High Intensity Interval Training

It is now well established that high-intensity interval training (HIIT) induces numerous physiological adaptations that resemble traditional endurance training despite a dramatically lower total exercise volume¹. In addition to using tests such as cycling time trials, scientists have also confirmed the efficacy of high intensity interval training by measuring the changes in expression of specific proteins that are tied to aerobic capacity^{1, 2}. In science, once you have a theory that can be confirmed in practice and also explained by a specific mechanism – then you can pretty much call it a scientific fact.

What Is High Intensity Interval Training

In scientific circles, HIIT typically encompasses all-out sprints of 30 seconds followed by a rest period of 4 minutes before the cycle is repeated again another 3-5 times within the one session¹. This test, which is normally performed on a specialised stationary bicycle (i.e. ergometer) to measures an individual’s power output, is commonly referred to as the Wingate test. High intensity interval training has many other names:

• Short-term sprint interval training³
• Short-term high intensity interval training⁴
• High-intensity sprint interval training³
• Low-volume high intensity interval training⁵

Benefits of High Intensity Interval Training

The most intriguing and exciting aspect of HIIT is that the volume of exercise and time spent training is typically in the order of 75-90% lower⁶. ‘Lack of time’ is the most commonly cited barrier to performing regular exercise for a variety of populations. So naturally, HIIT has attracted a lot of interest in the scientific community. The table below provides an example of the contrasting time commitments for a HIIT program versus a more traditional endurance training program over two weeks.

Parameter	High Intensity Interval Training	Endurance Training
Work intensity	‘All out’ supramaximal	65% VO2peak
Exercise protocol (per session)	30 s x 4-6 repeats, 4 min recovery	90-120 min of continuous exercise
Total exercise/training time commitment per session	2-3 min (intervals only) 18-27 min (incl. recovery)	90-120 min
Total exercise/training time commitment over 2 weeks	15 min (intervals only) 135 min (incl. recovery)	630 min
Total exercise volume over 2 weeks	~630 kJ (intervals only) ~950 kJ (incl. recovery)	~6500 kJ

* Gibala MJ, et al. Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. J Physiol. 2006;575(3):901–911.

HIIT may also be more effective than traditional endurance training for improving other important determinants of endurance performance, such as muscle buffering capacity⁷. HIIT has also been shown to improve insulin sensitivity^{8, 9}. Other benefits include⁵:

• Increased resting glycogen content
• Reduced rate of glycogen utilisation and lactate production
• Increased capacity for whole-body and skeletal muscle lipid oxidation
• Enhanced peripheral vascular structure and function
• Improved exercise performance as measured by time-to-exhaustion tests
• Increased maximal oxygen uptake

Variations on Traditional High Intensity Interval Training

A number of variations on HIIT have been explored and confirmed to be equally effective as the traditional Wingate test. One example is an 8-second cycle sprint followed by 12 s of low intensity cycling for a period of 20 min¹⁰. Thus, instead of 4 to 6 sprints per session, as used in Wingate protocol studies, subjects using the 8 s/12 s protocol sprint 60 times at lower exercise intensity. Total sprint time is 8min with 12 min of low intensity cycling. A couple of other studies have successfully used slight variations on this protocol, such as a 12 s sprint/24 s recovery¹¹ or 24 s sprint/36 s recovery¹². Another more recent study used sessions consisting of 8-12 x 60 s intervals at 100% of peak power, separated by 75 s of recovery. While this study did not involve a control group, the subjects that completed the training showed skeletal muscle metabolic and performance adaptations consistent with traditional ‘endurance’ training⁶.

So in summary, the science is pretty conclusive that HIIT is a potent, time-efficient form of exercise to increase both anaerobic and aerobic capacity. Recent research suggests the traditional model of HIIT can be varied substantially, with minimal loss of its efficacy. The most important elements are repeated short bouts of a high intensity. So go ahead and use your imagination to make your own HIIT routine and start reaping the rewards from more time and better conditioning.

1. Burgomaster KA, et al. Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans. J Physiol.2008;586(1):151–160.
2. Gibala MJ, et al. Effect of high-intensity interval exercise on signalling proteins involved in skeletal muscle remodelling in humans. Appl Physiol Nutr Metab. 2006;31:S37.
3. Gibala MJ, et al. Short-term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. J Physiol. 2006;575(3):901–911.
4. Forbes SC, et al. Short-term high-intensity interval training improves phosphocreatine recovery kinetics following moderate-intensity exercise in humans. Appl Physiol Nutr Metab. 2008;33:1124–1131.
5. Gibala MJ, et al. Physiological adaptations to low-volume, high-intensity interval training in health and disease. J Physiol. 2012;590(5):1077-1084.
6. Little JP, et al. A practical model of low-volume high-intensity interval training induces mitochondrial biogenesis in human skeletal muscle: potential mechanisms. Journal of Physiology. 2010;588(6):1011–1022.
7. Weston AR, et al. Skeletal muscle buffering capacity and endurance performance after high-intensity interval training by well-trained cyclists. Eur J Appl Physiol Occup Physiol. 1997;75: 7–13.
8. Babraj JA, et al. Extremely short duration high intensity interval training substantially improves insulin action in young healthy males. BMC Endocr Disord. 2009;9:3.
9. Richards JC, et al. Short-term sprint interval training increases insulin sensitivity in healthy adults but does not affect the thermogenic response to beta-adrenergic stimulation. J Physiol. 2010;588(Pt 15):2961-2972.
10. Trapp EG, et al. The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women. International Journal of Obesity. 2008;32(4):684–691.
11. Trapp EG, et al. Metabolic response of trained and untrained women during high-intensity intermittent cycle exercise. American Journal of Physiology. 2007;293(6):R2370–R2375.
12. Christmass MA, et al. Effect of work and recovery duration on skeletal muscle oxygenation and fuel use during sustained intermittent exercise. European Journal of Applied Physiology and Occupational Physiology. 1999;80(5):436–447