5. Weston KS, Wisløff U, Coombes JS. High-intensity interval training in patients with lifestyle-induced cardiometabolic disease: a systematic review and meta-analysis. Br J Sports Med. 2014;48(16):1227-1234. doi.org/10.1136/bjsports-2013-092576
  6. Gibala MJ, Little JP, van Essen M, et al. Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. J Physiol. 2006;575(3):901-911. doi.org/10.1113/jphysiol.2006.112094
  7. Bull FC, Al-Ansari SS, Biddle S, et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med. 2020;54(24):1451-1462. doi.org/10.1136/bjsports-2020-102955
  8. Wisløff U, Støylen A, Loennechen JP, et al. Superior Cardiovascular Effect of Aerobic Interval Training Versus Moderate Continuous Training in Heart Failure Patients. Circulation. 2007;115(24):3086-3094. doi.org/10.1161/CIRCULATIONAHA.106.675041

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Cero’s simple timer on iPhone 18 Pro, with the green wave about half full during a high-intensity interval

Cero is a timer, not a medical device. If you’re new to hard exercise, are pregnant or have a health condition, check with your doctor first, and stop if you feel unwell.