The Science of High Intensity Interval Training (HIIT) Tabata and Wingate

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	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	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	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	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	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	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	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	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	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 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.

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 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.

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, 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. 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.

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. This is backed up by studies of some of the great endurance athletes, where higher training mileage produced worse rather than better performance. 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". Of course this is not universally true, and Mike Morton, set the US record holder for 24 hour while training 140-150 miles/week. 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
• 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. 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 T_lim , where T_lim is the time to exhaustion at 100% V̇O₂max.
• 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). The HIIT training consisted of 2 sessions per week of 6 intervals at 100% V̇O₂max with time varying between 60-75% T_lim, plus one weekly run of 30 min at 60% vV̇O₂max. For these runners, T_lim 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% T_lim (133 sec) or 5x 70% (154 sec) T_lim, resting for twice the interval time. Their 3K time improved by 17.6 sec (60% T_lim) or 6.3 sec (70% T_lim), but there was no change in their 5K time.
• 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. Note that groups 1 and 2 vary only in their rest time, which is based on Heart Rate dropping to 65% of HR_max 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.

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.