HIT me with your rhythm sticks… wait, what is HIT?
HIT or High Intensity Training (sometimes with double ‘I’s: HIIT High Intensity Interval Training) is quickly becoming a ubiquitous phrase for anyone interested in improving their fitness. Brought to living rooms around the UK by Michael Moseley’s Horizon for the BBC in 2012, no gym class programme seems to be complete without a HIT session and specialist HIT studios are popping up around the capital. It’s a big topic so this is the first in a series of posts looking at what it is, how it applies to you as well as common misconceptions.
So what is all the fuss about? And who can benefit from it?
HIT training is not an especially new concept – one of it’s earliest subjects was the young Seb Coe in the 1970s and one of the first major pieces of research was published in 19971. As interest in the subject has increased and more research has been published, the media and fitness industry has been giving increasing attention to a training approach that promises remarkable improvements from micro-doses of training. In fact, in a recent survey by ACSM, HIT training shot up the rankings to number three in the top fitness industry trends for 20162, so interest is set to grow.
The original HIT protocol designed by Izumi Tabata was conducted on stationary bikes and the athletes being studied were elite speed skaters. The athletes in the study performed 6-7 x 20 second maximal efforts with just 10 seconds of rest between them, 4 times per week for 6 weeks (the protocol developed following the study is 8 intervals of 20 seconds work and 10 seconds rest, 4 minutes in total). Of course each workout was topped-and-tailed with a gradual warm-up and cool-down. The study found that this particular protocol worked both the aerobic and anaerobic systems to their maximum capacities. By the end of the 6-week study, the athletes following the protocol increased their VO2 Max by 13% compared to the control group who performed longer intervals with much more recovery.
How does it work?
Working well above your VO2 Max means that your muscles demand more oxygen than your respiratory and circulatory systems are able to deliver, which means your muscles have no choice but to use their glycogen stores to produce energy anaerobically. To understand why this happens, it’s helpful to understand how the body uses energy at high intensities. There are two forms of anaerobic energy production; the lactic acid system, which relies on the recycling of lactic acid and sustains high intensity effort for a couple of minutes on it’s own; the second is the creatine-phosphate system which can bring about very strong muscle contractions but only for about 10 seconds and requires a couple of minutes recovery before the effort can be repeated.
Compared to conventional speed training which works almost exclusively in the anaerobic zone, facilitated by long recovery periods between work intervals, Tabata’s short recoveries of 10 seconds do not allow the creatine phosphate energy systems to restock in time for the next interval, which means there is no assistance from creatine phosphate after the first interval and as the heart rate edges higher above the lactate threshold, leaving the lactic acid and aerobic energy systems working as hard as they can to sustain the intervals. This means that even though Tabata intervals are at lower intensities than pure anaerobic speed intervals in terms of VO2 Max, the lactic acid system has to work harder due to the insufficient recovery periods. That is to say, the system is put under greater strain in 4 minutes than a longer, higher intensity session with more rest. The added benefit to to body composition is that taking the body’s energy systems to maximum capacity results in elevated energy consumption in the hours following the session – the much-sought-after EPOC effect or ‘afterburn’.
What this means for training is summarised neatly by Raphael Brandon in Peak Performance3, who argues a combination of approaches optimised to meet the goals of the athlete is the most effective strategy. Conventional sprint intervals are effective for improving the ability to sprint repeatedly over the course of a match recovering as much as possible between efforts, whereas the short intervals with insufficient recovery that characterise the Tabata protocol can stimulate improvements in anaerobic capacity exceeding those that can be achieved with sprint intervals alone. A footballer would spend more time working on the former whereas a 1500m runner would focus more of their training on the latter, though clearly there are benefits to incorporating both approaches to an extent.
Following the initial results seen in Tabata’s study, other physiologists have been keen to understand how similar approaches can be used to bring about health and fitness benefits which are not necessarily about pure athletic performance. Dozens of studies have been conducted in the years since Tabata’s research was first published, which led to Michael Mosely focussing on how ordinary people can benefit from short bursts of exercise in his Horizon programme.
Stay tuned for my next post where I’ll look in more detail at how non-elite athletes can reap health and fitness benefits from short bursts of training – click the ‘FOLLOW’ button on the right-hand side to get an email when the next post goes live.
- Tabata I, Irisawa K, Kouzaki M, Nishimura K, Ogita F, Miyachi M. Metabolic profile of high intensity intermittent exercises. Med. Sci. Sport Exerc. 1997;29:390–395. http://www.ncbi.nlm.nih.gov/pubmed/9139179 Accessed 17/11/2015.
- Thompson, Walter R. Ph.D., FACSM, WORLDWIDE SURVEY OF FITNESS TRENDS FOR 2016: 10th Anniversary Edition, ACSM’s Health & Fitness Journal, November/December 2015 Vol. 19 – Issue 6: p 9–18, http://mobile.journals.lww.com/acsm-healthfitness/_layouts/oaks.journals.mobile/articleviewer.aspx?year=2015&issue=11000&article=00005 accessed 17/11/2015
- Brandon, R., Aerobic system: interval training to improve fitness, Peak Performance, http://www.pponline.co.uk/encyc/aerobic-system-interval-training-to-improve-fitness-643# accessed 17/11/2015