Part 2 and Part 3 discussed the evidence for the many benefits of HIIT, but if you’re reading this, I’m assuming you’re keen to give it a go.
HIIT, despite the name, has been used in people recovering from heart surgery all the way to elite athletes. That’s because it’s the number one way to build cardiorespiratory fitness (see Part 2).
That said, you should get the all-clear from your doctor before taking up an exercise programme. Ideally, that would involve an ECG/EKG monitored exercise stress test, which would also give you an accurate maximum heart rate to work with.
If you do have a known heart problem, it’s best to do intense exercise under professional supervision.
That out of the way, let’s address some key questions when thinking about designing an effective HIIT programme for health.
The Faces of FITT
The American College of Sports Medicine uses the acronym FITT to describe the key characteristics of exercise that are important for making progress.
F.I.T.T. stands for Frequency, Intensity, Time, and Type. These are explained in the first video of our Move 101 series here.
In this case, frequency refers to how often you do a HIIT session in a week. Intensity is already set (see below). Time refers to both the duration of the interval and how many intervals in total (discussed below). And Type is already determined as HIIT.
What kind of activities can I do as HIIT?
Although HIIT in commercial programmes is often done using various bodyweight movements, i.e. calisthenics, the studies done to date and discussed in Parts 2 and 3 never assessed calisthenics.
Most studies done to date, at least in people with medical conditions and even just none-athletes, have been done using stationary bikes, treadmills, and occasionally running on a track or swimming.
As the goal of HIIT is to drive up heart rate, it’s best to use activities that use a lot of muscle, e.g. walking/running, cycling, swimming, or rowing. These can also be done indoors using equipment such as treadmills, stepmills, steppers, cross-trainers/ellipticals, rowing machines etc. If using your legs is out, permanently or temporarily, you can also use a hand bike.
Because I work mainly with people who have some kind of health issue, I usually prefer low impact options that are very low injury risk, so in most cases nothing beats a stationary bike, either upright or if that’s a problem, recumbent.
Outside of that, treadmills are handy, but instead of running just keep to a fast walk but increase the incline. The thing to avoid is holding onto the rails as this changes a natural activity of walking into a strange ineffective leg swinging exercise.
If you aren’t yet secure enough and need to hold on, use the side rails not the front. Using the side will make it more difficult to drag yourself along with your arms while essentially stumbling forwards – something I see a lot of people in commercial gyms do.
If you go the outdoor route, I’d also recommend picking a hill to walk up fast instead of running.
Most gyms I know don’t have stepmills, but if you have access to one, then I recommend them as long as the step height is reasonably comfortable for you. Stair climbing is a great exercise to build cardiovascular fitness and strength in the muscles of the legs and buttocks.
Basically, you want to choose one or more exercises that allow you to maintain some quality in your movement even as you push yourself hard. The more technical the movement, the more difficult that will be.
How long should an interval be?
In Part 1 I noted that HIIT comes in two broad categories, one that involves high but below maximum intensity for roughly 1-4 minutes, and all-out (maximum) efforts of 30 seconds or less often called sprint interval training (SIT).
SIT has been tested almost exclusively in healthy, usually athletic groups, so it’s general safety record in other groups is not well establish. Such all out efforts can put the heart under considerable strain and increase blood pressure rapidly.
The prudent approach is to keep intensity high, but not maximal and instead use intervals of 1-4 minutes. We’ll cover this a little more under the topic of progression below.
You can get special interval timers, use a smartphone app, or stick to simply using a watch or clock.
The question is more flexible if phrased in terms of how much total time should be spent at high-intensity. The answer being 10–20 minutes.
The less fit someone is to begin with, the more inclined I’d be to start at the 10 minute end of that range. In practice, that might mean doing 10 one minute intervals, or 5 two minute intervals.
One option that is also available is to have the intervals be different lengths. As the intention of HIIT training is to keep the heart rate high, arranging your intervals so you spend maximum time in your target range is a smart thing to do.
Heart rate doesn’t jump the instant you apply effort. It’s a lot like a car, even when you put the pedal to the metal, it takes time to reach top speed. A high performance body just like a high performance car will accelerate faster, but it’s never instant.
In my research with people who have non-alcoholic fatty liver (1), volunteers started with two minute intervals and it often took until late in the third or fourth interval for the heart rate to be in the desired range.
One way around this is to go from longer to shorter intervals, e.g. 4 minutes, then 3 minutes, then 2 minutes, and finally 1 minute. This gives 10 minutes in total.
How long should the recovery periods be?
The whole point of HIIT is that it allows people who couldn’t do more than a few minutes of high-intensity activity at a time to accumulate 10-20 minutes at high intensity.
The way to do this is to break up those 10-20 minutes into shorter intervals with a recovery period in-between. Those recovery periods can involve either complete rest, or some lower-intensity activity.
If you opt for the latter, which we’ll call active recovery, you have the option of staying with the exercise you’re using for the intervals, e.g. cycling, or doing something else.
That something else is extremely versatile, you could for example do some stretching or mobility work, visit our Move Better video library for some ideas.
Whatever you choose, the recovery period should allow you to catch your breath, have a sip of water, and let your heart rate come back down somewhat.
That still begs the question of how long? As long as it takes for you to repeat your effort in the preceding interval and no longer. That’s in theory anyway. In practice you have a few options:
- Recover for a set time. Most often that involves a recovery period roughly as long as the interval. That might mean 1 minute intervals separated by 1 minute recovery periods. You may prefer to start with longer recovery periods than intervals at first.
- Use the Perceived Recovery Status Scale (download here) to help guide you (2). When you would rate your recovery around 5 or 6, do the next interval.
- Use a heart rate monitor and when you’re heart rate drops below a certain target, do your next interval. That target can be somewhere between 60% and 70% of your maximum heart rate.
We’ll look at the most important ins and outs of heart rate in a future blog.
How intense should intervals be?
We discussed this in Part 1, but to recap – contrary to how HIIT programmes/protocols are often described, heart rate targets are not very practical. Go with Ratings of Perceived Exertion (download here) (2).
Using the scale, and interval should feel in 16-17 (meaning very hard).
The saying It never gets easier, you just get better applies here, so even though you might find you have to slow down during an interval, the whole interval should be a very hard effort.
Remember, you have a recovery period just around the corner.
Always start your exercise session with a warmup where you go from an intensity of about 9 (meaning very light) in the first minute or so, up to a 13 (meaning somewhat hard) in the last minute of the warmup.
Typical warmups are for five minutes, but there is nothing magic about that number, so feel free to go up to 10 minutes if it makes you feel more ready.
Going much above 10 minutes may take energy away from your intervals, so the idea is to warmup just enough to give a good effort when you launch straight into your first interval.
Exercise like medication has a dose, and that dose needs to be appropriate to your needs. That topic is covered in more detail in the second video of our Move 101 series here.
Exercise dose can’t be measured as conveniently as the dose of a drug as it’s really a product of FITT – frequency, intensity, time, and type.
Nonetheless, if one or more of these parameters increases, e.g. you do more sessions per week, more intervals in a session, longer intervals, or even decrease your recovery periods, then you’ve increased the dose of exercise.
That’s assuming you don’t cut back elsewhere, e.g. more intervals but shorter times. To be an increase in dose you have to be either doing more work in total, or the same amount of work in less time.
If we accept that exercise has a dose, then it should make sense that if we want to keep improving over time, we have to adjust that dose accordingly.
Another word for it would be progression. You need to make progress in your exercise to keep making progress in your health. Although there is a point where physical performance and health no longer travel in parallel, most of us aren’t anywhere near that point, so greater fitness equals better health prospects as long as we give our bodies enough time to adapt.
We exercise to make out bodies change, but our bodies want to conserve resources, so they only change as much as they feel is necessary given what we expose them to. That means if we don’t increase exercise dose as we get fitter, we’ll stop getting fitter.
So how can you gradually increase the dose? I gave some examples above, but lets be systematic about it.
Some progress is actually built in when we set an intensity. Recall from Part 1 that intensity is relative to your personal capacity. That means that as you get fitter, the amount of work you do, e.g. how far you cycle, swim, walk etc. during a given interval will increase if you are working at a given capacity, e.g. 85% of your maximum.
That’s why I recommend giving yourself at least three consecutive sessions and up to six, so 1-2 weeks, in which you make no intentional changes to your HIIT sessions. Keep all aspects of FITT the same.
Over time though, aim to progress from 10 minutes worth of intervals to 20. That might mean adding an extra 10 seconds per interval per week or fortnight.
Alternatively, add intervals. E.g. go from 10 intervals of one minute to 11 intervals, and then 12, and so on until you’re doing 20 one minute intervals.
Once you’ve reached 20 minutes, work on decreasing the rest time. That said, keep each interval to four minutes or less, and keep the recovery period long enough
Our bodies do get fairly efficient at activities we do often, and when it comes to exercise for health and or fat reduction, it’s actually good to do things we aren’t super efficient at because the greater efficiency equals less energy used for a given amount of work.
That means when you’ve reached your 20 minutes of accumulated high intensity activity per HIIT session, and your total recovery time is in the 10-15 minute range, it’s time to switch activity, e.g. from cycling to incline walking, or rowing.
How frequently should you do HIIT?
Preferably no more than two days in a row as immune cells start to decrease with multiple consecutive sessions (3). High-intensity exercise by its nature takes longer to recover from than low-to-moderate intensity physical activity.
On the other hand, as we found out in Part 2, some of the positive effects of HIIT, notably improved glucose control, tends to wear off after 48 hours.
If you are mostly or exclusively doing HIIT as exercise, then optimal is every other day, or if it’s more practical go for three times a week, but preferably with a 48 hour break in-between sessions.
If you do other forms of exercise, e.g. resistance training, you have the choice of combining the two training styles into a single session or have them on separate days.
There are no hard and fast rules here. But if I had to make a recommendation, I’d go with two HIIT sessions per week and 2 resistance exercise sessions. Or, three sessions combining both with the resistance exercise first, and with a days break in-between.
If you have the time and inclination, it’s also worth doing a weekly session of longer duration moderate-intensity exercise for 30 minutes to a a few hours. A nice hike would be a good example, but you may need to work up to that.
What if I have to take a break?
If injury, illness, or other circumstances stop you doing your HIIT sessions for more than a few days, don’t start where you left off. Instead, take a step or more back to give your body the chance to build up again gradually.
If you want to get benefits like greater cardiorespiratory fitness, body fat reduction, improved glucose control and blood pressure from HIIT, then:
Do 2-3 evenly spaced sessions per week.
Base your intensity on the Rating of Perceived Exertion Scale.
Start with a warmup and then 10 minutes worth of high-intensity intervals, lasting 1-2 minutes. E.g. 10 x 1 minute intervals or 5 x 2 minute intervals.
Your recovery period can be based on a specific time, score, or heart rate range, but the goal is always to allow you to do a similar amount of work in each interval without a major drop off from first to last.
Ensure you keep making progress by building up the total interval time from 10 to 20 minutes, and cutting back on recovery time. Do this slowly, only making adjustments every 3-6 sessions, and then keeping those adjustments small, e.g. adding 10 seconds to each interval, or taking 5 seconds off recovery.
Finally, check with your doctor before starting a HIIT programme.
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1. Hallsworth, K. et al. Modified high-intensity interval training reduces liver fat and improves cardiac function in non-alcoholic fatty liver disease: A randomised controlled trial. Clin Sci (2015). doi:10.1042/CS20150308
2. Laurent, C. M. et al. A Practical Approach to Monitoring Recovery: Development of a Perceived Recovery Status Scale. J Strength Cond Res (2010). doi:10.1519/JSC.0b013e3181c69ec6
3. Borg, G. A. Psychophysical bases of perceived exertion. Med Sci Sports Exerc 14, 377–381 (1982).
4. Navalta, J. W., Tibana, R. A., Fedor, E. A., Vieira, A. & Prestes, J. Three consecutive days of interval runs to exhaustion affects lymphocyte subset apoptosis and migration. Biomed Res Int 2014, 694801 (2014).