By Richard Roberts,
It seems as though with every passing year, we expect to fit more and more into our daily schedule. Work responsibilities, family matters and financial stress are at the forefront of our lives, and this may result in us neglecting our own physical health. Daily exercise is beneficial in many ways, but conventional cardiovascular workouts requiring an hour on the treadmill, elliptical trainer, or stationary bike may take time that simply isn’t there. And you’re not alone – inability to make a time commitment is often described as the largest barrier to exercise (1). Not to worry though – a form of exercise called high-intensity interval training (HIIT) may be a suitable solution.
High-intensity interval training is characterized by numerous short-lived periods of intense exertion, performed within a longer period of low-intensity “resting” exercise (2). Exercise intensity during HIIT workouts is often calculated as a proportion of maximum heart rate (maximum beats per minute = 211 – 0.64 x age) (4). A 2015 study by Ramos et al. cite this HIIT workout, taking less than thirty minutes per session: “four intervals of four minutes (HIIT) at 85-95% heart rate maximum, interspersed with three minutes of active recovery at 60-70% heart rate maximum […] three times per week”(5). Over the course of twelve weeks, athletes completing this training plan showed larger improvements in general vascular function, as shown by the amount of dilation of a major artery in response to heightened blood flow, compared to athletes completing a moderate intensity continuous training (MICT) program. The MICT program was similar to conventional aerobic training – long (30+ minutes) in duration, and less vigorous in exertion(5). These larger improvements were seen even though the HIIT athletes had lower weekly training time commitments and lower weekly calorie expenditure during training.
Maximal bodily oxygen consumption (VO2max) is considered to be a primary indicator of endurance-based fitness, rather than strength or power-based fitness, in an athlete. A meta-analysis by Milanovic et al. concluded that HIIT alone results in substantial increases in VO2max, dismissing the idea that HIIT must be supplemented with less intense workouts for beneficial cardiovascular effects. Furthermore, they concluded that these effects were larger in younger subjects as well as in subjects with lower baseline fitness levels (3). These benefits are important to consider for individuals who feel pressured to commit to lengthy workouts, and instead opt out completely.
Alongside its clear benefits to physical fitness, HIIT has also shown a greater ability to positively impact cardiovascular disease risk factors, including significantly decreasing systolic blood pressure, levels of low-density lipoprotein “bad cholesterol” in the blood, and signs of oxidative damage to DNA, proteins and membranes. HIIT may further benefit individuals with type II diabetes, as it has shown to increase insulin sensitivity as well as decrease waist-to-hip ratio, a general measure of health, more than MICT. Lastly, low-volume HIIT protocols like the Wingate protocol (60 seconds “all out”, 4.5 minute rest, 4-6 sets) have been shown to increase levels of the antibody PGC-1α several-fold when measured three hours after exercise (1). PGC-1α regulates bodily carbohydrate and lipid metabolism, as well as stimulates the remodeling of muscles so that they can consume more oxygen effectively. This may be one factor that helps to explain how HIIT can increase bodily oxygen consumption in response to exercise.
It is important to understand that some forms of HIIT are extremely physically demanding. Certain demographics are generally more at risk to adverse cardiovascular events –including patients currently undergoing cardiac rehabilitation for surgery or patients with chronic cardiovascular disease –and should be wary of safety when completing HIIT workouts. In patients with coronary heart disease, Ribero et al. advise shorter HIIT intervals for patients with less baseline aerobic fitness and medium to long intervals for patients with higher aerobic fitness (6). However, they recommend that individualized models of exercise should be considered. This recommendation can be adopted to any athlete, healthy or otherwise, and should be considered for athletes new to HIIT due to natural variation in exercise physiology between individuals.
HIIT training, while new to many people, touts numerous benefits that move beyond simple markers of physical fitness. Many studies mention the need for additional, more expansive studies to further cement the effects of HIIT on lipid composition in the blood and on neuromuscular conductivity, however it is clear that for the busy athlete, HIIT is an effective training strategy to increase cardiovascular health with a decreased time commitment.
- Gibala MJ, Little JP, MacDonald MJ, Hawley JA. Physiological adaptations to low-volume, high-intensity interval training in health and disease. J Physiol 590: 1077–1084, 2012.
- Kravitz L. High-intensity interval training. 2014.
- Milanović Z, Sporiš G, Weston M. Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials. Sports Med 45: 1469–81, 2015.
- Nes BM, Janszky I, Wisløff U, Støylen A, Karlsen T. Age-predicted maximal heart rate in healthy subjects: The HUNT fitness study. Scand J Med Sci Sports 23: 697–704, 2013.
- Ramos JS, Dalleck LC, Tjonna AE, Beetham KS, Coombes JS. The Impact of High-Intensity Interval Training Versus Moderate-Intensity Continuous Training on Vascular Function: a Systematic Review and Meta-Analysis. Sport Med 45: 679–692, 2015.
- Ribeiro PAB, Boidin M, Juneau M, Nigam A, Gayda M. High-intensity interval training in patients with coronary heart disease: Prescription models and perspectives. Ann. Phys. Rehabil. Med. (2016). doi: 10.1016/j.rehab.2016.04.004.