"If we knew what we were doing, it would not be called research, would it?"
- Albert Einstein
Overview of the Research
We have reviewed and summarized many peer-reviewed research articles on HIIT in order to create our workouts and programs. The research shows that HIIT can be more effective and efficient than traditional steady-state moderate-intensity endurance training (ET) for most people. You will also find the seven major benefits of HIIT as supported by science. The articles are listed based on the number of times each article was cited by other studies. Thus, some of the most recent research will have less citations than older publications.
You can read the summaries below or download a PDF version of the research for free to read later. There is a table of contents so that you will be able to jump to any studies that are more interesting for you. If there are any articles that you don’t see here and would like for us to summarize, please send them our way. This information is current as of August 1, 2017.
The Seven Major Benefits of HIIT
HIIT takes less time than traditional steady-state cardio to improve the following health conditions:
Aerobic and Anaerobic Fitness
HIIT has the greatest effect on your Aerobic and Anaerobic Fitness. Aerobic Fitness is your body's ability to use oxygen to produce energy for moderate-intensity long-duration exercises (i.e. walking or long distance running). Anaerobic Fitness is your body's ability to produce energy without oxygen for high-intensity short-duration exercises (i.e. sprinting or weightlifting). HIIT has been shown in multiple studies to improve both Aerobic and Anaerobic Fitness to a similar or even greater degree than traditional endurance training (ET) despite much less time and less work volume. The significant increase in your maximal oxygen uptake (VO2max) is the primary benefit of HIIT.
Cardiovascular Health refers to the condition of your heart and your body's blood vessels. HIIT has been studied on patients with metabolic syndrome (i.e. conditions such as high blood pressure, high blood sugar, excess body fat, that are associated with cardiovascular disease) and coronary artery disease with significantly positive results. HIIT can help prevent heart disease.
Blood Pressure (BP) is the force of your blood moving through blood vessels at moments of rest. HIIT has been shown to be as effective as ET at decreasing Systolic BP (pressure during contraction of the heart) and decreasing Diastolic BP (pressure during rest).
Insulin is a hormone that regulates blood sugar levels. Insulin Sensitivity is the relationship between the amount of insulin that needs to be produced in order to deposit glucose into the blood stream. A person who is insulin-sensitive only needs to produce a small amount of insulin in order to balance their blood glucose levels. A person who is insulin-resistant needs to produce or inject insulin in order to balance their blood glucose levels. HIIT has been tested on patients with metabolic syndrome and Type-2 Diabetes with significantly positive results.
Several studies below compare the difference betweens HIIT and ET on fat oxidation. HIIT can be as helpful as ET in decreasing body weight because it can burn more calories during and after exercise. HIIT resulted in a nine times greater reduction in subcutaneous fat than the ET group even though the HIIT group had a much lower volume of exercise and time commitment. Additionally, two weeks of HIIT three times per week in moderately active women increased fat oxidation to a level comparable to ET.
HIIT has many benefits for muscular health by improving muscle oxidative capacity, muscular glucose uptake, muscular endurance and muscle mass. Muscle oxidative capacity is the ability of muscle to use oxygen during extended periods of resistance. Many studies show that low-volume HIIT increases skeletal muscle oxidative capacity to a similar level of ET. HIIT has also been shown to increase GLUT4 activity which is responsible for the uptake of glucose in the muscles and is important for recovery. HIIT can also increase muscular endurance and maintain or in some instances increase muscle mass. If your primary goal is to increase muscle mass, you should focus on resistance training rather than HIIT.
HIIT has been shown to increase high-density lipoprotein cholesterol (HDL-C), or the good cholesterol, after 8 weeks of training in several studies. Researchers in the same study article stated that a combination of fat loss and HIIT for 8-12 weeks would be needed to decrease low-density lipoprotein cholesterol (LDL-C) and total cholesterol levels.
Superior Cardiovascular Effect of Aerobic Interval Training Versus Moderate Continuous Training in Heart Failure Patients. Wisloff et. al., 2007. (Cited by 1354)
This study examined incline treadmill walking through HIIT (at 95% peak heart rate) versus ET (at 70% peak heart rate) for heart failure patients. The HIIT group warmed up for 10 minutes and then did HIIT (4 sets x 4 minute intervals at 90-95% peak heart rate with 3 minutes of active rest per set) followed by a 3-minute cool-down at the end. The moderate intensity group walked for 47 minutes at 70-75% of peak heart rate. The study found that VO2peak increased more with patients in the HIIT group (46% increase) than the ET group (only 14% increase).
Aerobic high-intensity intervals improve VO2max more than moderate training. Helgerud et. al., 2007. (Cited by 860).
This study compared the effects of four different types of exercise programs in healthy moderately-trained males three days a week for 8 weeks. Group 1 was long-slow distance (70% HRmax); Group 2 trained at lactate threshold (85% HRmax); Group 3 used 15/15 interval running (15 seconds of running at 90-95% HRmax followed by 15 seconds of active rest at 70% HRmax); Group 4 used 4x4 interval running (4 minutes of running at 90-95% of HRmax followed by 3 minutes of active resting at 70% HRmax). The study found that VO2max increased significantly in the 15/15 and 4x4 groups by 5.5% and 7.2%, respectively. The researchers concluded that HIIT is more effective than long slow distance running or lactate-threshold running.
Similar metabolic adaptations during exercise after low volume sprint intervals and traditional endurance training in humans. Burgomaster et. al., 2008. (Cited by 856)
This study compared the effects of Sprint Interval Training (SIT) and traditional endurance training (ET) on active individuals. SIT consisted of a Wingate Test (4-6 sets of 30 seconds of all-out intensity cycling with 4.5 min recovery between each set, 3 days/week for 6 weeks). ET consisted of 40–60 minutes of continuous cycling at a moderate intensity, 5 days/week for 6 weeks. The major finding from the study was that SIT caused muscular and metabolic adaptations that were comparable to those by ET despite a much lower training volume and time commitment.
Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscles and exercise performance. Gibala et. al., 2006. (Cited by 850)
This study focused on changes of exercise capacity after low volume SIT vs. high volume ET in two weeks. Each session consisted of either: (1) Wingate SIT (four to six repeats of 30 seconds all-out sprint cycling with 4 minutes of active recovery); (2) ET (90-120 minutes of continuous cycling at moderate intensity). The researchers concluded that SIT is a time-efficient method to cause rapid adaptions in skeletal muscle and performance comparable to ET in young active men.
Aerobic Interval Training vs. continuous moderate exercise as a treatment for the metabolic syndrome. Tjonna et. al., 2007. (Cited by 847)
This study compared the effects of ET to HIIT in participants who had metabolic syndrome (conditions such as high blood pressure, high blood sugar, excess body fat, that are associated with cardiovascular disease). Both groups did incline walking or running on a treadmill 3 times per week for 16 weeks. The HIIT group did 4 intervals of 4 minutes at 90% intensity with 3 minutes of active recovery in between each interval for a total workout time of 40 minutes. The ET group worked at 70% intensity for 47 minutes of continuous exercise. The study found that the HIIT group was superior at increasing VO2max, increasing insulin signaling in fat and skeletal muscle, skeletal muscle biogenesis and reducing blood glucose. Thus, intensity is more important than duration for reversing the risk factors of the metabolic syndrome.
Exercise and Cardiovascular Events – Placing the Risks into Perspective: A Scientific Statement from the American Heart Association Council on Nutrition, Physical Activity, and Metabolism and the Council on Clinical Cardiology. Thompson et. al., 2007 (Cited by 699)
This article discussed the potential risks of sudden cardiac death and acute myocardial infarction from vigorous activity in patients with cardiac disease. Hereditary issues are responsible for cardiac events in younger individuals while atherosclerosis is responsible for cardiac events in adults. The article states that physicians should not overestimate the risks of exercise because the benefits are likely greater. However, the likelihood of having a cardiac event is greatest in the least physically active individuals, so the article recommends that these patients should be screened and be excluded from certain activities until they begin regular physical activity. For at-risk individuals, the article recommends moderate intensity exercise through walking.
Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans. Burgomaster et. al., 2005. (Cited by 667)
This study examined whether six sessions of SIT (M/W/F for two weeks) would increase endurance capacity. Each training session consisted of 4-7 all-out Wingate SIT cycling with 7.5% of body weight resistance for 30 seconds with 4 minutes of recovery between each set. The study found that SIT increased muscle oxidative potential and doubled aerobic endurance capacity in recreationally active individuals. Remarkably, the participants in the study retook an endurance test after the SIT program by cycling at 80% V02peak and the amount of time until their exhaustion doubled from 25 minutes to 51 minutes.
The evolution of physical activity recommendations: how much is enough? Blair et. al., 2004. (Cited by 631)
Both the Centers for Disease Control and Prevention and the American College of Sports Medicine recommend that “every US adult should accumulate 30 minutes or more of moderate-intensity physical activity on most, preferably all, days of the week.” These researchers recommend that individuals commit to 30min of moderate intensity activity daily and also trying to build up to 60 minute of activity per day which will provide additional health benefits. They also state that people engage in resistance training and flexibility exercises at least twice a week.
Physiological adaptations to low-volume, high-intensity interval training in health and disease. Gibala et. al., 2012. (Cited by 625)
This study summarized findings of prior HIIT studies stating that HIIT can serve as an effective alternative to ET Since lack of time is the most commonly cited barrier to regular exercise. Additionally, HIIT causes similar and sometimes more physiological adaptations in healthy and unhealthy individuals when compared on a matched-worked basis. Finally, the researches stated that HIIT causes these adaptations despite a substantially lower time commitment and lower volume of exercise.
This study examined older participants using the treadmill in three different settings (group-based high-intensity exercise training, home-based exercise training, and home-based lower-intensity exercise training) for two years. The study found that participants who were part of the home-based high-intensity exercise training group were more likely to follow their exercise program throughout the two years of the study.
Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Tabata et. al., 1996. (Cited by 573)
This study is the basis for the popularly termed Tabata Training Protocol (20 seconds of all-out sprinting followed by 10 seconds of active recovery for a total of four minutes). Tabata’s team compared the effects of moderate-intensity endurance training (60 min/day, 5 days/week, 6 weeks at 70rpm and intensity of 70% VO2max) to HIIT (20/10 intervals at intensity of 170% VO2max, 4 days/week for 6 weeks and one day of endurance training for 30 minutes per week). The high-intensity group improved both aerobic (VO2max) and anaerobic capacity, while the moderate-intensity group only improved aerobic capacity at a percentage slightly less than the HIIT group.
Impact of exercise intensity on body fatness and skeletal muscle metabolism. Tremblay et. al., 1994. (Cited by 570)
This study examined the impact of 20 weeks of ET on one group and 15 weeks of high intensity on a second group using a cycling ergometer. The ET group exercised for 30-45 minutes per day, 4-5 times per week, at a moderate intensity. The high-intensity group performed 30 minutes of steady state exercise at an intensity of 70% of maximal heart rate reserve and interval training training of various durations from 15 seconds to 60 seconds with recovery periods. The study found that the high-intensity group had a nine times greater reduction in subcutaneous fat than the ET group even though they had a much lower volume of exercise.
Metabolic adaptations to short-term high-intensity interval training: a little pain for a lot of gain? Gibala et. al., 2008. (Cited by 551)
This article summarized the recent findings regarding how HIIT performed for 6 weeks would increase peak oxygen update (VO2peak) and the maximal activity of mitochondrial enzymes in skeletal muscle. HIIT can induce rapid changes in exercise capacity and skeletal muscle energy metabolism similar to traditional ET. The article concluded that HIIT is a time-efficient method to rapidly improve exercise capacity and fat oxidation to a level comparable to ET.
Two weeks of High-Intensity Aerobic Interval Training increases the capacity for fat oxidation during exercise in women. Talanian et. al., 2007. (Cited by 493)
This study examined HIIT’s physiological effects (through skeletal muscle fuel content, mitochondrial enzyme activities, fatty acid transport proteins, peak O2 consumption, and whole body metabolic, hormonal, and cardiovascular responses). The participants in this study performed HIIT every other day for two weeks (ten sets of 4-minute cycling bursts at intensity of 90% VO2max separated by 2 minutes of rest). Seven sessions of HIIT over a 2-week period improved whole body fat oxidation and the capacity for skeletal muscle to oxidize fat in moderately active women. The study found that HIIT is a practical exercise that can be performed by elite athletes as well as untrained individuals.
The effects of high-intensity intermittent training on fat loss and fasting insulin levels in young women. Trapp et. al., 2008. (Cited by 451)
This study examined the effects of a 15-week HIIT program on subcutaneous fat and insulin resistance in young women. The participants were randomly assigned to either HIIT (60 sets of 8 seconds of sprinting and 12 seconds of rest for 20 minutes a week three times per week), ET (40 minutes of steady-state exercise a week), or control groups (no changes to their current lifestyle). The study found that both the HIIT and ET groups showed a significant improvement in VO2peak, but only the HIIT group had a significant reduction in total body mass and abdominal fat. Additionally, the HIIT group had a 31% decrease in fasting insulin compared to 9% for ET.
A practical model of low-volume high-intensity interval training induces mitochondrial biogenesis in human skeletal muscle: potential mechanisms. Little et. al., 2010. (Cited by 427)
This study examined whether a low-volume HIIT protocol that is not an ‘all-out’ sprint session will have performance, metabolic and molecular adaptations similar to traditional ET. The study used a Modified Wingate Protocol (8-12 sets of 60 second intervals at approximately 100% peak power with 75 seconds of recovery, 3 times per week for 2 weeks). The study found that a practical HIIT program caused GLUT4 (responsible for muscle glucose uptake) to increase by 119% and resting muscle glycogen to increase by 17%. The researchers concluded that low volume HIIT increases skeletal muscle mitochondrial capacity and exercise performance at a comparable rate to ET and may represent a practical alternative to ET.
High-intensity intermittent exercise and fat loss. Boutcher et. al., 2010. (Cited by 417)
This article summarized the results of HIIT on fat loss, fitness, insulin resistance, skeletal muscle and abdominal fat loss. This article pointed to other research which showed there was a release of growth hormones after 30 seconds of maximal exercise through the Wingate test and the hormones remained above baseline post-exercise for one hour. The study also pointed to other research articles which studied Wingate tests lasting from 2 to 15 weeks which increased VO2max from between 4% and 46%. The article concludes that HIIT can result in modest reductions of abdominal body fat in young normal weight and slightly overweight males and females and greater reductions in overweight male and female type 2 diabetic individuals.
Low-volume high-intensity interval training reduces hyperglycemia and increases muscle mitochondrial capacity in patients with type 2 diabetes. Little et. al., 2011. (Cited by 390)
This study examined how HIIT impacts glucose regulation and skeletal muscle metabolic capacity in patients with Type 2 Diabetes. The patients performed six sessions of HIIT (10 x 60 seconds peak cycling / 60 seconds of recovery, three times per week for two weeks). The total weekly time commitment for HIIT was 50% lower than the American College of Sports Medicine guidelines which state 150 minutes of moderate to vigorous exercise is needed per week. The study found that low-volume HIIT can rapidly improve glucose control and induce adaptations in skeletal muscle that are linked to improved metabolic health in patients with Type 2 Diabetes.
Extremely short duration high intensity interval training substantially improves insulin action in young healthy males. Babraj et. al., 2009. (Cited by 346)
This study examined whether HIIT has the capacity to improve insulin action and glycemic control in young men. The participants completed the Wingate protocol (4-6 sets x 30 seconds all-out cycling sprints, 4 minutes of rest, 3 sessions/week for 2 weeks, 7.5% of body weight resistance). The study found that HIIT can prevent age-related development of cardiovascular disease.
Effect of short-term sprint interval training on human skeletal muscle carbohydrate metabolism during exercise and time-trial performance. Burgomaster et. al., 2006. (Cited by 321)
This study examined the effect of SIT on skeletal muscle glycogenosis and lactate accumulation for active individuals. The study used the Wingate Protocol (4-6 sets, 30 second sprints, 4 minutes’ recovery, 3 sessions per week for two weeks). The study found that sprint training improved a time trial performance by 10% despite no change in VO2peak. The study also concluded that SIT decreased net muscle glycogenosis (abnormal storage of glycogen in muscle) and lactate accumulation (which causes muscle fatigue) during matched-work exercise.
Brief intense interval exercise activates AMPK and p38 MAPK signaling and increases the expression of PGC-1alpha in human skeletal muscle. Gibala et. al., 2009. (Cited by 308)
This study examined whether HIIT would impact mitochondrial biogenesis (creation of new power generators) in human skeletal muscle. The participants performed one running Wingate protocol (4 sets of 30 seconds all out running sprints with 4 minutes of recovery between each set). The main finding was that four sets of all out 30 second sprints stimulated signaling through AMPK and p38 MAPK, which are linked to PGC-1a and the regulation of mitochondrial biogenesis and glucose and fatty acid oxidation in skeletal muscle.
Effect of 2 weeks of sprint interval training on health-related outcomes in sedentary overweight/obese men. Whyte et. al., 2010. (Cited by 300).
This study examined the effects of SIT on physiological factors in overweight/obese sedentary men. The method used was the Wingate test (4-6 repeats of 30-seconds all-out sprints on a cycle ergometer, with 4.5 minutes of recovery between each repetition, three times a week for two weeks). The study found that after 2 weeks of the Wingate test VO2max increased, waist circumferences decreased and resting fat oxidation remained elevated 24 hours post-workout.
High-intensity interval running is perceived to be more enjoyable than moderate-intensity continuous exercise: Implications for exercise adherence. Bartlett et. al., 2011. (Cited by 269)
This study examined whether running-based HIIT would be more enjoyable than moderate intensity continuous running. The study had 8 men who performed HIIT (6 sets x 3min at an intensity of 90% VO2max with 3 minutes of active recovery at an intensity of 50% VO2max) or ET (50 minutes of moderate intensity continuous running at 70% VO2max). The study found that running-based HIIT group had greater enjoyment than the ET group in active men.
Exercise and improved insulin sensitivity in older women: evidence of the enduring benefits of higher intensity training. DiPetro et. al., 2006. (Cited by 259)
This study examined the benefits of higher intensity treadmill running vs. moderate to lower intensity treadmill walking on improving insulin sensitivity in women older than 60 while holding exercise volume constant. The subjects were divided into three groups (high intensity for 55 minutes, moderate intensity for 65 minutes, and lower intensity for 45 minutes) and the study lasted for nine months. The study concluded that long-term higher intensity exercise training provides more enduring benefits to insulin action as compared with moderate or low-intensity exercise.
Sprint interval and traditional endurance training induce similar improvements in peripheral arterial stiffness and flow-mediated dilation in healthy humans. Rakobowchuk et. al., 2008. (Cited by 253)
This study examined whether SIT would have similar results to peripheral arterial stiffness to traditional endurance training using the Wingate protocol. The study found that SIT is a time-efficient strategy to elicit improvement in peripheral vascular structure and function that are comparable to endurance training. The Wingate group exercised three days per week on Mondays, Wednesday and Fridays for 6 weeks. The ET group performed 5 days per week at 65% of VO2 peak for 6 weeks for 40-60 minutes. The SIT group performed less than 10% of the volume of work for 100% of the benefit.
Effectiveness of High-Intensity Interval Training for the Rehabilitation of Patients With Coronary Artery Disease. Warburton et. al., 2005. (Cited by 253)
This study examined compared benefits of HIIT to ET for patients with coronary artery disease. The ET group had a 10-minute warm-up with 30-minutes of continuous aerobic exercise at 65% of maximum heart rate, resistance training and a 10-minute cool-down. The HIIT group had the same warm-up, resistance training and cool-down but used intervals with 2 minutes of high intensity (90% of maximum heart rate) followed by 2 minutes of recovery. The participants used a treadmill, stair climber, and an arm/leg cycling ergometer for the sessions. This study found that HIIT could be used with minimal risk to patients with coronary artery disease and had similar aerobic benefits and also had anaerobic benefits.
Aerobic interval training reduces cardiovascular risk factors more than a multitreatment approach in overweight adolescents. Tjonna et. al., 2009. (Cited by 253)
This study compared the effects of aerobic HIIT (4 x 4 min at 90% maximal heart rate with 3 minutes of active recovery twice a week for 3 months) and a multidisplinary approach (exercise, dietary and psychological advice, twice a month for 12 months) to an overweight population. The study found that HIIT was more favorable than the multidisplinary approach at increasing VO2max, reducing BMI and decreasing percentage of fat at both the 3-month period and 12-month period post-study. The participants in the HIIT group were more likely to maintain or improve their health risk factors.
High-intensity training versus traditional exercise interventions for promoting health. Nybo, 2010. (Cited by 249)
The purpose the study was to determine the effectiveness of HIIT running as exercise intervention for promoting health and to compare benefits to endurance and strength training. The study split participants into four groups: HIIT, ET, strength training and a control group. The improvement in cardiorespiratory fitness was superior in the HIIT group. 5-minute warm-up jog with 2 minutes of high intensity. Although the total training time in the HIIT group was less than one-third of the time completed by the two other training groups, HIIT induced an increase in maximal oxygen update which was far superior to the ET or strength training group.
High-intensity aerobic interval training increases fat and carbohydrate metabolic capacities in human skeletal muscle. Perry et. al., 2008. (Cited by 247)
This study investigated skeletal muscle and whole-body metabolic adaptations that occurred following HIIT for untrained individuals. The method was HIIT three days per week for six weeks (10 x 4 minute intervals at 90% peak oxygen consumption and 2 minutes of rest between each interval). This study demonstrated that HIIT is a powerful method to increase whole-body and skeletal muscle capacities to oxidize (or burn) fats and carbohydrates in previously untrained individuals.
Low-volume interval training improves muscle oxidative capacity in sedentary adults. Hood et. al., 2011. (Cited by 228)
The study examined whether a more practical low-volume submaximal constant-load HIIT protocol would impact skeletal muscle oxidative capacity and insulin sensitivity in sedentary middle-aged adults, who may be at a higher risk for inactivity-related disorders. Modified Wingate protocol (3-minute warm-up, 1-minute of 60% of peak power and 1 minute of recovery between intervals, 5- minute cool-down). GLUT4 increased by 260% and PGC-1a protein increased by 56% post exercise. Interventions that increase PGC-1a would seem to have beneficial effects on insulin sensitivity and metabolic health. The study concluded that low volume HIIT rapidly induces skeletal muscle mitochondrial biogenesis, increases GLUT4 content, and improves insulin sensitivity in previously sedentary adults.
The Potential for High-Intensity Interval Training to Reduce Cardiometabolic Disease Risk. Kessler et. al., 2012. (Cited by 227)
This article summarized various finding about HIIT's ability to understand what cardiometabolic disease means. The article stated that many articles which compared the effect of HIIT to ET found that HIIT was as good at improving of aerboic fitness and insulin sensitive. The article also stated that low-density lipoprotein cholesterol was decreased only after eight weeks of HIIT. The study concluded that HIIT seems to show as good or greater aerobic fitness and metabolic or cardiometabolic conditions.
Divergent response of metabolite transport proteins in human skeletal muscle after sprint interval training and detraining. Burgomaster et. al., 2007. (Cited by 215)
Short-term SIT induces rapid increases in skeletal muscle oxidative capacity but has divergent effects on proteins associated with glucose, lactate, and fatty acid transport. SIT induces increase in GLUT4 (responsible for glucose uptake in muscles). SIT causes rapid changes in skeletal muscles likely due to its high level of muscle fiber recruitment and the potential to stress Type II fibers specifically. SIT rapidly increased muscle oxidative potential and the proteins associated with glucose and lactate/H+ transport. This study found that the HIIT benefits lasted for six weeks of detraining (stopped SIT exercises).
The effect of in-season, high intensity interval training in soccer players. Warburton et. al., 2005. (Cited by 199)
This study examined the effect of HIIT on professional male soccer player’s running performances. The HIIT group include 2 different high-intensity sessions in addition to their training program. One day focused on 12-15 intervals of 15 seconds of high-intensity work with 15 seconds of rest. The second day focused on 12-15 all-out sprint intervals of 40-meter runs with 30 seconds of rest. The study showed that HIIT improved maximal aerobic speed and that the players’ 40-meter sprint time was decreased during the season.
Physical responses to different modes of interval exercise in patients with chronic heart failure—application to exercise training. Meyer et al., 1996. (Cited by 184)
This study is the basis for the Meyer protocol. The researchers examined the effects of three high intensity interval protocols on chronic heart failure patients. The three intervals were 30/60 seconds, 15/60 seconds and 10/60 seconds. The study then showed that the patients had a higher work rate than 75% VO2peak, but lower cardiac stress during interval exercise. The study found that all three HIIT intervals can be recommended to patients with chronic heart failure in place of steady-state continuous exercise at 75% VO2peak.
This study examined the potential mechanisms which cause low-volume HIIT to increase skeletal muscle mitochondrial capacity. Eight healthy men performed the Wingate protocol three times per week for two weeks (4 sets × 30 seconds bursts of all-out cycling with 4 min of rest). These findings support the hypothesis that low-volume HIIT activates mitochondrial biogenesis through a mechanism involving increased nuclear abundance of PGC-1α. PGC-1a is hypothesized to be a critical mediator of the muscle adaptive response to training is regarded as a key molecular target for treatment of mitochondria-related metabolic diseases. The study concluded that HIIT is an effective strategy for improving metabolic health for all.
Effects of High-Intensity Interval Walking Training on Physical Fitness and Blood Pressure in Middle-Aged and Older-People. Nemoto et. al, 2007 (Cited by 183).
This study examined whether HIIT walking was better than ET walking at increasing muscle strength, improving aerobic capacity, and reducing blood pressure. The ET group performed 8000 steps per day at 50% of their VO2peak four or more times per week. The HIIT group performed 5 sets of 3 minutes of high intensity followed by 3 minutes of low-intensity four or more times per week. The study found that HIIT group had increased knee extension and flexion capability, increased aerobic capacity for walking by 9% and reduced systolic blood pressure more than the ET group.
Manipulating high-intensity interval training: effects on VO2max, the lactate threshold and 3000m running performance in moderately trained males. Esfarjani et. al, 2007. (Cited by 176)
This study examined the impact of two HIIT programs on VO2max, the lactate threshold and 3000m running performance in moderately training male runners. Group 1 performed 8 sets of 60% of maximum amount of time for VO2 max in 1 to 1 work to recovery ratio two times per week along with two steady-state sessions per week for 10 weeks. Group 2 performed 12 sets of 30 seconds at 130% VO2max with 4.5 minutes of recovery between each set two times per week along with two steady-state sessions for 10 weeks). The control group performed four 60-minute steady-state sessions (75% VO2max) per week for ten weeks. The study concluded that VO2max, lactate threshold and 3000m running performance can be significantly improved through HIIT programs in moderately trained runners, but that Group 1’s HIIT program was more favorable.
Impact of high-intensity exercise on energy expenditure, lipid oxidation and body fatness. Yoshioka et. al., 2001. (Cited by 171)
This study examined why men who regularly take part in intense physical activities display lower fat percentage and subcutaneous adiposity (fat around waste) than men who never perform such activities, and this was true even if the latter group reported a lower energy intake. The high-intensity exercise stimulus produced a greater post-exercise oxygen consumption as well as fat oxidation than the resting session. The study found that high-intensity exercise favors a lesser body fat deposition which might be related to an increase in post-exercise energy metabolism.
Effects of high-intensity intermittent swimming on PGC-1a protein expression in rat skeletal muscle. Terada et. al., 2005. (Cited by 134)
This study examined the effects of short-term HIIT swimming on the GLUT4 content of skeletal muscle in rats. GLUT-4 is responsible for glucose uptake in skeletal muscles. The study used the Tabata Protocol (20 seconds sprint with 10 seconds rest) for 8 days of HIIT swimming. The study found that 8 days of HIIT lasting only 280 seconds elevated both GLUT4 content and maximal glucose transport activity similar to that obtained by a total of 6 hours of low-intensity training.
The Effect of High-Intensity Intermittent Exercise on the Body Composition of Overweight Young Men. Heydari et. al., 2012. (Cited by 130)
This study examined the effects of HIIT on total body, abdominal, trunk, visceral fat mass, and fat free mass of young overweight males. The participants were assigned to HIIT or control groups. The HIIT group protocol was 60 sets x 8 seconds of HIIT at 90% of HR peak with 12 seconds of rest in between each set, 3 times per week for 12 weeks. The study found that HIIT increased VO2peak and participants experienced significant weight loss (1.5kg) and a significant reduction in total fat mass (2kg) while maintaining or gaining lean muscle mass.
Interval training in the fed or fasted state improves body composition and muscle oxidative capacity in overweight women. Gillen et. al., 2013. (Cited by 104).
This study examined the effects of low-volume HIIT in the fasted versus fed state on body composition, muscle oxidative capacity, and glycemic control in overweight/obese women. The study assigned women to either the fasted or fed groups and both groups performed HIIT (10 sets x 60 seconds cycling at 90% HRmax with 60 seconds of recovery) 3 times per week for 6 weeks. The study found that HIIT is a time-efficient strategy to improve body composition and decreased fat in both the abdominal and leg region in as early as six weeks. However, fed versus fasted state HIIT did not cause any significant differences.
Where does HIT fit? An examination of the affective response to high-intensity intervals in comparison to continuous moderate-and continuous vigorous-intensity exercise in the exercise intensity-affect continuum. Jung et. al., 2014. (Cited by 63)
This study compared HIIT to continuous moderate-intensity exercise and continuous vigorous-intensity exercise. Continuous vigorous-intensity exercise has consistently caused more aversion than continuous moderate-intensity exercise. However, participants have reported greater enjoyment of HIIT as compared to continuous moderate intensity exercise and continuous vigorous intensity exercise with over 50% of participants reporting a preference to engage in HIIT.
Three Minutes of All-Out Intermittent Exercise per Week Increases Skeletal Muscle Oxidative Capacity and Improves Cardiometabolic Health. Gillen et. al., 2014. (Cited by 51)
This study examined whether a very low volume HIIT protocol work could increase skeletal muscle oxidative capacity and other health markers on overweight men and women. The study took place over 6 weeks with the HIIT protocol (2-minute warm-up, 3 sets x 20 seconds ‘all-out’ sprints on a cycling ergometer with 2 minutes of active recovery in between each set, and a 3-minute cool-down). The peak oxygen uptake increased by 12% and arterial pressure decreased by 7% after training. The study found that very low-volume HIIT (only 1 minute of intense exercise three times per week for six weeks) caused beneficial health adaptations in overweight adults.
Extremely low volume, whole-body aerobic-resistance training improves aerobic fitness and muscular endurance in females. McRae et. al. 2012. (Cited by 48)
This study compared the effect of body-weight HIIT to traditional ET in women. The participants completed 4 days of training per week doing either Tabata-Style HIIT (8 x 20 seconds of a single exercise of burpees, jumping jacks, mountain climbers, or squat thrusts separated by 10 seconds of rest). The study found that body-weight HIIT provide similar aerobic benefits to ET (30 minutes at 85% HRmax) and also improved muscular endurance.
Twelve weeks of Sprint Interval Training Improves Indices of Cardiometabolic Health Similar to Traditional Endurance Training Despite a Five-Fold Lower Exercise Volume and Time Commitment. Gillen et. al., 2016. (Cited by 48)
This is the study that has been popularized in the One-Minute Workout by Dr. Martin Gibala. The researchers examined whether SIT improved insulin sensitivity and other measures of cardiometabolic health similar to ET. The two exercise protocols were SIT (3 x 20 seconds all-out cycling sprints with 2 minutes of rest, 3 workouts/week for 12 weeks) and ET (45 minutes of continuous exercise at 70% of maximal heart rate 3 times/week for 12 weeks). Both exercise protocols included a 2-minute warm-up and 3-minute cool-down. The study concludes that 3 minutes of SIT per week was as effective as 150 minutes of ET per week for improving cardiorespiratory fitness, insulin sensitivity and mitochondrial activity in previously inactive men.
Why sprint interval training is inappropriate for a largely sedentary population. Hardcastle et. al. 2014. (Cited by 33).
This study provides a counter-argument to SIT stating that a largely sedentary population would not likely adopt SIT. The researchers contend that the prospect of participating in SIT for previously sedentary individuals is likely to be considered too difficult and may evoke anticipated perceived incompetence, lower self-esteem, and potential failure. They also state that the motivation and effort required to participate in high intensity exercise is much higher than that needed to undertake activities of a moderate to low intensity.
Commentary in Response. Jung et. al., 2016. (Cited by 7):
This response to the Hardcastle article states that continuous high-intensity exercise (high intensity for an extended period of time) cannot be equated to HIIT because HIIT provides recovery periods. If the intensity and frequency takes into account the participants background and are gradually increased, interval training won’t evoke perceptions of incompetence, low self-esteem, and potential failure.
Music enhances performance and perceived enjoyment of sprint interval training. Stork et. al., 2015. (Cited by 27)
This study examined whether listening to self-selected music can impact the motivation, performance and enjoyment of doing SIT. The study consisted of splitting participants into the music and non-music groups and conducting the Wingate Anaerobic Test (4-6 set of 30 seconds all-out cycling efforts including 4 minutes of rest between each set). The study found that the performance and perceived enjoyment of SIT exercise was higher in the music group.
The Effects of High Intensity Interval Training vs. Steady State Training on Aerobic and Anaerobic Capacity. Foster et. al., 2015. (Cited by 20)
This study compared the effects of HIIT (Tabata and Meyers protocols) to ET. The study used untrained individuals and showed that all groups improved their aerobic capacity and anaerobic capacity. The results of the training showed HIIT protocols are time efficient, but that Tabata may be less enjoyable than Meyers or steady-state cardio depending on the intensity and duration level even though all participants showed a decrease in enjoyment of the exercises.
Comparison of High-Intensity Interval Training and Moderate-to-Vigorous Continuous Training for Cardiometabolic Health and Exercise Enjoyment in Obese Young Women: A Randomized Controlled Trial. Kong et. al., 2016. (Cited by 10)
This study compared the effects of 5 weeks of HIIT against moderate to vigorous ET in obese young women. The participants in the HIIT group did a total of 20 minutes of exercises (intervals of 8 seconds of cycling and 12 seconds of rest for four days a week). The participants in the ET group did 40 minutes of continuous cycling at 60-80% of their Vo2peak for four days a week. The study found that short-interval HIIT improved cardiorespiratory health and was more enjoyable and time-efficient than ET for long term.
High-Intensity Interval Training Elicits Higher Enjoyment than Moderate Intensity Continuous Exercise. Thum et. al., 2017. (Cited by 2)
This study examined whether HIIT (8 intervals of 1 minute at 85% intensity with 1 minute of recovery) is more enjoyable than ET (20 minutes of cycling at 45% intensity). Enjoyment is important because exercise adherence is affected by factors including perceptions of enjoyment, time availability, and intrinsic motivation. The study found that 92% of the participants in their study preferred HIIT to ET. Although HIIT is more physically demanding than ET, individuals report greater enjoyment due to its time efficiency and constantly changing stimulus.