The Wonder of High Intensity Interval Training

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Interval trainingInterval training was first introduced and credited to Dr. Woldemer Grsecher of Germany. It was approximately 1930 when this training technique was first unveiled (Stone, 1988; & A positive interval addition to speed, 1978). It took around 20 years for this form of training to take root in the United States, its first use being during the 1950s (Stone, 1988; & A positive interval addition to speed, 1978). This form of training was first played around with, by a Finnish athlete by the name of Pihkala in the 1900s. However, the true credit for fully adopting this training technique was the great Czech, Emil Zatopek, due to the seriousness in which he employed interval training (Stone, 1988; & A positive interval addition to speed, 1978). Over the past several decades, interval training has managed to play a significant role and create a large impact on the way in which sport is done (Stone, 1988). For a great period of time and still today, coaches have trained with the belief that long continuous work was the best and only way to train cardio. However, the vast body of research on interval training has added to the ground breaking changes in the way coaches train athletes to improve VO2 max.
The theory behind interval training rests in the physiological fact that an athlete can produce a much greater total work load in a training session if the bouts of exercise are spaced by periods of recovery (Powers, 2007; Sawka 1979; & Stone 1988). If exercise is not continuous then the extent in which heart rate and blood pressure recovery between sets depends on the level of an athlete’s fitness, environmental conditions, and the duration and intensity of the exercise (Sawka, 1979; & Powers, 2007). When training in a relatively cool environment with light effort, there is generally complete recovery between sets within several minutes (Sawka, 1979; & Powers, 2007). However, if the athlete is training at an intense level of exertion or the environment is hot and humid, there is a cumulative effect that causes an increase of the heart rate between sets (Sawka, 1979; & Powers, 2007).

Nearly all sports require endurance. Sports such as cycling, boxing, and cross country skiing place tremendous amount of strain on the aerobic system. Along with sports that can last for a great duration of time and a long season will produce a large toll on the athlete’s body; for an athlete to be able to succeed in these sorts of scenarios at highly competitive levels they must be in extremely good shape prior to the season beginning (Sandler, 2005). An effective way of testing ones fitness level is to measure their VO2 max. VO2 max is the maximum oxygen uptake. This means it is the greatest rate of oxygen uptake by the body. This is measured during severe dynamic exercise, usually done on a cycle ergometer or a treadmill. In order to improve one’s VO2 max there are many different approaches. However, it is generally believed that high intensity intervals are more effective in improving VO2 max, and the lactate threshold then low intensity intervals and continuous work training (Fox, 1975; Fox, 1974; Knuttgen, 1973; Powers, 2007, & Laursen 2002)

When using the interval training technique Klafs, 1981 (p.137) puts forward four key factors: (also refer to Allsen, 1978; & Powers, 2007 for similar models)

 

  1. A specific distance or time that is repeated a given number of times
  2. A recovery period during which the athlete jogs slowly or walks briskly and relaxes
  3. A predetermined pace or heart rate at which the athlete covers the set distance or time
  4. A predetermined number of repetitions in completing the target distance or time.

When using this model the first question one must approach is what the athlete is trying to accomplish in order to determine the optimal length and intensity of the work interval. For example, a longer work interval will require a greater involvement of aerobic energy production, while a shorter, more intense interval involves greater participation of anaerobic metabolism. Therefore, interval training that is designed to improve VO2 max will generally utilize intervals longer than sixty seconds to maximise involvement of aerobic ATP production (Powers, 2007).

The majority of textbooks and articles summarizing the findings on interval training and VO2 max are out of date. The body of knowledge on the subject has continued to grow, particularly with research on elite athletes. In order to look more thoroughly at the effect high intensity interval training has on VO2, we will summarize the methodologies and key findings of many more recent studies in order to expand and strengthen our understanding.

Helgerud, Hoydal, Wang, Karlsn, Berg, Bjerkass, et al. (2007) conducted a study, which looked at whether VO2 max increases greater by high intensity interval training versus moderate training. Fifty five healthy, non-smoking male university students were recruited for participation. All the subjects were participating in endurance training and leisure physical activity time three times per week. The subjects were randomly assigned to one of four groups. Over the course of the study 13 subjects dropped out due to health issues not related to the study. Further, two subjects were excluded for participating in less than 90% of the training regimen. This left a working sample of 40 subjects who were 24.6+/-3.8 yr, 182 +/- 6cm, and 82 +/-12 kg. Atechnogym Runrace treadmill calibrated for inclination and speed at an inclination of 5.3% , was used for all the physical capacity measurements for VO2 max, lactate threshold, work economy, all ventilator parameters, and pulmonary gas exchange were obtained using the cortex metamax II portable metabolic test system. All subjects where familiarized with the testing equipment twice before initial testing. Testing was done with an increase in intensity every minute which equated to exhaustion at 3-6 minutes. The test was stopped when VO2 max no longer rose even though intensity had. The training interventions for the four groups was as follows

  1. Long slow distance running (LSD): The first group performed a continuous run at 70% HR max (137 T 7 bpm) for 45 min.
  2. Lactate threshold running (LT): The second group performed a continuous run at lactate threshold (85% HR max , 171 T 10 bpm) for 24.25 min.
  3. 15/15 interval running (15/15): The third group performed 47 repetitions of 15-s intervals at 90–95% HR max (180 to 190 T 6 bpm) with 15 s of active resting periods at warm-up velocity, corresponding to 70% HR max (140 T 6 bpm) between.
  4. 4*4-min interval running (4*4 min): A fourthgroup trained 4*4-min interval training at 90–95% HR max (180 to 190 T 5 bpm) with 3 min of active resting periods at 70% HR max (140 T 6 bpm) between each interval.

Results of the study found that high intensity aerobic interval training resulted in significantly increased VO2 max compared with long slow distance and lactate threshold intensities (p<0.01). VO2 max in both the 15/15 and 4*4 min groups improved by 7.2% respectively. Stroke volume (SV) increased significant by approximately 10% after interval training. Therefore indicating the change in VO2 max corresponds closely with the change in SV.

Esfarjany and Laursen (2006) conducted a study, which looked at the manipulation of high intensity interval training and the effects it has on VO2 max, the lactate threshold and 3000m running performance in moderately trained males. Seventeen moderately trained male runners who had 2-3 years of run training experience volunteered to participate in the study. The subjects had not participated in any high intensity training (HIT) for 3 months prior to this investigation and the average training distance during the study was 38+/- 4 km week, which was similar to training distance prior to the study. The subject working sample was 19+/-2 years, 172+/-4cm, 73+/-3kg. Subjects were asked to rest for 48 hours prior to baseline data along with keeping a two day food log. They were intern asked to replicate their diet prior to the post training test session. Subjects were allotted 60 minutes to familiarize themselves with the equipment. The testing occurred over a three separate days. Day one tested VO2 max, day two tested time to exhaustion at VO2 max, and day three tested 3000m running time trial on indoor 200 m track. Each test was separated by greater or equal to 48 hour period and were complete within a 1-week period. The subjects were divided into three different subject groups based on their 3000m performance time. All subjects underwent a ten week training program. Groups 1 and 2 were HIT training and group 3 was a control group. Group 1 and 2 performed two HIT sessions and two 60 min recovery sessions (75% VO2 max) a week. Group 3 performed four 60 min recovery runs (75% VO2 max) a week. In Group 1 significant improvements were found (P<0.05) in VO2 max (+9.1%), Tmax (+5%), Vlt (11.7%), and 3000 m TT (-7.3%). In Group 2 significant improvement was also observed (P<0.05) in VO2 max (+6.2%), Tmax (+32%), and 3000 m TT (-3.4%), but not in Vlt (+4.7%; P=0.07). No significant changes occurred in the control group.

Billat, Flechet, Petit, Muriaux, and Kiralsztein (1999) conducted a study, which looked at interval training effects on aerobic performance and overtraining markers at VO2 max. Eight endurance trained male athletes volunteered to participate in this study. The athletes specialised in 1500m to half marathon distance running. The working sample was 24+/-3.2 years, 175.0+/-3.3cm, and 65+/-4.5kg. The study took place over 11 weeks and was broken down as follows: week 1 before normal training 1 incremental test to determine Vo2max and OBLA, 1 all run at VO2 max to determine time to exhaustion at vVO2max. Week 2-5 normal training took place which comprised of 1 vVO2 max interval training and 1 OBLA per week. Week 6 was test week. Week 7-10 were overload training: 3 vVO2 max interval training and 1 OBLA per week. Week 11 was test week. All tests during test week were separated by equal to or greater than 48 hours and all tests were completed within 1 week. Tests were performed on a treadmill with 0% slope. Data was collected using EOS-Spring automated metabolic cart, and a MAX-1 electro cardiograph. The 4th week normal training regimen significantly improved the velocity associated with VO2 max (20.5+/-0.7 vs 21.1+/-0.8 km*h, P=0.02), VO2 max was not significantly different (71.6+/- 4.8 vs 72.7+/-4.8ml*min*kg), time to exhaustion at vVO2 max was not significantly different (301+/-56 vs 283 +/-41s), performance distance was not significantly different (2052.2+/-331 vs 1986.2+/-252.9m. After overload week performance was not significantly affected even though a significant increase in plasma noradrenaline occurred.

McKay, Patterson, and Kowalchuck (2009) conducted a study, which looked at the effect of short term high intensity interval training vs. continuous training on O2 uptake kinetics, muscle deoxygenating, and exercise performance. Twelve young adult males 25+/-4 years, 83+/-7kg, VO2= 3.68+/-0.47l/min. Subjects were randomly assigned to either a high intensity (low volume) interval training continuous endurance training. Subjects were all recreationally active and were told to refrain from beginning any other training until the completion of the study. The subjects had three opportunities on separate occasions to 1 week prior to baseline testing to familiarize themselves with the equipment used to evaluate training status. Subjects performed 3 separate tests 1) ramp incremental (RI) test, 2) a constant load, moderate intensity exercise test at a work rate (WR) at approximately 90% of their lactate threshold, and 3) a time, constant load performance test to volitional fatigue at a WR corresponding to the high WR achieved during the RI test; all testing was completed on a cycle ergometer. Subjects were tested on three separate days with at least 24 hours of rest between test, testing was done approximately the same time of day. Gas exchange measurement was completed using a bi-directional turbine. Local muscle oxygenation was monitored by near-infared spectroscopy. Training was initiated 2-3 days post baseline test and consisted of either eight sessions of HIT or 8 sessions of END performed over a 19 day period. Each training period was separated by 1-2 days of rest. Training was conducted on friction braked cycle ergometer and was monitored by one investigator. The results to the RI test, VO2p kinetics, Hr Kinetics, and exercise performance found no significant difference between HIT and END training groups over the course of the study.

O’Brien, Wibskov, Knez, Paton, and Harvey (2008) conducted a study, which looked at the effect exercise duration and intensity in interval training can play on oxygen consumption during treadmill running. Fourteen moderately trained males and three females volunteered to participate in this study. The working sample was 21.9+/-3.9 years, 74+/-11.3kg, VO2 peak= 57.4+/-8.7 ml*kg*min. To establish weather interval training (INT) compared to constant rate training (CRT) differentially affects VO2 during treadmill running each subject completed three treatments twice in a balanced random with equal to or greater than 72 hours separating treatment exposure. The treatments were standardized over 20 min for average speed running and were structured as follows: treatment 1, 1 min INT 10* 1 min efforts at the velocity corresponding to VO2 peak interspersed with 10*1 min efforts at 0.5 VO2 peak; treatment 2, 2 min INT 5*2 min efforts at Vpeak interspersed with 5*2 min efforts at 0.5 Vpeak; Treatment 3, CRT 20 min constant rate run on a treadmill at a velocity equivalent too, and determined by the mean velocity of treatment a and b (75% Vpeak. The subjects began the study by performing a maximal treadmill test to establish VO2 peak and its corresponding velocity (Vpeak). The subjects began running at 9 kmh each minute the speed was increased by 1kmh until exhaustion. Subjects where fitted with a two way breathing valve and the expired air was collected by an online metabolic cart system. Post baseline test the subjects were randomly assigned to one of the treatment conditions before commencing the experimental protocol. Subjects were asked to follow some nutrition and sleep guidelines. Each participant complete a 5 min treadmill warm up with 3 min rest period. They were then attached to the metabolic analysis cart, the expired air was then collected. The subjects then began to run according to their experimental treatment while being continuously recorded in 30 s segments during the 20 min run. Both INT groups had significantly higher mean VO2 the CRT. The 2 min INT group resulted in having significantly greater number of times VO2 peak exceeded 90% during treatment than the 1 min INT. Therefore, the conclusion the authors came to was INT is a more powerful way of stimulating VO2 peak for improvement and subsequent endurance performance than CRT.

Breil, Weber, Koller, Hoppeler, and Vogt (2010) conducted a study, which looked at Block training periodization in apling skiing and the effect an 11 day HIT training program can have on VO2max and performance. Twenty two elite junior alpine skiers from a national train center were recruited to take part in this study. One male dropped out due to medical condition unrelated to the study. The working sample was 15 males and 6 females who have trained for greater than 3 years, age= 17.4+/-1.1 years, height= 172.6+/- 10.5cm, body mass 66+/-11. The study took place during off seasons in preparation for the coming season. The tests took place under controlled conditions at the national training center 1,050 m above sea level. After the subjects had become familiar with the performance testing equipment they were divided into HIT (n=13) and control training (CT, n=8) groups were matched based on VO2 max. The subjects then carried on with regular training for 3 weeks before the baseline testing. After the baseline test the 11 day training intervention took place. 7 days after the intervention the post intervention test was completed with the subjects being asked to avoid strenuous exercise for 24 hours before all testing. The HIT group performed HIT for a total of 15 sessions over 3 day training block. Each training block was separated by a day of rest. The Hit sessions consisted of four 4- min bouts at 90-95% of the subject’s maximal heart rate separated by 3 min of active recovery. The testing was performed either on a cycle ergometer or a ski-specific obstacle course. The intensity was being monitored by continuous heart rate monitoring, and periodical perceived exertion rating and blood lactate measurements. The CT group maintained their normal endurance and strength training during the intervention period. The HIT group significantly improved in VO2 by 6% (p<0.01), relative peak power output by 5.5% (p<0.01), and power output at ventilator threshold 2 by 9.6% (p<0.01) No Changes occurred for these measurements in CT. Tlim remained unchanged for both groups. Males in HIT group only saw improvement in high box jump performance. Hit training offers a promising method for alpine skiers to efficiently improve V02 max and performance.

Winsloff, Stoylen, Loennechen, Bruvold, Rogenmo, Haram, et al (2007) conducted a study, which looked at interval training versus moderate continuous training in heart failure patients to determine which produces a superior cardiovascular effect. Twenty seven patients (age 75+/-11.1 years, left ventricular ejection fraction 29%, VO2 peak 13ml*kg*min) with stable postinfarction heart failure were enrolled from the department of cardiology. The patients were all undergoing proper medical treatment with medications such as ϐ-blockers and angiotensin-converting enzyme inhibitors. The subjects were randomized into either moderate continuous training or aerobic interval training for 3 times per week, for 12 weeks or to a control group that received standard advice regarding physical activity. Moderate continuous training is performed at 70% of the highest measured heart rate. Interval training is to be performed at 95% of peak heart rate. VO2 increased significantly more in interval training than continuous training (46% vs 14%, P<0.001) and was associated with reverse LV remodelling. LV end-diastolic and end-systolic volumes declined with aerobic training by 18% and 25%; LV ejection fraction improved by 35%. Also, pro-brain natriuretic peptide decreased 40%. Improvement in brachial artery flow-mediated dilation was also improved greater by aerobic interval training. Further, mitochondrial function in the lateral vastus muscle only improved in aerobic interval training. The intensity of the exercise proved to play a major role in reversing LV remodelling and improving aerobic capacity.

Current research and Data only goes further in supporting the historical findings on the effectiveness of interval training. High intensity Interval training is clearly the most effective manner in which to train VO2 max to date. However, in acute training there is debate on whether there is a significant difference between interval training and continuous training in untrained individuals; but it has been found fairly conclusively that acute high intensity interval training makes significant difference in elite athletes. Further, Interval training appears to be an effective and efficient way of training for a multitude of sports; since it improves VO2max the fastest and produces other changes such as increased vertical jump and lactic acid tolerance, improved mitochondrial function, etc. Finally, interval training has proven to be very effective in improving VO2 max and heart recovery of heart failure patients. The research on HIT and VO2 improvement is highly lacking in terms of research on women, nearly all studies are comprised of all male or mostly all male population groups; further research on the effect interval training has on women is necessary.
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