Studies by Tabata and others have explored the effectiveness of this method compared to traditional endurance training methods. A 2008 study by Gibala et al. demonstrated 2.5 hours of sprint interval training produced similar biochemical muscle changes to 10.5 hours of endurance training and similar endurance performance benefits. According to a study by King, HIIT increases the resting metabolic rate (RMR) for the following 24 hours due to excess post-exercise oxygen consumption, and may improve maximal oxygen consumption (VO2 max) more effectively than doing only traditional, long aerobic workout.Tabata’s 1997 study concluded that “intermittent exercise defined by the IE1 protocol may tax both the anaerobic and aerobic energy releasing systems almost maximally.” Around 20% of participants in Timmons’ 2010 study showed less than 5% improvement in aerobic capacity. Conversely, about 20% of participants were described as “high-responders”. A complex mixture of genes are involved, but differences in 11 single-nucleotide polymorphisms alone could predict 23% of the total variance in VO2max. Timmons was able to demonstrate that about half of the responsiveness of aerobic capacity to HIIT was genetically determined.
High-intensity interval training has also been shown to improve athletic performance. For already well-trained athletes, improvements in performance become difficult to attain; increases in training volume may yield no improvements. Previous research would suggest that, for athletes who are already well-trained, improvements in endurance performance can be achieved through high-intensity interval training. A 2009 study by Driller and co-workers showed an 8.2 second improvement in 2000m rowing time following 4 weeks of HIIT in well-trained rowers. This equates to a significant 2% improvement after just 7 interval-training sessions. The interval-training used by Driller and colleagues involved eight 2.5 minute work bouts at 90% of vVO2max, separated by individualized recovery intervals.