Changes

There are three main variable several variables that shape a HIIT workout<ref name="BuchheitLaursen2013"/>. * '''Work 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|VOV̇O₂max]]. The classic Tabata workout used 1.7x the work at [[VO2max|VOV̇O₂max]], though many implementations of this workout simply use "all out."* '''Duration'''. Given intensities at or above Some consider that the threshold of HIIT to be 90% of the effort of [[VO2max|VOV̇O₂max]]<ref name="Billat-2001"/><ref name="Midgley-2006"/>. In fact, 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 some have suggested that the goal of HIIT is to mimic some of maximize the characteristics of a lower intensity, longer duration interval. At the other extremetime above 90% [[VO2max|V̇O₂max]]<ref name="BuchheitLaursen2013"/>. Work intensity is nearly always constant, though there is no reason why the recovery work for a given interval can be long enough to ensure nearly complete recoverya ramp, typically taking several minuteseither increasing or decreasing in intensity during the interval. The recovery intensity can be activeLikewise, but the effort is nearly always fairly lowintensity could vary between intervals, either incrementing or decrementing.=HIIT Comparisons on Untrained * '''Work Duration'''. Given intensities at or Moderately Active Subjects=The table below looks at studies that have compared HIIT with other types of trainingabove [[VO2max| V̇O₂max]], the duration needs to be quite short, and it's often Continuous Moderate Exercise (CME)30 seconds or less. These studies on untrained or moderately trained subjects generally show a greater improvement in fitness measure compared with other forms of Work duration is typically constant throughout the interval trainingsession, or similar improvements for far less training timebut there's no reason why it couldn't change. {{:* '''Recovery Intensity'''. The Science of High Intensity Interval Training-table}}==Aerobic High-Intensity Intervals Improve VO2Max More Than Moderate Training==This study<ref name="Helgerud-2007"/> was on 40 male university studentsrecovery intensity can be active, but the effort is nearly always fairly low. The work done during the recovery. Can actually help metabolize lactate, all physically active and with [[VO2max|VO₂max]] of 55-60improve recovery in some ways.* '''Recovery Duration'''. The recovery period can be extremely short, which is translates tends to marathon times of 2:55 to 2:43, so they're pretty fit. The four running based training interventions were designed to have mimic some of the same amount characteristics of total worka lower intensity, which makes this study a little unusual as often HIIT requires far less work than other approacheslonger duration interval. Each program included 3 workouts per week and lasted for 8 weeks. The training is described in At the table aboveother extreme, and all performed on a treadmill at 5.3% incline. I noticed that the LSD is somewhat higher intensity 70% [[Maximum Heart Rate]]recovery can be long enough to ensure nearly complete recovery, and shorter 45 min than Itypically taking several minutes. * '''Number of Intervals'''d expect for typical LSD training. The [[Lactate Threshold]] was defined as 1.5 mmol/l above restingThe number of intervals used can vary dramatically, which is slightly oddwith one study looking at a single interval, but no worse than most protocols through to studies that don't use several dozen intervals.Other variables include the gold standard possibility of Maximum Lactate Steady State. The LSD and LT runs decreased the speed repeating a series of the treadmill as the heart rate rose due intervals with a longer break. For instance, it will be possible to drift. The short interval protocol was based around 15 seconds at 90do something like 6x(30s+30s recovery), then take a two-95% [[Maximum Heart Rate]] with 15 seconds minute 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 comparisonthen repeat the six intervals again. There are also macro variables, such as the four repeats frequency of 4 minutes with 3-minute recoveries is rather more mainstream. All four protocols burned similar levels of oxygenperforming the HIIT workouts.[[File:Helgerud-2007-HR.jpg|center|thumb|600px|Heart rate ==Naming Convention==I've not found a naming convention for the four interventionsHIIT, top left so I've started to bottom right: LSD, Lactate Threshold, 47x15+15, 4x4+3.use HIIT-[d][r]The results were that [i]. In my convention, [VO2max|VO₂max]] went down fractionally d] is duration, with S for LSD Short, typically 30 seconds or less, and up fractionally L is for Lactate ThresholdLong, though neither was typically a significant change from baselineminute or longer. The two interval training approaches raised Then [[VO2max|VO₂max]r] is the recovery, with no significant differenceC for Complete, though the 4x4 was slightly better which is typically several minutes of recovery, and I is for Incomplete, typically less than the 47x15duration of the interval itself. [The [Running Economyi]] and [for intensity is based on the intensity of [Lactate Threshold[VO2max| V̇O₂max]] were unchanged for all groups. [[File:Helgerud-2007-Vo2max, so the Tabata 170% would be x170.jpg|center|thumb|300pxIf only the percent [[Maximum Heart Rate|HR_max]], that is used instead. Where 'all out'is specified, I'Conclusionve used xAO, as the ratio of Wingate 'all out'': this study suggests that high intensity training can improve the aerobic capacity of relatively fit subjects, while LSD and lactate threshold training is ineffectivepower to [[VO2max| V̇O₂max]] appears to be 2-4x. However, Some examples from the structure of the short intervals studies reverenced here would be:* HIIT-SIx90 is rather unusual, and atypical, and I'm not sure I would consider either protocol truly "HIIT".==Aerobic Interval Training Versus Continuous Moderate Exercise as a Treatment for the Metabolic Syndrome==This is a similar study15 seconds at 90-95% [[Maximum Heart Rate|HR<sub>max<ref name="TjonnaLee2008"/sub> to the one above, both from "Norwegian University of Science and Technology", though the researchers appear different]] + 15 seconds recoveries. The subjects are certainly different, as they are 32 patients with metabolic syndrome* HIIT-SCxOA is 30 seconds 'all out' + 4 min recovery.* HIIT-LCx90 is 4 min run, average 2 min rest at 94% [[VO2maxMaximum Heart Rate|VOHR_2maxmax]] is 34* A classic Tabata would be HIIT-SIx170A more precise definition could use a convention based on QWKCODEs used by Golden Cheetah, which translates to about a 4:20 marathonbut allowing for percentages. This study used just two training programs; 47 minutes So "6x30s@90%r30s@50%" would be 30 seconds at 7090% of [[Maximum Heart Rate]] or four intervals of 4 minutes with 30 second recovery at 50%. Using power at 70% of [[Maximum Heart Rate]] with 3-minute recoveries. Each program included 3 workouts per week and lasted for 16 weeksVO2max|V̇O₂max]] would be most precise, consisting though many studies use percentages of walking/running on an incline treadmill[[Maximum Heart Rate]]. ==Typical Styles of HIIT==There are several styles of HIIT. * The intervals resulted in a greater improvement in [[VO2max|VO₂max]]first, epitomized by Tabata is HIIT with short, and better mitigation of the risk factors associated with metabolic syndrome. <br/>'''Conclusion''': incomplete recovery periods. In this extends style, the previous study's finding to less fit subjects who have medical issuesrecovery periods are often 50-100% the duration of the interval, and the heart rate for this style of HIIT will often appear close to steady state. ==Short-term sprint interval versus * The more traditional endurance training===HIIT Studies on Untrained or Moderately Active Subjects without Controls=While studies that compare HIIT with other forms style of interval training are the most usefulis long, there are a few other studies on untrained or moderately active people that are noteworthy. For instancecomplete recoveries, six sessions which have recoveries of HIIT over two weeks doubled several minutes, allowing the endurance of untrained subjects at 80% [[VO2max|V̇O₂max]] from 25 heart rate to return to 51 minutesa much lower level and producing a distinct saw-toothed heart rate graph. In practice, despite no change in [[VO2max|V̇O₂max]]<ref name=recovery is not actually "Burgomaster-2005complete"/>, a remarkable improvementbut the athlete should feel reasonably ready to perform at nearly the same level. In another study, * A third style is with the combination short intervals of Continuous Moderate Exercise and moderate Tabata, but with complete recovery periods. This style allows for greater intensity intervals (60-70% [[VO2max|V̇O₂max]]) reduced body fat by 15%to be achieved for the short periods. =Optimizing High Intensity Intervals =There is remarkably little scientific basis for optimizing HIIT. Different studies use various combinations of intensity, duration, which was nine times more than Continuous Moderate Exercise aloneand recovery, even though and I found no attempt at finding the Continuous Moderate Exercise burned over twice the calories<ref name="Tremblay-1994"/>optimal combination. Another study also used Below you'll find a combination of HIIT on 3 dayfew studies that will do some coarse comparisons, such as 15sec/week plus running as far as possible in 40 15sec compared with 4 min on another 3 days/week 4min, resulting in an increase in but nothing more detailed. One hypothesis is that the intensity should be above the intensity that it generates [[VO2max|V̇O₂max]] by 44%, as well as improved running endurance, with some subjects ending up with a [[VO2max|V̇O<sub>2<<ref name="Laursen-1-2002"/sub>max]] exceeding 60 ml/kg per min, which . This is remarkably high for 10 weeks of trainingbased on the observation<ref name="Hickson-1977Bassett2000"/>. =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[[VO2max|V̇O<sub>2<ref name="Laursen-1-2002"/sub>. This max]] is backed up limited by studies of some the ability of the great endurance athletes, where higher training mileage produced worse rather than better performance<ref name="elitemileage"/>. In the Lore of Runningcardiovascular system to deliver oxygen to the working muscles. This seems to be a remarkably tenuous basis, Tim Noakes said that elite runners perform best "when they train between 75-125 miles (120-200 km) per week, with an increasing likelihood but there's not much else to go on so far. There is some evidence that they will perform indifferently when they if you want to train more than 125 miles (200 km) per week"at or above [[VO2max|V̇O<sub>2<ref name="LoR-P477"/sub>. Of course this is not universally truemax]], and Mike Morton, set then intermittent training allows athletes to maintain the US record holder for 24 hour while training 140-150 miles/week[[VO2max|V̇O<sub>2<ref name="militarytimes.com"/sub>. Howevermax]] intensity for much longer (3x) than continuous exercise<ref name="Billat-2000"/>. If you accept this approach to intensity, then the evaluation duration 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 the intervals can be defined in highly trained athletes as they are typically already performing large volumes terms of Continuous Moderate Exercise. Instead[[vVO2max|T_lim]], 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"where [[vVO2max|T_lim<ref name="Westgarth-Taylor-1997"/>* A study of elite cyclists used various HIIT workouts as shown in ]] is the table below, with the best results seen group 4 or group 1<ref name="Stepto-1999"/>. Group 4 trained time to exhaustion at 85100% peak power, which corresponds to the intensity normally seen in the 40K time trial, which takes ~60 minutes for an elite cyclist[[VO2max|V̇O2max]]. Not surprisingly, (Obviously you can't train for longer than this intensity is commonly used for cyclists training for 40K time trials. However, the higher intensity ) Examples 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 interval structure that use [[vVO2max|T_lim]] have durations of 50-75% of [[vVO2max|T_lim]], and recovery periods are commonly the possibility that same as the benefits of the different intensities might be combinedinterval, or twice the interval duration<ref name="Laursen-1-2002"/>. Note It's been observed that there were only four athletes in each group, and responses tended highly trained runners take at least 60% of [[vVO2max|T_lim]] to vary, so caution reach [[VO2max|V̇O₂max]] <ref name="Hill-1997"/>. This has been taken as an indication that intervals should be used at least that long, but of course that observation only holds true for a single bout, not a repeated set of intervals. In fact, there's some evidence that exercise above [[Lactate Threshold]] but below the intensity [[VO2max|V̇O₂max]] can increase oxygen consumption to the [[VO2max|V̇O₂max]] level<ref name="Lucia2000"/><ref name="Billat-1999"/>. (This is often referred to as the |V̇O₂ slow component.) One study found that 30 second intervals with 30 second recoveries allows for more time at or above 95% [[VO2max|V̇O2max]] than 3 minute intervals with 3 minute recoveries<ref name="ZunigaBerg2011"/>. ==Effects of different interval-training programs on cycling time-trial performance (Stepto-1999)==This is one of the few studies that compares different types of interval training<ref name="Stepto-1999"/>. Unfortunately, this study only had 20 cyclists, divided into five groups, which produced a group size of only four athletes (one cyclist dropped out giving one group only three athletes.) The study varies the intensity and duration inversely from 175%/0.5 minute to 80%/8 minutes. The study measured 40Km time trial performance, peak power output, and Sprint performance. {{:The Science of High Intensity Interval Training-table-Stepto1999}}Three of the protocols improved the time trial performance, but there was a lot of variability between the individual athletes. The study attempts to link the different protocols using a cubic trend, which seems a little bizarre to me. The intervals above [[VO2max|V̇O2max]] of group 1 produced results that varied from no improvement through to more than 4% improvement in TT, while the slightly longer [[VO2max|V̇O2max]] intensity intervals of group 2 produced a little improvement in TT. It might be tempting to conclude that HIIT needs to be greater [[VO2max|V̇O₂max]], but this could easily be skewed by the small sample size. The longer intervals that are closer to a typical aerobic interval training session produce more consistent improvements in TT, but again, a small sample size makes it hard to be confident.[[File:Stepo1999.jpg|center|thumb|300px|]]==Time To Benefit==[[Modeling Human Performance]] is based on the premise that any training stress will produce a short-term impairment in performance, followed by a longer-term benefit. This is seen in every day training, where a hard training session results in degraded performance the next day. The time between the training stress and the benefit seems to vary based on multiple factors, including training status, type of training, and individuality. HIIT with endurance trained cyclists resulted in no improvement after two weeks, but it did after four weeks<ref name="Lindsay-1996"/>. A study of eight endurance trained competitive cyclists who had not performed any interval training for at least three months suggests the bulk of the improvement occurs within 12 days<ref name="Westgarth-TaylorHawley1997"/>. The training was 6-9x (5min @ 80% [[VO2max|V̇O₂max]] + 1 min recovery). This is not really intensive enough to be HIIT, and is closer to traditional aerobic intervals, so caution is needed in interpreting the results.

! GroupDays! Number of intervalsSessions! Interval duration (min)! Total work time (min)! Intensity (% peak power)! Rest (min)! Total Time! Improvement in 40K Time Trial Speed! Improvement in Peak Power

| 1Baseline| 12| 0.5| 6| 175%| 4.5| 60 min| 2.0%| 0.5%404

| 1| 12| 100%| 4.0| 60 min| 0.0%| 0.5%419

| 4| 32| 85%| 1.5| 44 min| 2.5%| 2.0%421

| 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" style="margin-left: auto; margin-right: auto; border: none;"! 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

| 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%424

* Elite ==Training Frequency==Most studies seem to train their subjects 3-4 times per week, and while the protocol seems intuitively reasonable, there's little supporting evidence. A study of 10 healthy volunteers compared to training protocols that were identical other than the frequency of training<ref name="Parra-2000"/>. Both protocols used 30 seconds of maximal cycling with 12-minute recovery periods (unusually long.) The number of repetitions was increased during the study as the subjects became fitter. In one group, the subjects trained every day, while the other group had to day rest periods between each training session. The subjects without rest days did not improve either average or peak power during a 30-second Sprint test, while the subjects that did have rest days improved both of values. This is weak evidence that rest days between HIIT sessions are good idea.==Recovery Duration==Most studies tend to use a simple ratio of interval to recovery period of 2:1, 1:1, 1:2. The famous Tabata compared his usual regime of 6-7x (20seconds @ 170% [[VO2max|V̇O₂max]] + 10 seconds recovery) with 4-5x(30 seconds @ 200% [[VO2max|V̇O₂max]] + 120 seconds recovery) <ref name="Tabata-1997"/>. Not surprisingly, the shorter recovery times taxed both aerobic and anaerobic systems far more than the longer recovery times, but there was no evaluation of any performance benefit from the two protocols. A study of seven physical education students tested recovery periods of 30, 60, & 120 seconds between fifteen 40 m sprints<ref name="Balsom-1992"/>. The Sprint times were only ~5-6 seconds long, and for the 120 seconds recovery, the Sprint times remained fairly constant, for the 60 second recovery, the lost three sprints were slower, and for the 30 second recovery there was a progressive slow down for each interval. Blood lactate levels were surprisingly similar for all recovery periods, only becoming different after the session had completed, with the longer recovery is having lower blood lactate that dropped more quickly. One study found that not surprisingly the difficulty (RPE) varied dramatically with the recovery duration, with the shorter recoveries being harder<ref name="ZavorskyMontgomery1998"/>.=Recovery Intensity=Most studies use active recovery, where the athlete continues to exercise between intervals. This activity may speed recovery by metabolizing the lactic acid faster than complete rest<ref name="Belcastro-1975"/>, but this seems to be no evidence comparing different levels of recovery intensity.=HIIT Comparisons on Untrained or Moderately Active Subjects=This section 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. By comparing two different types of exercise, we get the most useful information. {{:The Science of High Intensity Interval Training-table}}==Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max (Tabata-1996)==This study<ref name="Tabata-1996"/> is arguably the origin of HIIT, and is the most famous name, [[Tabata]]. Izumu Tabata was the coach that tested a training protocol and compared it with the more conventional continuous exercise. The study is small, with just 14 male physical education students divided into two groups, and it's reasonably short at 5 days/week for only six weeks. The students had a [[VO2max|V̇O₂max]] of ~50, which would translate to a marathon time of about 3:10. (I have a more intuitive grasp of someone's fitness level from their hypothetical marathon time than their raw [[VO2max|V̇O₂max]].) The small number of subjects weren't quite as closely matched as I would have liked, with the continuous exercise having a [[VO2max|V̇O₂max]] of ~53 and the HIIT group having ~48. Both training protocols used a stationary bike, and both protocols increased the training intensity to maintain the required percentage of [[VO2max|V̇O₂max]]. The continuous exercise protocol was 60 minutes at 70% [[VO2max|V̇O₂max]], and it raised [[VO2max|V̇O₂max]] by 9.5%. The study also used a measure of anaerobic capacity by evaluating the oxygen debt, and found no change for the continuous exercise protocol. The HIIT protocol used 7-8x repeats of 20 seconds at 170% [[VO2max|V̇O₂max]] + 10 seconds rest (HIIT-SIx170). It also included one day/week of 30 min at 70% [[VO2max|V̇O₂max]] + 4x (30 seconds at 170% [[VO2max|V̇O₂max]] + 10 seconds rest). It's unclear why there is this mixture of protocols for the HIIT. The HIIT included a 10-minute warmup at 50% [[VO2max|V̇O2max]]. The HIIT training raised [[VO2max|V̇O₂max]] by 14.5%, and increased anaerobic capacity by 28%.'''Conclusion''': This study suggests that HIIT-SIx170 can increase [[VO2max|V̇O₂max]] more than continuous moderate exercise, as well as improving anaerobic capacity in a way that doesn't occur with continuous moderate exercise.==Aerobic High-Intensity Intervals Improve VO2Max More Than Moderate Training (Helgerud-2007)==This study<ref name="Helgerud-2007"/> was on 40 male university students, all physically active and with [[VO2max| V̇O₂max]] 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 produced 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.[[File:Helgerud-2007-HR.jpg|center|thumb|600px|Heart rate for the four interventions, top left to bottom right: LSD, Lactate Threshold, 47x15+15, 4x4+3.]]The results were that [[VO2max| V̇O₂max]] 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| V̇O₂max]] with no significant difference, though the 4x4 was slightly better than the 47x15. [[Running Economy]] and [[Lactate Threshold]] were unchanged for all groups. [[File:Helgerud-2007-Vo2max.jpg|center|thumb|300px|]]'''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 would not classify the intensity as sufficient to quality as HIIT. ==Aerobic Interval Training Versus Continuous Moderate Exercise as a Treatment for the Metabolic Syndrome (TjonnaLee2008)==This is a similar study<ref name="TjonnaLee2008"/> 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| V̇O₂max]] 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| V̇O₂max]], and better mitigation of the risk factors associated with metabolic syndrome. <br/>'''Conclusion''': this extends the previous study's finding to less fit subjects who have medical issues. ==Short-term sprint interval versus traditional endurance training (Gibala-2006)==This small, short study<ref name="Gibala-2006"/> used a group of 16 active men, with [[VO2max| V̇O₂max]] of ~50, which is translates to about a 3:10 marathon time. They were divided into two groups, both groups training on a stationary bike six times over two weeks. The HIIT group did "all out" intervals of 30 seconds with 4-minute recoveries, repeated 4-6 times. The study noted that "all-out" was about 700 watts, which is quite intense. The endurance group did 90-120 minutes at 65% of [[VO2max| V̇O₂max]], which was noted at about 175 watts. Given the two groups had similar [[VO2max| V̇O₂max]] values, that means the HIIT group were exercising at 260% of the effort for [[VO2max| V̇O₂max]], far higher than the 170% of that Tabata used<ref name="Tabata-1996"/>. I'd classify the intervals as HIIT-SCx260. On average the HIIT exercised for 135 minutes, burning ~230 Calories while the endurance group exercised for 630 minutes and burned ~1550 Calories. Both groups improved their time trail performance by similar amounts. The study looked at lots of factors, but the small group size made many of the differences non-statistical. [[File:Gibala-2006.jpg|center|thumb|300px|The changes in time trial for HIIT (SIT) and endurance (ET). ]]'''Conclusion''': The HIIT-SCx260 produced similar performance improvements for less than a quarter the time. ==Uniqueness of interval and continuous training at the same maintained exercise intensity (Gorostiaga-1991)==This is a small study<ref name="Gorostiaga-1991"/> of 12 subjects for 8 weeks, with an initial [[VO2max| V̇O₂max]] of ~36, which is translates to a 4:10 marathon. Half the subjects cycled for 30 minutes at 50% the effort of [[VO2max| V̇O₂max]], the other half did 30 seconds at 100% the effort for [[VO2max| V̇O₂max]] with 30 seconds recovery, repeated 30 times. This roughly equates to the same training stress for both groups. The interval training was short, Incomplete-recovery at 100%, or HIIT-SIx100. The HIIT group improved [[VO2max|V̇O₂max]] by 9-16% while the continuous training group improved by 5-7%. As fitness improved, the training load increased to maintain the same percentage of [[VO2max|V̇O₂max]]. Because of this, the training load in the HIIT group rose by 10% compared with 5% for the continuous training group. There were changes in [[Lactate]] levels after training, but these are tricky to interpret. Both groups had their Lactate levels checked during intermittent and continuous exercise, before training, and again after the training at both the same absolute workload and the same relative workload. I'm hesitant to draw any conclusions from the lactate levels as there are too many variables to consider. The HIIT training is slightly unusual, as 30 repetitions is far higher than most HIIT approaches.'''Conclusion''': The HIIT-SIx100 improved [[VO2max|V̇O₂max]] more than continuous exercise, but the training used more repetitions at a lower intensity than is typical of HIIT. ==Improved running economy following intensified training correlates with reduced ventilatory demands (Franch-1998)==This is a slightly larger study<ref name="Franch-1998"/> of 36 runners with a pre-training [[VO2max| V̇O₂max]] of ~55, which translates to a 2:55 marathon. All are established recreational runners, and were divided into three groups. Four weeks before the test, the runners' training was evaluated and on average they ran for 2.2 hours/week at about 65% of max heart rate. The study then used three intense training runs per week for six weeks, plus 1-3 of their normal training runs per week. Three different intense training programs were used. Short HIIT was 30-40x 15 sec run with 15 sec rest (SIx90), Long HIIT was 4-6x 4 min run with 2 min rest (LCx90), and Distance Training (DT) was 20-30 minutes. The intensity and repetitions were designed to so the runners reached exhaustion, with average paces of 6:25 min/mile for DT, 5:49 for Long HIIT, and 4:43 for Short HIIT. My interpretation is that the DT training was well above Lactate Threshold, though it's hard to be sure from the details provided. The distance covered was 4miles/6.4Km for DT, 3.5miles/5.6Km for Long HIIT, 1.9miles/3Km for Short HIIT. While the average training load was 2.7 hours/week, it varied between 1.8 and 5.2 hours, and it's not clear if the distribution was even between the interventions. The average heart rate was reported as 92-94% of max HR for all interventions. [[VO2max| V̇O₂max]] improved for all groups, with DT=5.9%, Long HIIT=6.0%, and Short HIIT=3.6%. The time to exhaustion increased dramatically, with DT=94%, Long HIIT=67%, and Short HIIT=65%. [Running Economy]] improved in both DT and Long HIIT, but not Short HIIT, while heart rate and lactate were comparably lower for all interventions. '''Conclusion''': This study indicates that a high volume (30-40) of short, moderately high intensity intervals is not as effective as either longer intervals or continuous running at a similar intensity. ==Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans (BurgomasterHowarth2007)==This is study<ref name="BurgomasterHowarth2007"/> of 20 subjects with a pre-training [[VO2max| V̇O₂max]] of ~41, which translates to a 3:45 marathon. The training consisted of 3 cycling workouts per week for six weeks. The Endurance group hich cycled at 65% [[VO2max| V̇O₂max]] for an hour, while the HIIT group cycled did 4-6 repeats of 30 seconds "all out" with 4.5 minute recoveries. The "all out" intensity was about 500w, which equates to about 220% of the effort for [[VO2max| V̇O₂max]], so this is HIIT-SCx220. The training effort was 1.5 hours/week for the HIIT and 4.5 hours/week for the endurance, and the Calories burned were roughly ten times higher in the endurance group. Both groups improved [[VO2max| V̇O₂max]] by similar amounts (41 to 45), and had similar changes in enzyme activity. '''Conclusion''': Similar [[VO2max| V̇O₂max]] improvement for far less time with HIIT than continuous training. ==Low- and High-Volume of Intensive Endurance Training Significantly Improves Maximal Oxygen Uptake after 10-Weeks of Training in Healthy Men (EarnestTjønna2013)==This study<ref name="EarnestTjønna2013"/> was to evaluate the incremental benefits of additional repetitions in overweight, sedentary men. The subjects were 26 healthy overweight men (BMI 25-30), who had not exercised regularly for at least two years. The [[VO2max|V̇O₂max]] for the two groups was a little different, with the single repetition group having a [[VO2max|V̇O2max]] of 40 while the four-repetition group was ~45. That translates to marathon time of 3:50 and 3:28 respectively. The four-repetition group was also about 20Lb/10kg lighter. These differences could influence the outcome. The study had the subjects exercise on a treadmill for 3 days/week for 10 weeks. After the training, both groups improved, but the study provided no statistical analysis as to which differences were statistically significant. The four-repetition group improved [[VO2max|V̇O₂max]] by 13% and work economy by 13%, while the single repetition group improved by 10% and 14% respectively. There were drops in blood pressure, but without statistical significance calculations it's hard to interpret those drops.'''Conclusion''': A single repetition of four minutes high intensity produced broadly similar improvements in fitness as a single repetition for sedentary, overweight, but otherwise healthy men.=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. ==Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans (Burgomaster-2005)==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. 16 subjects were used with 8 acting as controls, and their [[VO2max|V̇O2max]] was ~45 (3:30 marathon equivalent.) Improvements in endurance aren't always seen with HIIT (or maybe just not looked for). The HIIT also increased peak power and glycogen storage.==Linear increase in aerobic power induced by a strenuous program of endurance exercise (Hickson-1977)==The 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 (2:43 marathon equivalent), 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. ==Improved athletic performance in highly trained cyclists after interval training (Lindsay-1996)==HIIT improved peak power output and 40 Km time trial in elite cyclists<ref name="Lindsay-1996"/>. The subjects were 12 competitive male cyclists who'd been training for at least four years, but had not performed any interval training in the last three months. Their average [[VO2max|V̇O₂max]] was 65 (2:33 marathon equivalent), and their power at [[VO2max|V̇O₂max]] was 416w. The HIIT used 6-8x(5 min @ 80% [[VO2max|V̇O₂max]] with 1 min at 100w recoveries.) The HIIT was performed over 6 sessions spread out over 4 weeks.==Metabolic and performance adaptations to interval training in endurance-trained cyclists (Westgarth-Taylor-1997)==This is study<ref name="Westgarth-Taylor-1997"/> is from the same university and has a common subset of researchers as the above study (Lindsay-1996). It's not clear if this study used a subset of the subjects above, but there are noteworthy similarities. Instead of 12 cyclists, this study used 8, with a similar fitness levels, and a similar HIIT protocol. Instead of 6-8 repeats, this study used 6-9, with 12 sessions over 6 weeks. The results are broadly similar to the previous study.==Effects of 4-wk training using Vmax/Tlim on VO2max and performance in athletes (Smith-1999)==Five 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"/>. That [[VO2max|V̇O2max]] improvement represents a marathon equivalent of 2:41 to 2:35.) 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.==Optimising high-intensity treadmill training using the running speed at maximal O(2) uptake and the time for which this can be maintained (Smith-2003)==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"/>.==Interval training program optimization in highly trained endurance cyclists (Laursen-2002)==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. {{:The Science of High Intensity Interval Training-table- Laursen-3-2002}}==Acute high-intensity interval training improves Tvent and peak power output in highly trained males (Laursen-2-2002)==This study used 14highly trained cyclists , [[VO2max|V̇O₂max]] of 60 (marathon equivalent of 2:43) <ref name="Laursen-2-2002"/>. They had only performed low intensity training over the previous 2 months. Half the subjects performed 4 sessions over 2 weeks of HIIT (20x 60 sec at [[VO2max|V̇O₂max]] + 120 sec recovery@ 50w) that . The HIIT group improved their peak power by 4% but had no change in [[VO2max|V̇O₂max]].=HIIT and Weight Loss===The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women (Trapp-2008)==This is a rather different study, focusing on 45 young women who are sedentary and on the upper end of the normal BMI scale (~22-24 Kg/m²), but healthy. Their [[VO2max| V̇O₂max]] was ~30, which would translate to about a 5-hour marathon. The subjects were split into three groups, interval training, continuous training, and a control group (few studies on HIIT include a control group.) The interval group did up to 60x 8 seconds 'all out' cycling, 12 seconds rest (HIIT-SIxAO). The continuous group did up to 40 minutes cycling at 60% [[VO2max|V̇O₂peak]]. The interval group started with as little as 5 minutes of intervals, building up to 20 minutes, at which point the resistance was increased. By the end of 2 weeks all interval subjects were completing the 20 minutes. Likewise, the continuous training group started with 10-20 minutes and gradually built up to the full 40 minutes. [[VO2max| V̇O₂max]] increased by ~24% for the interval training group and ~19% for the continuous group. Perhaps more interestingly, the weight of the continuous training group didn't change, but the interval training group lost weight. The interval training group lost body fat (~2.5Kg/5lb), while the continuous training group actually gained some body fat (~0.5Kg/1lb). This study used an unusually large number of unusually short intervals for the HIIT group. Sadly, I couldn't work out what intensity constituted "all out." This is a study that used a much higher number of repetitions than I see most runners performing. [[File:Trapp-2008-FM.jpg|center|thumb|300px|]]Fasting insulin also dropped far more for the interval training group than the other groups.[[File:Trapp-2008-FI.jpg|center|thumb|300px|]]'''Conclusion''': For sedentary women, HIIT improved [[VO2max| V̇O₂max]] and fasting insulin more than continuous exercise, and HIIT resulted in weight loss that did not occur in continuous exercise. ==Impact of exercise intensity on body fatness and skeletal muscle metabolism (Tremblay-1994)==The combination of Continuous Moderate Exercise and moderate intensity intervals (60-70% [[VO2max|V̇O₂max]]) reduced body fat more than Continuous Moderate Exercise alone, even though the Continuous Moderate Exercise burned over twice the calories<ref name="LaursenTremblay-1994"/>. This study doesn't have the details I would've liked, and it uses skinfold thickness to estimate body fat. The study "corrects" the reduction in body fat based on the calories burned in each training regime, something that seems dubious at best. Neither group lost any weight, but the HIIT group lost an average of 13.9 mm from the sum of six skinfold sites, compared with 4.5mm for the controls. However, the HIIT group had an average of 15 mm extra body fat at the start.==High-intensity interval exercise induces 24-h energy expenditure similar to traditional endurance exercise despite reduced time commitment (SkellyAndrews2014)==Nine men with [[VO2max|V̇O₂max]] of ~46 (3:25 marathon equivalent) were tested three times to evaluate their 24-2002hour energy expenditure<ref name="SkellyAndrews2014"/>. The trails were endurance, HIIT, and no exercise as the control. HIIT was cycling 10x (60 seconds @ ~90% Max HR with 60 second recoveries at 50w). The endurance was 70% max HR for 50 minutes. The 24-hour energy expenditure was similar for both HIIT and endurance, even though HIIT was less than half the time and required less than half the mechanical work than the endurance protocol. This suggests that the post-exercise energy increase of HIIT might be one of the mechanisms behind improved weight loss.

<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!!V̇olume!!, 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!!V̇olume!!, 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. Marshall, Effects of 4-wk training using Vmax/Tlim on VO2max and performance in athletes., Med Sci Sports Exerc, volume 31!!V̇olume!!, issue 6, pages 892-6, Jun 1999, PMID [http://www.ncbi.nlm.nih.gov/pubmed/10378918 10378918]</ref><ref name="Stepto-1999"> 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!!V̇olume!!, issue 5, pages 736-41, May 1999, PMID [http://www.ncbi.nlm.nih.gov/pubmed/10331896 10331896]</ref><ref name="Westgarth-Taylor-1997"> 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!!V̇olume!!, issue 4, pages 298-304, 1997, PMID [http://www.ncbi.nlm.nih.gov/pubmed/9134360 9134360]</ref><ref name="Lindsay-1996"> 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!!V̇olume!!, issue 11, pages 1427-34, Nov 1996, PMID [http://www.ncbi.nlm.nih.gov/pubmed/8933495 8933495]</ref><ref name="Franch-1998"> 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!!V̇olume!!, issue 8, pages 1250-6, Aug 1998, PMID [http://www.ncbi.nlm.nih.gov/pubmed/9710865 9710865]</ref><ref name="Gorostiaga-1991"> 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!!V̇olume!!, issue 2, pages 101-7, 1991, PMID [http://www.ncbi.nlm.nih.gov/pubmed/1748098 1748098]</ref><ref name="Hickson-1977"> RC. Hickson, HA. Bomze, JO. Holloszy, Linear increase in aerobic power induced by a strenuous program of endurance exercise., J Appl Physiol, volume 42!!V̇olume!!, issue 3, pages 372-6, Mar 1977, PMID [http://www.ncbi.nlm.nih.gov/pubmed/838658 838658]</ref><ref name="Helgerud-2007"> 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!!V̇olume!!, issue 4, pages 665-71, Apr 2007, doi [http://dx.doi.org/10.1249/mss.0b013e3180304570 10.1249/mss.0b013e3180304570], PMID [http://www.ncbi.nlm.nih.gov/pubmed/17414804 17414804]</ref><ref name="BurgomasterHowarth2007">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!!V̇olume!!, issue 1, 2007, pages 151–160, ISSN [http://www.worldcat.org/issn/0022-3751 0022-3751], doi [http://dx.doi.org/10.1113/jphysiol.2007.142109 10.1113/jphysiol.2007.142109]</ref><ref name="Trapp-2008"> 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!!V̇olume!!, issue 4, pages 684-91, Apr 2008, doi [http://dx.doi.org/10.1038/sj.ijo.0803781 10.1038/sj.ijo.0803781], PMID [http://www.ncbi.nlm.nih.gov/pubmed/18197184 18197184]</ref><ref name="Tremblay-1994"> A. Tremblay, JA. Simoneau, C. Bouchard, Impact of exercise intensity on body fatness and skeletal muscle metabolism., Metabolism, volume 43!!V̇olume!!, issue 7, pages 814-8, Jul 1994, PMID [http://www.ncbi.nlm.nih.gov/pubmed/8028502 8028502]</ref><ref name="Laursen-1-2002"> 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!!V̇olume!!, issue 1, pages 53-73, 2002, PMID [http://www.ncbi.nlm.nih.gov/pubmed/11772161 11772161]</ref><ref name="TjonnaLee2008">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!!V̇olume!!, issue 4, 2008, pages 346–354, ISSN [http://www.worldcat.org/issn/0009-7322 0009-7322], doi [http://dx.doi.org/10.1161/CIRCULATIONAHA.108.772822 10.1161/CIRCULATIONAHA.108.772822]</ref><ref name="Burgomaster-2005"> 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!!V̇olume!!, issue 6, pages 1985-90, Jun 2005, doi [http://dx.doi.org/10.1152/japplphysiol.01095.2004 10.1152/japplphysiol.01095.2004], PMID [http://www.ncbi.nlm.nih.gov/pubmed/15705728 15705728]</ref><ref name="Gibala-2006"> 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!!V̇olume!!, issue Pt 3, pages 901-11, Sep 2006, doi [http://dx.doi.org/10.1113/jphysiol.2006.112094 10.1113/jphysiol.2006.112094], PMID [http://www.ncbi.nlm.nih.gov/pubmed/16825308 16825308]</ref><ref name="Laursen-2-2002"> 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!!V̇olume!!, issue 4, pages 336-48, Aug 2002, PMID [http://www.ncbi.nlm.nih.gov/pubmed/12442351 12442351]</ref><ref name="Laursen-3-2002"> 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!!V̇olume!!, issue 11, pages 1801-7, Nov 2002, doi [http://dx.doi.org/10.1249/01.MSS.0000036691.95035.7D 10.1249/01.MSS.0000036691.95035.7D], PMID [http://www.ncbi.nlm.nih.gov/pubmed/12439086 12439086]</ref>

<ref name="EarnestTjønna2013">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!!V̇olume!!, issue 5, 2013, pages e65382, ISSN [http://www.worldcat.org/issn/1932-6203 1932-6203], doi [http://dx.doi.org/10.1371/journal.pone.0065382 10.1371/journal.pone.0065382]</ref><ref name="Bassett2000">David R. Bassett, Limiting factors for maximum oxygen uptake and determinants of endurance performance, Medicine & Science in Sports & Exercise, 2000, pages 70, ISSN [http://www.worldcat.org/issn/0195-9131 0195-9131], doi [http://dx.doi.org/10.1097/00005768-200001000-00012 10.1097/00005768-200001000-00012]</ref><ref name="Billat-2000">VL. Billat, J. Slawinski, V. Bocquet, A. Demarle, L. Lafitte, P. Chassaing, JP. Koralsztein, Intermittent runs at the velocity associated with maximal oxygen uptake enables subjects to remain at maximal oxygen uptake for a longer time than intense but submaximal runs., Eur J Appl Physiol, volume 81, issue 3, pages 188-96, Feb 2000, doi [http://dx.doi.org/10.1007/s004210050029 10.1007/s004210050029], PMID [http://www.ncbi.nlm.nih.gov/pubmed/10638376 10638376]</ref><ref name="ZavorskyMontgomery1998">Gerald S. Zavorsky, David L. Montgomery, David J. Pearsall, Effect of intense interval workouts on running economy using three recovery durations, European Journal of Applied Physiology, volume 77, issue 3, 1998, pages 224–230, ISSN [http://www.worldcat.org/issn/1439-6319 1439-6319], doi [http://dx.doi.org/10.1007/s004210050326 10.1007/s004210050326]</ref><ref name="Hill-1997">DW. Hill, AL. Rowell, Responses to exercise at the velocity associated with VO2max., Med Sci Sports Exerc, volume 29, issue 1, pages 113-6, Jan 1997, PMID [http://www.ncbi.nlm.nih.gov/pubmed/9000163 9000163]</ref><ref name="Lucia2000">A. Lucia, The slow component of VO2 in professional cyclists, British Journal of Sports Medicine, volume 34, issue 5, 2000, pages 367–374, ISSN [http://www.worldcat.org/issn/03063674 03063674], doi [http://dx.doi.org/10.1136/bjsm.34.5.367 10.1136/bjsm.34.5.367]</ref><ref name="Billat-1999">VL. Billat, L. Mille-Hamard, B. Petit, JP. Koralsztein, The role of cadence on the VO2 slow component in cycling and running in triathletes., Int J Sports Med, volume 20, issue 7, pages 429-37, Oct 1999, doi [http://dx.doi.org/10.1055/s-1999-8825 10.1055/s-1999-8825], PMID [http://www.ncbi.nlm.nih.gov/pubmed/10551337 10551337]</ref><ref name="Westgarth-TaylorHawley1997">Christopher Westgarth-Taylor, John A. Hawley, Scott Rickard, Kathryn H. Myburgh, Timothy D. Noakes, Steven C. Dennis, Metabolic and performance adaptations to interval training in endurance-trained cyclists, European Journal of Applied Physiology, volume 75, issue 4, 1997, pages 298–304, ISSN [http://www.worldcat.org/issn/1439-6319 1439-6319], doi [http://dx.doi.org/10.1007/s004210050164 10.1007/s004210050164]</ref> <ref name="Parra-2000">J. Parra, JA. Cadefau, G. Rodas, N. Amigó, R. Cussó, The distribution of rest periods affects performance and adaptations of energy metabolism induced by high-intensity training in human muscle., Acta Physiol Scand, volume 169, issue 2, pages 157-65, Jun 2000, doi [http://dx.doi.org/10.1046/j.1365-201x.2000.00730.x 10.1046/j.1365-201x.2000.00730.x], PMID [http://www.ncbi.nlm.nih.gov/pubmed/10848646 10848646]</ref><ref name="Tabata-1997">I. Tabata, K. Irisawa, M. Kouzaki, K. Nishimura, F. Ogita, M. Miyachi, Metabolic profile of high intensity intermittent exercises., Med Sci Sports Exerc, volume 29, issue 3, pages 390-5, Mar 1997, PMID [http://www.ncbi.nlm.nih.gov/pubmed/9139179 9139179]</ref><ref name="Balsom-1992">PD. Balsom, JY. Seger, B. Sjödin, B. Ekblom, Maximal-intensity intermittent exercise: effect of recovery duration., Int J Sports Med, volume 13, issue 7, pages 528-33, Oct 1992, doi [http://dx.doi.org/10.1055/s-2007-1021311 10.1055/s-2007-1021311], PMID [http://www.ncbi.nlm.nih.gov/pubmed/1459748 1459748]</ref><ref name="Belcastro-1975">AN. Belcastro, A. Bonen, Lactic acid removal rates during controlled and uncontrolled recovery exercise., J Appl Physiol, volume 39, issue 6, pages 932-6, Dec 1975, doi [http://dx.doi.org/10.1152/jappl.1975.39.6.932 10.1152/jappl.1975.39.6.932], PMID [http://www.ncbi.nlm.nih.gov/pubmed/765313 765313]</ref><ref name="BuchheitLaursen2013">Martin Buchheit, Paul B. Laursen, High-Intensity Interval Training, Solutions to the Programming Puzzle, Sports Medicine, volume 43, issue 5, 2013, pages 313–338, ISSN [http://www.worldcat.org/issn/0112-1642 0112-1642], doi [http://dx.doi.org/10.1007/s40279-013-0029-x 10.1007/s40279-013-0029-x]</ref><ref name="Billat-2001">LV. Billat, Interval training for performance: a scientific and empirical practice. Special recommendations for middle- and long-distance running. Part II: anaerobic interval training., Sports Med, volume 31, issue 2, pages 75-90, Feb 2001, PMID [http://www.ncbi.nlm.nih.gov/pubmed/11227980 11227980]</ref><ref name="Midgley-2006">AW. Midgley, LR. McNaughton, M. Wilkinson, Is there an optimal training intensity for enhancing the maximal oxygen uptake of distance runners?: empirical research findings, current opinions, physiological rationale and practical recommendations., Sports Med, volume 36, issue 2, pages 117-32, 2006, PMID [http://www.ncbi.nlm.nih.gov/pubmed/16464121 16464121]</ref><ref name="SkellyAndrews2014">Lauren E. Skelly, Patricia C. Andrews, Jenna B. Gillen, Brian J. Martin, Michael E. Percival, Martin J. Gibala, High-intensity interval exercise induces 24-h energy expenditure similar to traditional endurance exercise despite reduced time commitment, Applied Physiology, Nutrition, and Metabolism, volume 39, issue 7, 2014, pages 845–848, ISSN [http://www.worldcat.org/issn/1715-5312 1715-5312], doi [http://dx.doi.org/10.1139/apnm-2013-0562 10.1139/apnm-2013-0562]</ref><ref name="ZunigaBerg2011">Jorge M Zuniga, Kris Berg, John Noble, Jeanette Harder, Morgan E Chaffin, Vidya S Hanumanthu, Physiological Responses during Interval Training with Different Intensities and Duration of Exercise, Journal of Strength and Conditioning Research, volume 25, issue 5, 2011, pages 1279–1284, ISSN [http://www.worldcat.org/issn/1064-8011 1064-8011], doi [http://dx.doi.org/10.1519/JSC.0b013e3181d681b6 10.1519/JSC.0b013e3181d681b6]</ref>