High Intensity Interval Training

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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.

High Intensity Interval Training (HIIT) uses repeated short periods of very intense cardiovascular exercise separated by lower intensity recoveries. HIIT has been shown to improve aerobic capacity in untrained and moderately active individuals more quickly than Continuous Moderate Exercise, as well as having potential benefits for highly trained athletes. HIIT has also been shown to reduce body fat in untrained people more effectively than Continuous Moderate Exercise. However, there is no evidence to suggest that HIIT can replace other forms of training for endurance races.

1 What is HIIT?

High Intensity Interval Training is a form of Interval Training using short intervals of 10 seconds to 5 minutes at an intensity at or above 90% V̇O2max[1]. High Intensity Interval Training, abbreviated to HIIT or HIT, is sometimes called High-Intensity Intermittent Exercise[2] or Sprint Training[3].

2 HIIT Recommendations

Below are my recommendations based on my interpretation of the available evidence. These recommendations for incorporating HIIT in your training depend on your current fitness goals.

  • For sedentary people, HIIT is probably more effective in building initial fitness than Continuous Moderate Exercise. Three sessions per week of Wingate HIIT on a stationary bike should provide an improvement in fitness for a modest time commitment. Using WinTab style HIIT may produce similar benefits for a lower time commitment.
  • For people looking to lose weight, HIIT will probably produce a greater reduction in body fat than Continuous Moderate Exercise. Three sessions per week of Wingate HIIT on a stationary bike should help with weight loss and appetite control. The HIIT could be combined with other forms of exercise on the other days, which may further improve weight loss. (HIIT probably more effective than Continuous Moderate Exercise at improving insulin sensitivity.)
  • Recreationally active people looking for rounded fitness may benefit from including HIIT in their overall training program. Adding 1-3 sessions per week of Wingate or WinTab HIIT on a stationary bike should provide an improvement in fitness.
  • Athletes focused on improving their performance in endurance races lasting less than an hour will probably benefit from replacing some of their training load with a combination of both traditional HIIT and shorter Wingate or WinTab style HIIT. Up to one traditional HIIT or 1-3 shorter HIIT sessions could be included in a weekly training routine. Care should be taken to increase Training Load slowly with the additional HIIT and try to avoid increasing Training Monotony. The traditional HIIT should be performed by running on a track or other outdoor location. For the shorter HIIT, a stationary bike probably has a lower injury risk, but the additional benefits of outdoor running may outweigh the additional injury risk. However, the fast paces of the shorter HIIT should be introduced gradually, building up the pace over a number of workouts.
  • There is no direct evidence to indicate if HIIT will help athletes focused on improving their performance in events lasting longer than an hour. However, it seems reasonable that HIIT would provide some benefits. Including 1 or 2 Wingate or WinTab HIIT sessions per week may be appropriate. As noted in the prior bullet point for shorter duration athletes, care should be taken to monitor Training Load and Training Monotony. As with athletes focusing on events lasting less than an hour, the stationary bike has the lowest injury risk, but there may be benefits to other training modes. However, athletes competing in longer duration events typically don't have the same need for the very high paces that are sometimes seen at the end of shorter events.
  • There is no evidence to suggest that HIIT can be used to replace Continuous Moderate Exercise such as the Long Run that is a core part of endurance training.

3 Types of HIIT

There are various different protocols for performing HIIT. While the Tabata is probably the most widely recognized name in HIIT, it is one of the least studied and the least used.

3.1 Tabata

Main article: Tabata The Tabata workout is one of the best known protocols for HIIT and consists of 7-8 repeats of 20 seconds at 170% of V̇O2max with 10 seconds rest. The number of repetitions is defined by how long the required intensity can be maintained. An athlete should be able to complete 7-8 intervals; if 9 can be performed, the intensity is increased. However, few people actually follow the Tabata protocol because it requires specialist equipment to measure V̇O2max, then calculate 1.7x the V̇O2max workload that should be used. In practice, most people do what I call the WinTab workout (see below).

3.2 Wingate

This style of HIIT is based around the Wingate test, which is used to measure peak anaerobic power and anaerobic capacity[4]. The Wingate HIIT uses 30 seconds of 'all out' intensity, followed by ~4 minutes of recovery, repeated 4-6 times.

3.3 WinTab (Tabata style Wingate)

Most athletes that use the Tabata workout do not use the 170% V̇O2max intensity, but rather the Wingate style 'all out' intensity. Because the intensity is not fixed, the WinTab normally has 8 repetitions of 20 seconds all out plus 10 seconds rest, taking 5 minutes (plus Warmup), rather than the variable number of repetitions of the original Tabata protocol.

3.4 Traditional Anaerobic Intervals

High intensity Interval Training has been in use since before the Tabata study made the term popular. The Jack Daniel's 'R' paced workouts are a classic example of this tradition of anaerobic interval training. The Jack Daniel's 'R' intervals are performed at around mile/1500m pace[5], which is generally close to 100% V̇O2max. The 'R' workouts are 12-40 repeats of 30-60 seconds with 1-4 min rests[6]. Jack Daniels mentions once having his athletes perform over 1,000 repetitions of one minute HIIT (4 minute rest) in a 14 day period, with two male athletes averaging 5:00 min/mile pace and therefore covering 250 miles[6].

4 HIIT Training Mode

There are various ways that HIIT could be performed, each with their own pros and cons.

Mode Pros Cons
Stationary Bike
  • The vast majority of studies have used a stationary bike to perform HIIT.
  • A direct measure of intensity through power is often possible.
  • Lowest risk of injury.
  • The bike does use the same muscles as running.
Bike
  • Should be similar to the stationary bike, but at a lower cost.
  • It's easier to ride a bike out of the saddle than a stationary bike, which uses more muscles and is closer to the action of running.
  • Riding a bike at high intensity adds risk due to impaired mental functioning and coordination.
  • While it's possible to directly measure power output on a bike, it's expensive.
Running
  • For runners, the right muscle groups are trained.
  • At high Intensity, the movements involved in running become dramatically different, requiring a greater range of motion. This difference creates a significant risk of injury. Running uphill reduces some of this stress (hill based HIIT is not uncommon[7]).
  • The rapid acceleration and deceleration of HIIT creates stress that runners are not typically exposed to, again creating a risk of injury. (I suspect the risk of injury during the deceleration is often underestimated, as this is when where a runner's form often deteriorates.)
  • Even with a Footpod and a good running watch it's hard to measure pace accurately, and GPS is useless for the short intervals often used in HIIT. Running on a track or other known distance may be slightly easier, but it's still not trivial. (This is not a problem for 'all out' style of HIIT.)
Treadmill
  • It's possible to run in weather that is too hostile for outside activities.
  • Most treadmills will not change pace fast enough for the dramatic changes in pace between interval and recovery used in HIIT.
  • Matching acceleration and deceleration with the treadmill is not easy, especially when mental functioning is impaired, as it so often is at high intensity
  • If you cannot maintain the programmed pace, you could be injured by falling off the back of a treadmill.
  • A treadmill may not be able to go fast enough for HIIT.

5 HIIT Running Paces

I don't generally recommend running HIIT workouts because of the high speeds required. Below is a sampling of the HIIT paces for different fitness levels (V̇O2max). For each level, the 5K and marathon times are given, along with the pace that corresponds to 90%, 100% and 170% of V̇O2max.

V̇O2max 35 40 45 50 55 60 65 70 75 80 85
5K 26:57 24:05 21:50 20:00 18:28 17:10 16:03 15:05 14:15 13:32 12:51
Marathon 4:15:51 3:49:27 3:28:10 3:10:33 2:55:49 2:43:08 2:32:29 2:23:04 2:14:53 2:07:31 2:00:58
90% V̇O2max 9:09/Mile 8:13/Mile 7:28/Mile 6:52/Mile 6:21/Mile 5:55/Mile 5:33/Mile 5:13/Mile 4:56/Mile 4:41/Mile 4:27/Mile
100% V̇O2max 8:24/Mile 7:33/Mile 6:52/Mile 6:18/Mile 5:50/Mile 5:26/Mile 5:05/Mile 4:47/Mile 4:32/Mile 4:18/Mile 4:06/Mile
170% V̇O2max 5:28/Mile 4:54/Mile 4:27/Mile 4:06/Mile 3:48/Mile 3:33/Mile 3:19/Mile 3:08/Mile 2:58/Mile 2:49/Mile 2:41/Mile

6 The HIIT Science

This section looks at the scientific evidence, divided into three sections. Studies that compare HIIT with other modes of training are the most interesting, though they 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.

6.1 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

Helgerud-2007[8]

Moderately trained (V̇O2max 51-55)

3 days/week 8 weeks

Short HIIT

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

Raised V̇O2max 7.2%

Short HIIT

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

Long HIIT

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

Raised V̇O2max 5.5%
Lactate threshold run

24 min at 85% HRmax

V̇O2max unchanged
Long Slow Distance

45 minutes at 70% HRmax

V̇O2max unchanged

TjonnaLee-2008[9]

Untrained, metabolic syndrome patients

3 days/week 16 weeks

HIIT

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[3]

Recreationally active

2 weeks

HIIT

4-6x 30 seconds 'all out' + 4 min recovery 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[10]

Sedentary

3 days/week 8 weeks

HIIT

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

Raised V̇O2max 9-16%

No change in blood lactate during continuous exercise

HIIT

Same average work in each group

Continuous Moderate Exercise

30 minutes at 50% V̇O2max

Raised V̇O2max 5-7%

Reduced blood lactate during continuous exercise by nearly 50%

Franch-1998[11]

36 recreational runners

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

Short HIIT

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

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[12]

20 Untrained

HIIT 3x week Continuous 5x week 6 weeks

HIIT

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[2]

34 sedentary women

45 workouts over 15 weeks

HIIT

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

Tabata-1996[13]

14 varsity level collage athletes (V̇O2max ~50)

5 days/week 6 weeks

HIIT

4 days/week 7-8x (30 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

6.2 HIIT Studies on Untrained or Moderately Active Subjects

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[14], 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[15]. 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[16].

6.3 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[17]. This is backed up by studies of some of the great endurance athletes, where higher training mileage produced worse rather than better performance[18]. 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"[19]. Of course this is not universally true, and Mike Morton, set the US record holder for 24 hour while training 140-150 miles/week[20]. 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[21][22]
  • 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[23]. 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[17].
  • 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)[24]. 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[25].
  • 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[26]. 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[27].

6.4 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.

7 Crossfit Endurance

Crossfit Endurance is a training approach that reduces the normal endurance training volumes while increasing the training intensity[28]. The reduction in volume is quite dramatic compared with other training plans; for instance, the Crossfit Endurance marathon training plan has a 10 mile time trial as its longest run, which is combined with weight training and interval training[29]. While there are some testimonials to the Crossfit Endurance methodology[30], their approach is controversial[31]. The science that is used to support Crossfit Endurance does not support replacing traditional Continuous Moderate Exercise with HIIT for endurance events, only using HIIT as a supplementary form of training[32]. Most of the anecdotal reports suggest that people have set personal records at 5K and 10K distances and completed half marathons using the Crossfit Endurance approach, but there are few reports of longer races. The anecdotal reports are hard to interpret objectively without knowing the individuals prior training methodology.

8 References

  1. ↑ Stephen H. Boutcher, High-Intensity Intermittent Exercise and Fat Loss, Journal of Obesity, volume 2011, 2011, pages 1–10, ISSN 2090-0708, doi 10.1155/2011/868305
  2. ↑ 2.0 2.1 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
  3. ↑ 3.0 3.1 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
  4. ↑ H. Vandewalle, G. Pérès, H. Monod, Standard anaerobic exercise tests., Sports Med, volume 4, issue 4, pages 268-89, PMID 3306867
  5. ↑ Jack Daniels, Daniels' running formula, date 2005, publisher Human Kinetics, location Champaign, IL, isbn 0-7360-5492-8
  6. ↑ 6.0 6.1 Jack Daniels, Daniels' running formula, date 2005, publisher Human Kinetics, location Champaign, IL, isbn 0-7360-5492-8, pages 132
  7. ↑ How to Complete High-Intensity Interval Hill Workouts, http://www.active.com/running/Articles/How-to-Complete-High-Intensity-Interval-Hill-Workouts, Accessed on 24 February 2013
  8. ↑ 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
  9. ↑ 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
  10. ↑ 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
  11. ↑ 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
  12. ↑ 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
  13. ↑ 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
  14. ↑ 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
  15. ↑ 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
  16. ↑ 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
  17. ↑ 17.0 17.1 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
  18. ↑ An Interesting Analysis of Some Elites’ Training History, Accessed on 26 February 2013
  19. ↑ Timothy Noakes, Lore of runnin, date 2003, publisher Human Kinetics, location Champaign, IL, isbn 0-87322-959-2, pages 447*448
  20. ↑ 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
  21. ↑ 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
  22. ↑ 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
  23. ↑ 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
  24. ↑ 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
  25. ↑ 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
  26. ↑ 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
  27. ↑ 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
  28. ↑ About Crossfit Endurance, http://www.crossfitendurance.com/whatiscfe, Accessed on 26 February 2013
  29. ↑ http://www.outsideonline.com/fitness/endurance-training/CrossFit-Endurances-Unconventional-12-Week-Marathon-Training-Plan.html, http://www.outsideonline.com/fitness/endurance-training/CrossFit-Endurances-Unconventional-12-Week-Marathon-Training-Plan.html, Accessed on 26 February 2013
  30. ↑ Testimonials, http://www.crossfitendurance.com/testimonials, Accessed on 26 February 2013
  31. ↑ Science of Running: Crossfit endurance, Tabata sprints, and why people just don’t get it, http://www.scienceofrunning.com/2012/01/crossfit-endurance-tabata-sprints-and.html, Accessed on 26 February 2013
  32. ↑ CrossFit MPH - Washington, DC, http://metamorphitness.wordpress.com/nutrition-enrichment/running-faqs/is-there-any-science-to-support-crossfit-endurance/, Accessed on 26 February 2013
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