Written By: Dan DeBruyne, Msc PT, BA Kin
Time - it is the one thing that we all have the same amount of. Everyone gets 24 hours, 1440 minutes, 86400 seconds per day. It is also one of the most common barriers that people cite when asked what stops them from exercising (Sallis and Hovell, 1990; Sallis et al., 1992). This is consistent across all demographics worldwide . We all want to be as efficient as possible with our time, especially when it comes to fitness. For many of us the idea of going to the gym for a couple hours sounds time-consuming, boring and downright impossible to fit into our schedule.
You are not alone in this line of thinking, in fact, people have been looking for ways to maximize the their workouts benefits while minimize their time for years. One of the techniques created for this purpose is high intensity interval training. High intensity interval training or HIIT is roughly defined as a short amount of near maximal effort exercise - followed by a moderate or low effort exercise recovery time - repeated for multiple bouts.
High intensity interval training is found in exercise regimens like Tabata, Crossfit, Fartlek, and the Peter Coe Method among others. Since its inception in the 1970’s this exercise method has morphed many times but at its core follows the same principles of high-speed/high effort, followed by low to moderate speed/effort to recover.
The science behind the method is that by working at your body’s maximal cardiovascular capacity you improve the metabolism of your muscles. This improves their efficiency at accepting oxygen from the bloodstream and clearing out various waste products that build up during exercise. These metabolic adaptations can then improve your ability to perform at lower thresholds (ie: a light jog). Think of it like working out any other muscle group in the body - if you’ve worked up to squatting 200 lbs - then moving 20lbs should be a piece of cake. Except instead of massive thighs you end up with a totally ripped cardiovascular system (not as easy to appreciate in the mirror, but impressive nonetheless). The difference between conventional weight training and HIIT is that the cardiovascular system adapts much quicker to stimulus then skeletal muscle. This means that positive changes from HIIT training can show up in as little as 2 weeks of regular high-intensity interval training while changes in muscle size won’t show up until 6 weeks of conventional weight training.
A 2015 meta-analysis (that is a study that combines multiple studies to create a summary of the research) found that persons aged 18-45 cardiovascular fitness and cycling endurance increased with both low intensity steady training and high-intensity interval training. The major difference between the two was that the VO2 Max scores were higher in the HIIT groups. Without getting too technical, your VO2 max is an indicator of how well your body can take in oxygen and remove waste products from your muscles during cardiovascular exercise (Ramos et al. 2015).
Numerous studies have documented adaptations similar to that of endurance training including increased resting glycogen content (how much energy is being stored in your muscles), reduced rate of glycogen utilization and lactate production (improved muscle efficiency), increased muscle lipid oxidation (fat burning), improved vascularization (bloodflow) to extremities, improved insulin sensitivity (important for prevention of type 2 diabetes), as well as subjects’ improved exercise performance. (Burgomaster et al. 2005, 2008; Gibala et al. 2006; Rakobowchuk et al. 2008).
Other research has also indicated that patient enjoyment and involvement is increased in comparison to moderate intensity or low intensity exercise (Bartlett et al. 2011). Which makes sense when we consider it takes less time, requires more focus and requires us to truly work hard.
So I know the question on the tip of your tongue… how little can I get away with?
Well, to improve cardiovascular fitness, insulin sensitivity, and exercise capacity most research had individuals performing 2-3 sessions a week with 4-6 sprints lasting 30 seconds at 90-100% of the persons maximal capacity, interspersed with 4 minutes of low-to-moderate (~60%) cycling. For a total of 14 minutes per session or 28 minutes per week. But this type of training doesn’t just have to be sprints or cycling - there are many ways to incorporate this into your training sessions and or core workouts - such as sled pulls/pushes, kettlebell swings, press-ups, jump squats, body weight squats, rowing ergometers, speed walking, skipping, assault bikes etc. Anything that gets you breathing hard and can be sustained for ~30 seconds at a maximal effort.
**Caveat - if you have any cardiovascular issues, blood pressure concerns, breathing issues, recent surgery or any other major health concerns - it is advised that you see a healthcare professional prior to starting a HIIT program. **
As always if you are unsure, injured or just want more information before beginning your own high-intensity training, get connected with your local professional and go from there.
Ramos, J. S., Dalleck, L. C., Tjonna, A. E., Beetham, K. S., & Coombes, J. S. (2015). The impact of high-intensity interval training versus moderate-intensity continuous training on vascular function: a systematic review and meta-analysis. Sports Medicine, 45(5), 679-692.
Bartlett JD, Close GL, MacLaren DP, Gregson W, Drust B & Morton JP (2011). High‐intensity interval running is perceived to be more enjoyable than moderate‐intensity continuous exercise: implications for exercise adherence. J Sports Sci 29, 547–553.
Burgomaster KA, Howarth KR, Phillips SM, Rakobowchuk M, Macdonald MJ, McGee SL & Gibala MJ (2008). Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans. J Physiol 586, 151–160.
Burgomaster KA, Hughes SC, Heigenhauser GJ, Bradwell SN & Gibala MJ (2005). Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans. J Appl Physiol 98, 1985–1990.
Egan B, Carson BP, Garcia‐Roves PM, Chibalin AV, Sarsfield FM, Barron N, McCaffrey N, Moyna NM, Zierath JR & O’Gorman DJ (2010). Exercise intensity‐dependent regulation of PGC‐1α mRNA abundance is associated with differential activation of upstream signalling kinases in human skeletal muscle. J Physiol 588, 1779–1790.
Gibala MJ & McGee SL (2008). Metabolic adaptations to short‐term high‐intensity interval training: a little pain for a lot of gain? Exerc Sport Sci Rev 36, 58–63.
Gibala MJ, Little JP, van Essen M, Wilkin GP, Burgomaster KA, Safdar A, Raha S & Tarnopolsky MA (2006). Short‐term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. J Physiol 575, 901–911.
Jelleyman, C. , Yates, T. , O'Donovan, G. , Gray, L. J., King, J. A., Khunti, K. and Davies, M. J. (2015), The effects of HIIT on metabolic health. Obes Rev, 16: 942-961. doi:10.1111/obr.12317
Content in the “Personal Barriers” section was taken from Promoting Physical Activity: A Guide for Community Action (USDHHS, 1999).