The term HIIT (high intensity interval training ) is everywhere you look in the fitness industry . Your local gym will usually offer some form of a HIIT class and the world is full of enthusiasts sweating it out for 30-60 minutes in these groups . A format commonly seen in these sessions is the use of a "Tabata"- sometimes for an extended period of time.
The idea is that you do intervals of effort, then have an active rest period (that is low intensity exercise) or complete rest in some cases before recommencing the higher intensity physical effort. It does make you feel like you have been working hard BUT is it doing you any good?
What is the science behind HIIT workouts?
Well the bottom line is that they are a beneficial addition to your training program IF you do them a certain way. On the other hand , if done "incorrectly" they can actually contribute to over stressing the body , leading to a number of negative factors such as lethargy, weight gain, increased injury risk , and poor exercise performance.
So in this blog we are going to dig a bit deeper into HIIT and see how you can make this exercise format work best for you and your goals.
Let’s explore some of the terminology.
VO2 max is the maximum amount of oxygen a person utilises during physical exertion, and is a measure of cardiorespiratory fitness. As you age a higher VO2max is related to reduced morbidity and increased longevity. That is, it is a predictor of your HEALTHSPAN. The current World Health Organization recommendation is that individuals exercise for at least 150 minutes per week at 40-60% of VO2max or 75 minutes per week at 60-85% of VO2 max.
HIIT refers to exercising at greater than 85% of your VO2 max . That is "very hard " exertion. Most HIIT protocols in studies involve 10-16 mins of exercise . The recovery exercise is done at 20-40% VO2max- that is, light exercise. This is not to be confused with circuit training which involves varying exercises and rest periods, at varying intensity levels.
SIT (sprint interval training) is going as hard as you possibly can for the high intensity components of HIIT. This is extremely hard exercise and you would be working at levels over 100% of VO2 max, up to 250%. This sort of exercise can only be sustained for short duration and requires longer and complete recovery between efforts . The classic SIT protocol is 6 X 30 second all out sprints (bike, run, row, ski erg... you get the picture) , with a 4 minute complete rest period between each sprint.
MICT (moderate intensity continuous training) is training between 60-85% VO2max continuously for any given length of time.
MAF heart rate training maximum - as developed by Phil Maffertone, is 180 - your age (with additional specific adjustments depending on personal factors). He also talks about the Black Hole Training zone which is between the MAF maximum (which comes out to around your Aerobic Threshold, about 75% VO2 max for trained individuals) and the 85% VO2max. More on this later.
"Tabata" has been used interchangeably in many fitness facilities with HIIT or at least modified to the extent that it no longer resembles what its creators intended. The original protocol was named after Dr Izumi Tabata who developed it with the coach of the Japanese Olympic Speed Skating Team (coach Koichi). They studied the outcome in performance as measured by VO2 max and anaerobic capacity of the athletes when performing a 60min jog at 70% VO2max 5 days a week for 6 weeks vs the Tabata Protocol. The Tabata Protocol involved 4 minutes of 20 seconds at 170% VO2max (that is , very hard- as hard as you can go) followed by 10 seconds rest . All performed on a cycle ergometer.
So in fact this was a form of Sprint Interval Training. The outcome was that for just 4 minutes , 5 times a week, for 6 weeks the athletes could see VO2 max and anaerobic capacity improvements superior to that of the longer slower exercise. They were not measuring fat loss, or other health metrics.
So what does the science tell us about the benefits of these high intensity programs?
Overall, HIIT programs are as good or better at improving VO2max and anaerobic capacity than MICT.
HIIT in overweight/obese populations has been shown to reduce waist circumference, resting heart rate, percentage body fat, blood pressure and fasting glucose. All beneficial for overall health.
In populations with normal weight , a meta analysis of available studies failed to find any improvements in these risk markers (other than improvement in VO2max). However percentage lean muscle mass can be increased in all groups- another marker of HEALTHSPAN.
The results are similar for SIT and a study looking at VO2 max benefits for the average sedentary population suggests that 2-3 x 10-20 sec sprints with a 3min rest interval performed at slightly lower intensity (somewhat hard ) can create similar results . This protocol has been termed REHIT (reduced exertion high intensity exercise training) and in sedentary individuals can also demonstrate superior benefits in fitness, body composition and glucose metabolism than MICT.
Interestingly there is some evidence that if we go the other way and ramp up the number of sprint reps from the usual SIT protocol we see a reduced VO2max effect- not surprising really as this fits into our known MORE is NOT necessarily better adage when it comes to exercise (see my previous post ).
The benefits of the REHIT program is that for time poor individuals, benefits are seen with LESS than the WHO recommended time commitment to exercise. Normal HIIT or SIT protocols do not reduce the actual time commitment when we factor for rest periods.
What are the potential down sides of HIIT, SIT or REHIT?
From a risk perspective, there are potential issues with embarking directly into high intensity exercise without some screening. It is advised all participants are screened before participation, using the tool relevant to their country (eg ACSM screening tool in the USA or APSS in Australia).
Although studies have taken screened untrained individuals directly into such protocols , I would advise getting a baseline fitness first before experimenting with the high intensity stuff. It is a lot less daunting and reduces injury risk.
The biggest issue with these programs is when they are implemented incorrectly. Particularly when people are encouraged to do "max efforts" for unrealistic durations. As the appropriate heart rates are unsustainable , you will tend to fall into that black hole training zone between the MAF maximum and the 85% VO2 max level. Exercising at these heart rates for extended periods has potential negative effects on your heart and your metabolism such that although we may get fitter we may not be healthier (see post). You will also not be reaping the benefits of true high intensity or sprint training as you are performing the efforts at lower intensity than intended.
How can you best use HIIT, SIT or REHIT when looking to keep up your outdoor adventures into your 50s, 60s, 70s, and even 80s?
1/ The ideal approach is to keep moving in your daily life as much as possible at any intensity.
2/ Aim for some MICT below MAF maximum heart rate , but above 60% VO2max for 75 minutes per week.
(so that would equate to 3 x 30 min sessions).
3/ Do one SIT session every 7 -10 days to get the hormonal and fitness inducing boost with sufficient recovery before the next high intensity session. Be it a beach sprint session, a stationary bike or row , a ski erg: do short all out sprints for 4-6 reps of 20-30s duration with prolonged rest - 3 mins between each sprint.
4/ And ditch the distorted Tabatas, HIITS and SITS which don't meet the correct parameters.
Certainly if you're training for fitness and can factor in good recovery for the remainder of your day you could do proper Tabata 5 days a week for 6 weeks as the olympic athletes did. Most of us aren't full time athletes though and we can't adequately recover from lots of high intensity exercise sufficiently. Hence we risk overreaching with its reduction in performance.
If you are time poor, have a lot of trouble meeting the WHO minimum guidelines for your weekly exercise quota, and are looking to improve some health metrics ( and here is a great coaching conversation waiting to be had)- you may want to think about the REHIT approach .
THE BOTTOM LINE HERE IS TO CONSIDER ADDING A PROPER HIIT OR SIT SESSION INTO YOUR EXERCISE PROGRAM. IT WILL HELP IMPROVE YOUR OVERALL FITNESS AND HEALTH AND CONTRIBUTE TO KEEPING YOU ON THE SNOW , IN THE SURF OR OUT IN THE HILLS NO MATTER WHAT YOUR AGE.
If you need any help achieving your health and fitness goals and want to keep skiing, surfing, hiking or snowboarding as you get older reach out to Primal Regeneration . I offer Health Coaching specialising in these areas . My background as doctor, Primal Health and Fitness Coach, ski coach and surfer all contribute to my ability to help you on your journey.
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