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High Intensity Interval Training

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[[File:Sprinter.jpg|right|thumb|400px|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, high periods of very intense cardiovascular exercise separated by lower intensity intervalsrecoveries. HIIT has been shown to improve both anaerobic and aerobic fitness capacity in trained athletes<ref>http://jp.physoc.org/content/575/3/901.short</ref>. It is one of the most efficient work outs in terms of improvement for time committeduntrained and moderately active individuals more quickly than Continuous Moderate Exercise, as well as being a lot 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 funtraining for endurance races. ==The Tabata Workout=What is HIIT?={{Main|Tabata}}The Tabata workout High Intensity Interval Training is 8x (20 seconds maximum effort with a form of [[Introduction to Interval Training| Interval Training]] using short intervals of 10 seconds recovery) for a four minute workoutto 5 minutes at an intensity at or above 90% [[VO2max|V̇O<refsub>http:2<//www.ncbi.nlm.nih.gov/pubmed/8897392sub>max]]<ref name="Boutcher2011"/ref>. Before starting the Tabata it High Intensity Interval Training, abbreviated to HIIT or HIT, is important to warm up thoroughly as this work outs a lot sometimes called High-Intensity Intermittent Exercise<ref name="Trapp-2008"/> or Sprint Training<ref name="Gibala-2006"/>.=HIIT Recommendations=Below are my recommendations based on my interpretation of stress on the bodyavailable evidence. The 'maximum effort' nature of the Tabata intervals creates significant risk These recommendations for injuryincorporating HIIT in your training depend on your current fitness goals. I would strongly suggest that you start doing the Tabata structure* For sedentary people, but instead HIIT is probably more effective in building initial fitness than Continuous Moderate Exercise. Three sessions per week of doing the 20 seconds 'all out', do them as comfortably hard. Over the course of a few weeks, build up to doing them as fast as you can. Another alternative is to do the workout [[#Wingate| Wingate]] HIIT on a stationary bike, riding out of the saddle to use should provide an improvement in fitness for a modest time commitment. Using [[#WinTab| WinTab]] style HIIT may produce similar muscles benefits for a lower time commitment. * For people looking to runninglose weight, but without the increased range HIIT will probably produce a greater reduction in body fat than Continuous Moderate Exercise. Three sessions per week of motion required by this level of intensityWingate HIIT on a stationary bike should help with weight loss and appetite control. ==The Little HIIT==A variant could be combined with other forms of exercise on the Tabata workout is the Little other days, which may further improve weight loss. (HIIT, named after Jonathan Little, one of the researchers<ref>http://studio4romtechprobably more effective than Continuous Moderate Exercise at improving insulin sensitivity.com/PDF%20links/McMasters_Study)* Recreationally active people looking for rounded fitness may benefit from including HIIT in their overall training program.pdf</ref>. The Little Adding 1-3 sessions per week of Wingate or WinTab HIIT uses 4 or 6 repeats 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 30 seconds 'all out' their training load with a 4 minute recovery after each intervalcombination of both traditional HIIT and shorter Wingate or WinTab style HIIT. ==Benefits==Up to one traditional HIIT or 1-3 shorter HIIT has been shown sessions could be included in a weekly training routine. Care should be taken to improve increase [[VO2maxTRIMP| Training Load]], mitochondrial activity slowly with the additional HIIT and performance in cycling time trialstry 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 also been shown to shift muscle fiber types from type IIb (a lower injury risk, but the additional benefits of outdoor running may outweigh the additional injury risk. However, the fast twitch) paces of the shorter HIIT should be introduced gradually, building up the pace over a number of workouts. * There is no direct evidence to type I (endurance)<ref>http://wwwindicate if HIIT will help athletes focused on improving their performance in events lasting longer than an hour.springerlink.com/content/1137px7x66667132/</ref> with type IIa unchangedHowever, it seems reasonable that HIIT would provide some benefits. ==Caveats==There are some caveats to Including 1 or 2 Wingate or WinTab HIIT sessions per week may be aware of with HIIT* It is remarkably easy appropriate. As noted in the prior bullet point for shorter duration athletes, care should be taken to get injured monitor [[TRIMP| Training Load]] and [[Training Monotony]]. As with running HIIT unless care is take to build up athletes focusing on events lasting less than an hour, the intensity over time. * HIIT stationary bike has shown to provide similar the lowest injury risk, but there may be benefits to other training modes. However, athletes competing in longer periods (90-120 minutes) of steady state exercise. I duration events typically don't have not found any studies showing the effect same need for the very high paces that are sometimes seen at the end of adding HIIT to an existing training programshorter events.* The changes with There is no evidence to suggest that HIIT include an increase in can be used to replace Continuous Moderate Exercise such as the size Long Run that is a core part of type I muscle fibers, whereas endurance training often results in smaller type I fibers that are more efficient. <ref>http://www=Types of HIIT=There are various different protocols for performing HIIT.springerlinkWhile the Tabata is probably the most widely recognized name in HIIT, it is one of the least studied and the least used.com/content/1137px7x66667132/</ref>* If the rest periods are long enough (15==Tabata==The Tabata workout is one of the best known protocols for HIIT and consists of 7-8 repeats of 20 minutes), then the training produces adaptations to sprinting rather then endurance.seconds at 170% of [[VO2max|V̇O<refsub>http://onlinelibrary.wiley.com/doi2</sub>max]] with 10seconds rest.1111/jThe number of repetitions is defined by how long the required intensity can be maintained.1748An athlete should be able to complete 7-1716.19908 intervals; if 9 can be performed, the intensity is increased.tb09010However, few people actually follow the Tabata protocol because it requires specialist equipment to measure [[VO2max|V̇O₂max]], then calculate 1.x/abstract7x the [[VO2max|V̇O<sub>2</refsub>=max]] workload that should be used. In practice, most people do what I call the WinTab workout (see below). =HIIT on a Treadmill=Wingate==This style of HIIT can not reasonably be done on a treadmill. This is partly because based around the intervals are very shortWingate test, with a dramatic change in pace between interval which is used to measure peak anaerobic power and recovery, so a treadmill acceleration becomes a problemanaerobic capacity<ref name="Vandewalle-1987"/>. The other issue is that Wingate HIIT uses 30 seconds of 'all out' is not a pace you can program into a treadmillintensity, followed by ~4 minutes of recovery, repeated 4-6 times.  == See Also WinTab (Tabata style Wingate)==* Most athletes that use the Tabata workout do not use the 170% [[Introduction to Workout TypesVO2max|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 [[Introduction to Interval TrainingWarmup]] =), rather than the variable number of repetitions of the original Tabata protocol.=References=Traditional Anaerobic Intervals==<referencesHigh 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<ref name="JD"/>, which is generally close to 100% [[VO2max|V̇O₂max]]. The 'R' workouts are 12-40 repeats of 30-60 seconds with 1-4 min rests<ref name="JD-P132"/>. 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<ref name="JD-P132"/>. =HIIT Training Mode=There are various ways that HIIT could be performed, each with their own pros and cons.{| class="wikitable"! 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<ref name="active.com-hills"/>).* 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 [[Best Running Watch| 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.|}=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 ([[VO2max|V̇O₂max]]). For each level, the 5K and marathon times are given, along with the pace that corresponds to 90%, 100% and 170% of [[VO2max|V̇O₂max]]. {| class="wikitable"! [[VO2max|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|}=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. ==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. {| class="wikitable"! Study! Subjects! Study length! Protocol! Outcome! Best Result! Notes|-| rowspan="4"| Helgerud-2007<ref name="Helgerud-2007"/>| rowspan="4"| Moderately trained([[VO2max|V̇O₂max]] 51-55)| rowspan="4"| 3 days/week8 weeks| '''Short HIIT'''47x 15 seconds at 90-95% [[Maximum Heart Rate|HR_max]] + 15 seconds at 70% [[Maximum Heart Rate|HR_max]] | Raised [[VO2max|V̇O₂max]] 7.2%| rowspan="4"| Short HIIT| rowspan="4"| All groups improved economy, with no differences, and Lactate Threshold unchanged as a percentage of [[VO2max|V̇O₂max]]|-| '''Long HIIT'''4x 4 min, 90-95% [[Maximum Heart Rate|HR_max]] + 3 min at 70%max| Raised [[VO2max|V̇O₂max]] 5.5%|-| '''Lactate threshold run'''24 min at 85% [[Maximum Heart Rate|HR_max]] | [[VO2max|V̇O₂max]] unchanged|-| '''Long Slow Distance'''45 minutes at 70% [[Maximum Heart Rate|HR_max]]| [[VO2max|V̇O₂max]] unchanged|-| rowspan="2"| TjonnaLee-2008<ref name="TjonnaLee2008"/>| rowspan="2"| Untrained, metabolic syndrome patients| rowspan="2"| 3 days/week16 weeks| '''HIIT'''4x 4 min at 90% [[Maximum Heart Rate|HR_max]] + 3 min 70% [[Maximum Heart Rate|HR_max]]total 40 min, | Raised [[VO2max|V̇O₂max]] 36%| rowspan="2"| HIIT| rowspan="2"| Same calories burned in each groupBoth groups had an equal reduction in body weight and blood pressure|-| '''Continuous Moderate Exercise'''47 min at 70% [[Maximum Heart Rate|HR_max]] | Raised [[VO2max|V̇O₂max]] 16%|-| rowspan="2"| Gibala-2006<ref name="Gibala-2006"/> | rowspan="2"| Recreationally active| rowspan="2"| 2 weeks| '''HIIT'''4-6x 30 seconds 'all out' + 4 min recoveryTotals for two weeks, 135 minutes and 950 Kj| rowspan="2"| Same improvement in laboratory time trials| rowspan="2"| HIIT| rowspan="2"| Same improvement, but only 22% of the time commitment|-| '''Continuous Moderate Exercise'''90-120 min at 65% [[VO2max|V̇O₂peak]]Totals for two weeks, 630 minutes and 6500 Kj|-| rowspan="2"| Gorostiaga-1991<ref name="Gorostiaga-1991"/> | rowspan="2"| Sedentary| rowspan="2"| 3 days/week8 weeks| '''HIIT'''30x 30 sec @ 100% [[VO2max|V̇O₂max]] + 30 sec rest| Raised [[VO2max|V̇O₂max]] 9-16%No change in blood lactate during continuous exercise | rowspan="2"| HIIT| rowspan="2"| Same average work in each group|-| '''Continuous Moderate Exercise'''30 minutes at 50% [[VO2max|V̇O₂max]]| Raised [[VO2max|V̇O₂max]] 5-7%Reduced blood lactate during continuous exercise by nearly 50%|-| rowspan="3"| Franch-1998<ref name="Franch-1998"/>| rowspan="3"| 36 recreational runners| rowspan="3"| 3 days/week at high intensityPlus 3 runs/week <= 65% [[Maximum Heart Rate|HR_max]]6 weeks| '''Short HIIT'''30-40x 15 sec run, 15 sec restAvg ~3.0 Km/workout92% [[Maximum Heart Rate|HR_max]]| Time to exhaustion increased 65%Running economy improved 0.9%| rowspan="3"| Continuous High Intensity| rowspan="3"| 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 restAvg ~5.6 Km/workout94% [[Maximum Heart Rate|HR_max]]| Time to exhaustion increased 67%Running economy improved 3.0%|-| '''Continuous High Intensity'''20-30 minutesAvg ~6.4 Km/workout93% [[Maximum Heart Rate|HR_max]]| Time to exhaustion increased 94%Running economy improved 3.1%|-| rowspan="2"| BurgomasterHowarth-2007<ref name="BurgomasterHowarth2007"/>| rowspan="2"| 20 Untrained| rowspan="2"| HIIT 3x weekContinuous 5x week6 weeks| '''HIIT'''4-6x 30 seconds 'all out', 4.5 min rest1.5 hours/week~225 Kj/week| rowspan="2"| Both increased [[VO2max|V̇O₂peak]] by ~5%| rowspan="2"| HIIT| rowspan="2"| 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% [[VO2max|V̇O₂peak]]4.5 hours/week2250 Kj/week|-| rowspan="2"| Trapp-2008<ref name="Trapp-2008"/>| rowspan="2"| 34 sedentary women| rowspan="2"| 45 workouts over 15 weeks| '''HIIT'''60x 8 seconds 'all out', 12 seconds rest (5 min [[Warmup]], 20 min conditioning, 5 min cooldown)| Increased [[VO2max|V̇O₂peak]] 24%5 pound/2.5 Kg reduction in body fatSignificant 31% reduction in fasting insulinSignificant reduction in [http://en.wikipedia.org/wiki/Leptin Leptin]| rowspan="2"| HIIT| rowspan="2"| 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% [[VO2max|V̇O₂peak]]| Increased [[VO2max|V̇O₂peak]] 19%1 pound/0.5 Kg gain in body fatNon-significant 9% reduction in fasting insulinNo change in [http://en.wikipedia.org/wiki/Leptin Leptin]|-| rowspan="2"| Tabata-1996<ref name="Tabata-1996"/>| rowspan="2"| 14 varsity level collage athletes ([[VO2max|V̇O₂max]] ~50)| rowspan="2"| 5 days/week6 weeks| '''HIIT'''4 days/week 7-8x (30 seconds at 170% [[VO2max|V̇O₂max]] + 10 seconds rest)1 day/week 30 min at 70% [[VO2max|V̇O₂max]] + 4x (30 seconds at 170% [[VO2max|V̇O₂max]] + 10 seconds rest)| Raised [[VO2max|V̇O₂max]] by 14.5%Increased anaerobic capacity by 28%| rowspan="2"| HIIT| rowspan="2"| HIIT produced a greater improvement in [[VO2max|V̇O₂max]] for far less time commitment|-| '''Continuous Moderate Exercise'''60 minutes at 70% [[VO2max|V̇O₂max]]| Raised [[VO2max|V̇O₂max]] by 9.5%No change in anaerobic capacity |}==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% [[VO2max|V̇O₂max]] from 25 to 51 minutes, despite no change in [[VO2max|V̇O₂max]]<ref name="Burgomaster-2005"/>, a remarkable improvement. In another study, the combination of Continuous Moderate Exercise and moderate intensity intervals (60-70% [[VO2max|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<ref name="Tremblay-1994"/>. 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 [[VO2max|V̇O₂max]] by 44%, as well as improved running endurance, with some subjects ending up with a [[VO2max|V̇O₂max]] exceeding 60 ml/kg per min, which is remarkably high for 10 weeks of training<ref name="Hickson-1977"/>. ==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<ref name="Laursen-1-2002"/>. This is backed up by studies of some of the great endurance athletes, where higher training mileage produced worse rather than better performance<ref name="elitemileage"/>. 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"<ref name="LoR-P477"/>. Of course this is not universally true, and Mike Morton, set the US record holder for 24 hour while training 140-150 miles/week<ref name="militarytimes.com"/>. 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<ref name="Lindsay-1996"/><ref name="Westgarth-Taylor-1997"/>* 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<ref name="Stepto-1999"/>. 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. {| class="wikitable"! 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 [[vVO2max|T_lim]] , where [[vVO2max|T_lim]] is the time to exhaustion at 100% [[VO2max|V̇O₂max]]<ref name="Laursen-1-2002"/>.* 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 [[VO2max|V̇O₂max]] by 4.9% (61 to 64)<ref name="Smith-1999"/>. The HIIT training consisted of 2 sessions per week of 6 intervals at 100% [[VO2max|V̇O₂max]] with time varying between 60-75% [[vVO2max|T_lim]], plus one weekly run of 30 min at 60% v[[VO2max|V̇O₂max]]. For these runners, [[vVO2max|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% [[VO2max|V̇O₂max]] for either 6x 60% [[vVO2max|T_lim]] (133 sec) or 5x 70% (154 sec) [[vVO2max|T_lim]], resting for twice the interval time. Their 3K time improved by 17.6 sec (60% [[vVO2max|T_lim]]) or 6.3 sec (70% [[vVO2max|T_lim]]), but there was no change in their 5K time<ref name="Smith-2003"/>.* 41 elite ([[VO2max|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<ref name="Laursen-3-2002"/>. Note that groups 1 and 2 vary only in their rest time, which is based on heart rate dropping to 65% of [[Maximum Heart Rate|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 [[VO2max|V̇O₂max]] which was not statistically different between group 3 and the controls. {| class="wikitable"! Group! Intended number of intervals! Interval Duration! Total work time (min)! Intensity (% [[VO2max|V̇O₂max]])! Rest ! Total time! [[VO2max|V̇O₂max]] change! 40K Time Trial Speed improvement|-| 1| 8| 60% [[vVO2max|T_lim]](~150 sec)| 20| 100%| 120% [[vVO2max|T_lim]] (~290 sec)| 58 min| 5.2%| 5.2%|-| 2| 8| 60% [[vVO2max|T_lim]](~150 sec)| 20| 100%| 65% [[Maximum Heart Rate|HR_max]] (~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 [[VO2max|V̇O₂max]] + 120 sec recovery) that improved peak power by 4% but had no change in [[VO2max|V̇O₂max]]<ref name="Laursen-2-2002"/>.==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 [[VO2max|V̇O₂max]]. While [[VO2max|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.=Crossfit Endurance=Crossfit Endurance is a training approach that reduces the normal endurance training volumes while increasing the training intensity<ref name="www.crossfitendurance.com-about"/>. 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<ref name="crossfitmarathon"/>. While there are some testimonials to the Crossfit Endurance methodology<ref name="www.crossfitendurance.com-test"/>, their approach is controversial<ref name="SoRCf"/>. 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<ref name="metamorphitness.wordpress.com"/>. 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. =References=<references><ref name="metamorphitness.wordpress.com"> 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</ref><ref name="SoRCf"> Science of Running: Crossfit endurance, Tabata sprints, and why people just don&#8217;t get it, http://www.scienceofrunning.com/2012/01/crossfit-endurance-tabata-sprints-and.html, Accessed on 26 February 2013</ref><ref name="www.crossfitendurance.com-test"> Testimonials, http://www.crossfitendurance.com/testimonials, Accessed on 26 February 2013</ref><ref name="www.crossfitendurance.com-about"> About Crossfit Endurance, http://www.crossfitendurance.com/whatiscfe, Accessed on 26 February 2013</ref><ref name="crossfitmarathon"> 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</ref><ref name="Tabata-1996">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 [http://www.ncbi.nlm.nih.gov/pubmed/8897392 8897392]</ref><ref name="Smith-2003"> 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 [http://dx.doi.org/10.1007/s00421-003-0806-6 10.1007/s00421-003-0806-6], PMID [http://www.ncbi.nlm.nih.gov/pubmed/12736843 12736843]</ref><ref name="Smith-1999"> TP. Smith, LR. McNaughton, KJ. 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