At Train Together, we let the research speak for itself. Check out the following studies that explain why HIIT training is superior to all other training methods.
A 2015 systematic review and meta-analysis of randomized controlled trials found that HIIT training and traditional endurance training both lead to significantly improved cardiovascular fitness in healthy adults ages 18–45 but greater improvements in VO2 max were seen in those participating in the HIIT exercise regimen. Another analysis also found that HIIT regimens of one month or longer effectively improve cardiovascular fitness in adolescents and lead to moderate improvements in body composition. Furthermore, a separate systematic review and meta-analysis of seven small randomized controlled trials found that HIIT (defined as four intervals of four minutes at 85–95% of max heart rate with three-minute intervals at 60–70% of max heart rate) was more effective than moderate-intensity continuous training at improving blood vessel function and markers of blood vessel health.
A 2015 meta-analysis comparing HIIT to moderate intensity continuous training (MICT) in people with coronary artery disease found that HIIT leads to greater improvements in VO2 max but that MICT leads to greater reductions in body weight and heart rate. A 2014 meta-analysis found that the cardiorespiratory fitness, as measured by VO2 max, of individuals with lifestyle-induced chronic cardiovascular or metabolic diseases (including high blood pressure, obesity, heart failure, coronary artery disease, or metabolic syndrome) who completed a HIIT exercise program was nearly double that of individuals who completed a MICT exercise program. In a study published out of Arizona State in 2018 found that, "HIIE protocols performed ∼18 h before ingestion of a high-energy fast food meal attenuated but did not entirely eliminate postprandial endothelial dysfunction in young men largely by improving fasting endothelial function." These findings suggest that HIIT training has a physiologically protective mechanism associated with it which can carry over into successive days of non-training.
HIIT significantly lowers insulin resistance compared to continuous training or control conditions and leads to modestly decreased fasting blood glucose levels and increased weight loss compared to those who do not undergo a physical activity intervention. Another study found that HIIT was more effective than moderate-intensity continuous training at fasting insulin levels (31% decrease and 9% decrease, respectively).
A 2007 study examined HIIT's physiological effects on fat oxidation in moderately active women. The participants in the study performed HIIT (defined as ten sets of 4-minute cycling bursts at an intensity of 90% VO2max separated by 2 minutes of rest) every other day over a 2-week period. The study found that 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. A 2010 systematic review of HIIT summarized the results of HIIT on fat loss and stated that HIIT can result in modest reductions of subcutaneous fat in young and healthy individuals, but greater reductions for overweight individuals.
A 2017 study examined the effect of HIIT on cognitive performance among a group of children (N=318). The authors show that HIIT is beneficial to cognitive control and working memory capacity when compared against "a blend of board games, computer games, and trivia quizzes" and that this effect is mediated by the BDNF polymorphism. They conclude that the study "suggests a promising alternative to enhance cognition, via short and potent exercise regimens".