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To run HIIT intervals requires a longer stride length, so other modes, such as a stationary bike may be more appropriate.

This page looks at the scientific evidence on High Intensity Interval Training (HIIT), divided into three sections. Studies that compare HIIT with other modes of training are the most interesting, though they often don't cover highly trained athletes. I've included a few other studies that are not comparative because they have some particularly dramatic results. The third section looks at the studies that have looked at HIIT for highly trained athletes. For an introduction to HIIT, see High Intensity Interval Training.

1 Components of HIIT

There are three main variable that shape a HIIT workout.

  • Intensity. I'd argue that to be considered "high intensity" the workout should be higher than Lactate Threshold, and really, I'd consider it to be at least 100% of the effort at VO2max. The classic Tabata workout used 1.7x the work at VO2max, though many implementations of this workout simply use "all out."
  • Duration. Given intensities at or above VO2max, the duration needs to be quite short, and it's often 30 seconds or less.
  • Recovery. The recovery period can be extremely short, which tends to mimic some of the characteristics of a lower intensity, longer duration interval. At the other extreme, the recovery can be long enough to ensure nearly complete recovery, typically taking several minutes. The recovery intensity can be active, but the effort is nearly always fairly low.

2 HIIT Comparisons on Untrained or Moderately Active Subjects

The table below looks at studies that have compared HIIT with other types of training, often Continuous Moderate Exercise (CME). These studies on untrained or moderately trained subjects generally show a greater improvement in fitness measure compared with other forms of training, or similar improvements for far less training time.

Study Subjects Study length Protocol Outcome Best Result Notes

Tabata-1996[1]

14 varsity level collage athletes (V̇O2max ~50)

5 days/week 6 weeks

HIIT (HIIT-SIx170)

4 days/week 7-8x (20 seconds at 170% V̇O2max + 10 seconds rest) 1 day/week 30 min at 70% V̇O2max + 4x (30 seconds at 170% V̇O2max + 10 seconds rest)

Raised V̇O2max by 14.5%

Increased anaerobic capacity by 28%

HIIT

HIIT produced a greater improvement in V̇O2max for far less time commitment

Continuous Moderate Exercise

60 minutes at 70% V̇O2max

Raised V̇O2max by 9.5%

No change in anaerobic capacity

Helgerud-2007[2]

Moderately trained (V̇O2max 51-55)

3 days/week 8 weeks

Short HIIT (HIIT-SIx90)

47x 15 seconds at 90-95% HRmax + 15 seconds at 70% HRmax

Raised V̇O2max 5.5%

Short and Long HIIT (no statistical difference)

All groups improved economy, with no differences, and Lactate Threshold unchanged as a percentage of V̇O2max

Long HIIT (HIIT-LCx90)

4x 4 min, 90-95% HRmax + 3 min at 70%max

Raised V̇O2max 7.2%
Lactate Threshold run

24 min at 85% HRmax

V̇O2max unchanged
Long Slow Distance

45 minutes at 70% HRmax

V̇O2max unchanged

TjonnaLee-2008[3]

Untrained, metabolic syndrome patients

3 days/week 16 weeks

HIIT (HIIT-LCx90)

4x 4 min at 90% HRmax + 3 min 70% HRmax total 40 min,

Raised V̇O2max 36%

HIIT

Same calories burned in each group Both groups had an equal reduction in body weight and blood pressure

Continuous Moderate Exercise

47 min at 70% HRmax

Raised V̇O2max 16%

Gibala-2006[4]

Recreationally active

2 weeks

HIIT (HIIT-SCx260)

4-6x 30 seconds 'all out' + 4 min recovery (260%) Totals for two weeks, 135 minutes and 950 Kj

Same improvement in laboratory time trials

HIIT

Same improvement, but only 22% of the time commitment

Continuous Moderate Exercise

90-120 min at 65% V̇O2peak Totals for two weeks, 630 minutes and 6500 Kj

Gorostiaga-1991[5]

Sedentary

3 days/week 8 weeks

HIIT (HIIT-SIx100)

30x 30 sec @ 100% V̇O2max + 30 sec rest

Raised V̇O2max 9-16%

HIIT

Same average work in each group

Continuous Moderate Exercise

30 minutes at 50% V̇O2max

Raised V̇O2max 5-7%

Franch-1998[6]

36 recreational runners

3 days/week at high intensity Plus 3 runs/week <= 65% HRmax 6 weeks

Short HIIT (HIIT-SIx90)

30-40x 15 sec run, 15 sec rest Avg ~3.0 Km/workout 92% HRmax

Time to exhaustion increased 65%

Running Economy improved 0.9%

Continuous High Intensity

Better improvements from continuous training than HIIT, but the continuous training is at an unusually high intensity that is probably close to a 10K race, three times a week.

Long HIIT (HIIT-LCx90)

4-6x 4 min run, 2 min rest Avg ~5.6 Km/workout 94% HRmax

Time to exhaustion increased 67%

Running Economy improved 3.0%

Continuous High Intensity

20-30 minutes Avg ~6.4 Km/workout 93% HRmax

Time to exhaustion increased 94%

Running Economy improved 3.1%

BurgomasterHowarth-2007[7]

20 Untrained

HIIT 3x week Continuous 5x week 6 weeks

HIIT (HIIT-SCxAO)

4-6x 30 seconds 'all out', 4.5 min rest 1.5 hours/week ~225 Kj/week

Both increased V̇O2peak by ~5%

HIIT

Similar changes in HIIT for 10% of the workload and 30% of the time of continuous training.

Continuous Moderate Exercise

40-60 min at 65% V̇O2peak 4.5 hours/week 2250 Kj/week

Trapp-2008[8]

34 sedentary women

45 workouts over 15 weeks

HIIT (HIIT-SIxAO)

60x 8 seconds 'all out', 12 seconds rest (5 min Warmup, 20 min conditioning, 5 min Cooldown)

Increased V̇O2peak 24%

5 pound/2.5 Kg reduction in body fat Significant 31% reduction in fasting insulin Significant reduction in Leptin

HIIT

HIIT produced similar improvements in fitness for a lower time commitment, as well as a reduction in body fat that was not seen with continuous exercise.

Continuous Moderate Exercise

40 minutes at 60% V̇O2peak

Increased V̇O2peak 19%

1 pound/0.5 Kg gain in body fat Non-significant 9% reduction in fasting insulin No change in Leptin

EarnestTjønna-2013[9]

26 healthy overweight men (BMI 25-30)

3 days/week 10 weeks

4x HIIT (HIIT-LCx90)

10 min Warmup 4x 4 min at 90% HRmax + 3 min 70% HRmax 5 min Cooldown total 40 min

Raised V̇O2max by 13%

Work economy improved by 13% Systolic blood pressure decreased 3.2 mmHg Diastolic blood pressure decreased 6.3 mmHg

Similar results with both protocols

This study showed remarkable results using a single high intensity bout of exercise.

1x HIIT (HIIT-LCx90)

10 min Warmup 4 min at 90% HRmax 5 min Cooldown total 19 min

Raised V̇O2max by 10%

Work economy improved by 14% Systolic blood pressure decreased 6.2 mmHg Diastolic blood pressure decreased 7.7 mmHg

2.1 Aerobic High-Intensity Intervals Improve VO2Max More Than Moderate Training

This study[2] was on 40 male university students, all physically active and with VO2max of 55-60, which is translates to marathon times of 2:55 to 2:43, so they're pretty fit. The four running based training interventions were designed to have the same amount of total work, which makes this study a little unusual as often HIIT requires far less work than other approaches. Each program included 3 workouts per week and lasted for 8 weeks. The training is described in the table above, and all performed on a treadmill at 5.3% incline. I noticed that the LSD is somewhat higher intensity 70% Maximum Heart Rate, and shorter 45 min than I'd expect for typical LSD training. The Lactate Threshold was defined as 1.5 mmol/l above resting, which is slightly odd, but no worse than most protocols that don't use the gold standard of Maximum Lactate Steady State. The LSD and LT runs decreased the speed of the treadmill as the heart rate rose due to drift. The short interval protocol was based around 15 seconds at 90-95% Maximum Heart Rate with 15 seconds recovery, which seems to translate to a fairly steady state heart rate. They did 47 repetitions, which is quite a stunning number, and far more than I'd have expected to be doable. By comparison, the four repeats of 4 minutes with 3-minute recoveries is rather more mainstream. All four protocols burned similar levels of oxygen.

Heart rate for the four interventions, top left to bottom right: LSD, Lactate Threshold, 47x15+15, 4x4+3.

The results were that VO2max went down fractionally for LSD and up fractionally for Lactate Threshold, though neither was a significant change from baseline. The two interval training approaches raised VO2max with no significant difference, though the 4x4 was slightly better than the 47x15. Running Economy and Lactate Threshold were unchanged for all groups.

Helgerud-2007-Vo2max.jpg

Conclusion: this study suggests that high intensity training can improve the aerobic capacity of relatively fit subjects, while LSD and lactate threshold training is ineffective. However, the structure of the short intervals is rather unusual, and atypical, and I'm not sure I would consider either protocol truly "HIIT".

2.2 Aerobic Interval Training Versus Continuous Moderate Exercise as a Treatment for the Metabolic Syndrome

This is a similar study[3] to the one above, both from "Norwegian University of Science and Technology", though the researchers appear different. The subjects are certainly different, as they are 32 patients with metabolic syndrome, average VO2max is 34, which translates to about a 4:20 marathon. This study used just two training programs; 47 minutes at 70% of Maximum Heart Rate or four intervals of 4 minutes at 70% of Maximum Heart Rate with 3-minute recoveries. Each program included 3 workouts per week and lasted for 16 weeks, consisting of walking/running on an incline treadmill. The intervals resulted in a greater improvement in VO2max, and better mitigation of the risk factors associated with metabolic syndrome.
Conclusion: this extends the previous study's finding to less fit subjects who have medical issues.

2.3 Short-term sprint interval versus traditional endurance training

3 HIIT Studies on Untrained or Moderately Active Subjects without Controls

While studies that compare HIIT with other forms of training are the most useful, there are a few other studies on untrained or moderately active people that are noteworthy. For instance, six sessions of HIIT over two weeks doubled the endurance of untrained subjects at 80% V̇O2max from 25 to 51 minutes, despite no change in V̇O2max[10], a remarkable improvement. In another study, the combination of Continuous Moderate Exercise and moderate intensity intervals (60-70% V̇O2max) reduced body fat by 15%, which was nine times more than Continuous Moderate Exercise alone, even though the Continuous Moderate Exercise burned over twice the calories[11]. Another study also used a combination of HIIT on 3 day/week plus running as far as possible in 40 min on another 3 days/week , resulting in an increase in V̇O2max by 44%, as well as improved running endurance, with some subjects ending up with a V̇O2max exceeding 60 ml/kg per min, which is remarkably high for 10 weeks of training[12].

4 HIIT and Highly Trained Athletes

It has been suggested that elite athletes do not benefit from further increases in volume, and should instead look to HIIT for performance improvements[13]. This is backed up by studies of some of the great endurance athletes, where higher training mileage produced worse rather than better performance[14]. In the Lore of Running, Tim Noakes said that elite runners perform best "when they train between 75-125 miles (120-200 km) per week, with an increasing likelihood that they will perform indifferently when they train more than 125 miles (200 km) per week"[15]. Of course this is not universally true, and Mike Morton, set the US record holder for 24 hour while training 140-150 miles/week[16]. However, the evaluation of HIIT on elite athletes is not as easy as lessor folk. It's not practical to compare the effect of HIIT with other forms of exercise in highly trained athletes as they are typically already performing large volumes of Continuous Moderate Exercise. Instead, studies of highly trained athletes look at how HIIT impacts their fitness compared with a baseline taken beforehand.

  • HIIT improved peak power output and 40 Km time trial in elite cyclists[17][18]
  • A study of elite cyclists used various HIIT workouts as shown in the table below, with the best results seen group 4 or group 1[19]. Group 4 trained at 85% peak power, which corresponds to the intensity normally seen in the 40K time trial, which takes ~60 minutes for an elite cyclist. Not surprisingly, this intensity is commonly used for cyclists training for 40K time trials. However, the higher intensity of group 1 is more intriguing; the time trial performance improved without an improvement in peak power, suggesting that a different mechanism may be responsible. This raises the possibility that the benefits of the different intensities might be combined. Note that there were only four athletes in each group, and responses tended to vary, so caution should be used in interpreting the results.
Group Number of intervals Interval duration (min) Total work time (min) Intensity (% peak power) Rest (min) Total Time Improvement in 40K Time Trial Speed Improvement in Peak Power
1 12 0.5 6 175% 4.5 60 min 2.0% 0.5%
2 12 1 12 100% 4.0 60 min 0.0% 0.5%
3 12 2 24 90% 3.0 60 min 1.5% 1.5%
4 8 4 32 85% 1.5 44 min 2.5% 2.0%
5 4 8 32 80% 1.0 36 min 0.0% 1.0%
  • One approach to optimizing the length of the intervals in highly trained athletes is to use a percentage of Tlim , where Tlim is the time to exhaustion at 100% V̇O2max[13].
  • 5 state level middle distance runners that underwent 4 weeks of HIIT training reduced their 3K time by 2.8% (10:16 to 9:59) and V̇O2max by 4.9% (61 to 64)[20]. The HIIT training consisted of 2 sessions per week of 6 intervals at 100% V̇O2max with time varying between 60-75% Tlim, plus one weekly run of 30 min at 60% vV̇O2max. For these runners, Tlim averaged 225 seconds, so the intervals were between 135 and 170 seconds.
  • Well trained, competitive runners trained twice a week for four weeks with intervals at 100% V̇O2max for either 6x 60% Tlim (133 sec) or 5x 70% (154 sec) Tlim, resting for twice the interval time. Their 3K time improved by 17.6 sec (60% Tlim) or 6.3 sec (70% Tlim), but there was no change in their 5K time[21].
  • 41 elite (V̇O2peak ~65) cyclists and triathletes were split into four groups, with three groups using the HIIT described below and the fourth acting as a control that followed only low to moderate intensity training[22]. Note that groups 1 and 2 vary only in their rest time, which is based on Heart Rate dropping to 65% of HRmax in group 2 (averaging around 180 seconds). This was a demanding regime, as the subjects reached exhaustion on nearly every HIIT training session, with only 64% of the dictated intervals actually completed. Note that like comparison of different workouts above, the shorter HIIT produced a similar improvement in 40K performance without the accompanying rise in V̇O2max which was not statistically different between group 3 and the controls.
Group Intended number of intervals Interval Duration Total work time (min) Intensity (% V̇O2max) Rest Total time V̇O2max change 40K Time Trial Speed improvement
1 8 60% Tlim(~150 sec) 20 100% 120% Tlim (~290 sec) 58 min 5.2% 5.2%
2 8 60% Tlim(~150 sec) 20 100% 65% HRmax (~180 sec) Varies 8.0% 5.6%
3 12 30 seconds 6 175% 4.5 min 60 min 3.1% 4.3%
Control N/A N/A N/A N/A N/A N/A 0.8% -1%
  • Elite cyclists performed 4 sessions of HIIT (20x 60 sec at V̇O2max + 120 sec recovery) that improved peak power by 4% but had no change in V̇O2max[23].

5 Limitations of the HIIT science

There are some important limitations of the HIIT science.

  • The majority of studies are on sedentary or recreationally active people, not trained runners.
  • Few studies use real world measures of improvement, relying instead on indirect metrics such as V̇O2max. While V̇O2max is linked to improved performance, there are other important factors involved.
  • Studies that do look at the effect of HIIT on real world performance tend to focus on shorter events, such as 3K or 5K running, or 40K cycling.
  • Most studies are short duration, looking at the effects of HIIT over just a few weeks.

6 References

  1. ↑ I. Tabata, K. Nishimura, M. Kouzaki, Y. Hirai, F. Ogita, M. Miyachi, K. Yamamoto, Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max., Med Sci Sports Exerc, volume 28, issue 10, pages 1327-30, Oct 1996, PMID 8897392
  2. ↑ 2.0 2.1 J. Helgerud, K. Høydal, E. Wang, T. Karlsen, P. Berg, M. Bjerkaas, T. Simonsen, C. Helgesen, N. Hjorth, Aerobic high-intensity intervals improve VO2max more than moderate training., Med Sci Sports Exerc, volume 39, issue 4, pages 665-71, Apr 2007, doi 10.1249/mss.0b013e3180304570, PMID 17414804
  3. ↑ 3.0 3.1 A. E. Tjonna, S. J. Lee, O. Rognmo, T. O. Stolen, A. Bye, P. M. Haram, J. P. Loennechen, Q. Y. Al-Share, E. Skogvoll, S. A. Slordahl, O. J. Kemi, S. M. Najjar, U. Wisloff, Aerobic Interval Training Versus Continuous Moderate Exercise as a Treatment for the Metabolic Syndrome: A Pilot Study, Circulation, volume 118, issue 4, 2008, pages 346–354, ISSN 0009-7322, doi 10.1161/CIRCULATIONAHA.108.772822
  4. ↑ MJ. Gibala, JP. Little, M. van Essen, GP. Wilkin, KA. Burgomaster, A. Safdar, S. Raha, MA. Tarnopolsky, Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance., J Physiol, volume 575, issue Pt 3, pages 901-11, Sep 2006, doi 10.1113/jphysiol.2006.112094, PMID 16825308
  5. ↑ EM. Gorostiaga, CB. Walter, C. Foster, RC. Hickson, Uniqueness of interval and continuous training at the same maintained exercise intensity., Eur J Appl Physiol Occup Physiol, volume 63, issue 2, pages 101-7, 1991, PMID 1748098
  6. ↑ J. Franch, K. Madsen, MS. Djurhuus, PK. Pedersen, Improved running economy following intensified training correlates with reduced ventilatory demands., Med Sci Sports Exerc, volume 30, issue 8, pages 1250-6, Aug 1998, PMID 9710865
  7. ↑ K. A. Burgomaster, K. R. Howarth, S. M. Phillips, M. Rakobowchuk, M. J. MacDonald, S. L. McGee, M. J. Gibala, Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans, The Journal of Physiology, volume 586, issue 1, 2007, pages 151–160, ISSN 0022-3751, doi 10.1113/jphysiol.2007.142109
  8. ↑ EG. Trapp, DJ. Chisholm, J. Freund, SH. Boutcher, The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women., Int J Obes (Lond), volume 32, issue 4, pages 684-91, Apr 2008, doi 10.1038/sj.ijo.0803781, PMID 18197184
  9. ↑ Conrad P. Earnest, Arnt Erik Tjønna, Ingeborg Megaard Leinan, Anette Thoresen Bartnes, Bjørn M. Jenssen, Martin J. Gibala, Richard A. Winett, Ulrik Wisløff, Low- and High-Volume of Intensive Endurance Training Significantly Improves Maximal Oxygen Uptake after 10-Weeks of Training in Healthy Men, PLoS ONE, volume 8, issue 5, 2013, pages e65382, ISSN 1932-6203, doi 10.1371/journal.pone.0065382
  10. ↑ KA. Burgomaster, SC. Hughes, GJ. Heigenhauser, SN. Bradwell, MJ. Gibala, Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans., J Appl Physiol, volume 98, issue 6, pages 1985-90, Jun 2005, doi 10.1152/japplphysiol.01095.2004, PMID 15705728
  11. ↑ A. Tremblay, JA. Simoneau, C. Bouchard, Impact of exercise intensity on body fatness and skeletal muscle metabolism., Metabolism, volume 43, issue 7, pages 814-8, Jul 1994, PMID 8028502
  12. ↑ RC. Hickson, HA. Bomze, JO. Holloszy, Linear increase in aerobic power induced by a strenuous program of endurance exercise., J Appl Physiol, volume 42, issue 3, pages 372-6, Mar 1977, PMID 838658
  13. ↑ 13.0 13.1 PB. Laursen, DG. Jenkins, The scientific basis for high-intensity interval training: optimising training programmes and maximising performance in highly trained endurance athletes., Sports Med, volume 32, issue 1, pages 53-73, 2002, PMID 11772161
  14. ↑ An Interesting Analysis of Some Elites’ Training History, Accessed on 26 February 2013
  15. ↑ Timothy Noakes, Lore of runnin, date 2003, publisher Human Kinetics, location Champaign, IL, isbn 0-87322-959-2, pages 447*448
  16. ↑ http://militarytimes.com/blogs/pt365/2012/05/07/army-master-sgt-mike-morton-and-his-14-year-journey-to-the-badwater-135-ultramarathon/, http://militarytimes.com/blogs/pt365/2012/05/07/army-master-sgt-mike-morton-and-his-14-year-journey-to-the-badwater-135-ultramarathon/, Accessed on 26 February 2013
  17. ↑ FH. Lindsay, JA. Hawley, KH. Myburgh, HH. Schomer, TD. Noakes, SC. Dennis, Improved athletic performance in highly trained cyclists after interval training., Med Sci Sports Exerc, volume 28, issue 11, pages 1427-34, Nov 1996, PMID 8933495
  18. ↑ C. Westgarth-Taylor, JA. Hawley, S. Rickard, KH. Myburgh, TD. Noakes, SC. Dennis, Metabolic and performance adaptations to interval training in endurance-trained cyclists., Eur J Appl Physiol Occup Physiol, volume 75, issue 4, pages 298-304, 1997, PMID 9134360
  19. ↑ NK. Stepto, JA. Hawley, SC. Dennis, WG. Hopkins, Effects of different interval-training programs on cycling time-trial performance., Med Sci Sports Exerc, volume 31, issue 5, pages 736-41, May 1999, PMID 10331896
  20. ↑ TP. Smith, LR. McNaughton, KJ. Marshall, Effects of 4-wk training using Vmax/Tlim on VO2max and performance in athletes., Med Sci Sports Exerc, volume 31, issue 6, pages 892-6, Jun 1999, PMID 10378918
  21. ↑ TP. Smith, JS. Coombes, DP. Geraghty, Optimising high-intensity treadmill training using the running speed at maximal O(2) uptake and the time for which this can be maintained., Eur J Appl Physiol, volume 89, issue 3-4, pages 337-43, May 2003, doi 10.1007/s00421-003-0806-6, PMID 12736843
  22. ↑ PB. Laursen, CM. Shing, JM. Peake, JS. Coombes, DG. Jenkins, Interval training program optimization in highly trained endurance cyclists., Med Sci Sports Exerc, volume 34, issue 11, pages 1801-7, Nov 2002, doi 10.1249/01.MSS.0000036691.95035.7D, PMID 12439086
  23. ↑ PB. Laursen, MA. Blanchard, DG. Jenkins, Acute high-intensity interval training improves Tvent and peak power output in highly trained males., Can J Appl Physiol, volume 27, issue 4, pages 336-48, Aug 2002, PMID 12442351
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