High Intensity Interval Training
The idea that we can train for a very short time, albeit very hard, and get all the same benefits from a long (slow) run is obviously appealing to many people. So it’s no surprise that there’s a model or theory for how “high intensity interval training” (HIIT, as you may see it written in marketing materials) can transform your running performance, fitness and your time management.
HIIT became one of the hotter topics in sports science about a decade ago, not only for potential performance benefits, but because it was found to improve fitness and health elements in ways similar to “normal training”. The early studies compared HIIT to normal, long-duration endurance training, and it stacked up pretty well – the same blood sugar, fat-burning benefits that you get from that 45 min steady exercise session were found to have occurred after a session that lasts only 20 minutes!
Too good to be true? Perhaps, but there are some key principles that you can apply and get the best parts of HIIT without the downsides. Let’s first understand exactly what HIIT involves.
To start, the concept of ‘interval training’ is that instead of doing say 30 minutes of continuous exercise, you slice those 30 min up into shorter periods where you might run a little faster than usual, and other periods where you walk or run slower than usual. You repeat this on-off pattern for 30 minutes, and that’s your training session. For instance, you might run faster for 3 minutes, then walk for 2 minutes, repeated six times.
The idea is that the walk provides the recovery that enables you to run faster. And running faster is beneficial because it creates metabolic, neural and cardiovascular challenges that make for better runners. Plus, interval training can be fun – it allows you to express a different side of yourself as a runner. To feel fast. The wind in your hair, a feeling of power. And remember, fast is relative, so anyone can experience those feelings!
The thing about HIIT is that the “on” periods, those slices where you push the pace, are REALLY ON. You go hard. We’re talking close to max. Which is why it’s not always suitable for running – going max as a runner is pretty risky. One famous example of an HIIT session would have you go for 20 seconds flat out (you’re channeling your inner Usain Bolt if you’re running), with a two minute rest, repeated three times. That ENTIRE SESSION will last seven minutes in total, and it became famous when some research studies showed that doing that three times a week produced the same fitness benefits like increases in VO2max that four hours of running in the usual 45 min five times a week did. But because that’s a 20 second period, it has be pretty close to maximum, and this is where the risks come, especially when running.
Another example is a 60 second “on slice”, with a 60 second “off slice” to recover, repeated 10 times. That’s a 20 minute session, and because that on slice is longer, you wouldn’t do this flat out, but it would still be very hard, almost a sprint. This makes HIIT sessions a bit different from a normal running interval session, where you might go 1km fast (taking anything from 3 to 6 min, depending on your speed), with a 3 min recovery, repeated 5 times. For HIIT, there’s no holding back – you’re on the limit, even above it, because it’s so short. The key is that you still have to measure your effort on the hard interval so that you could recover during that 60 second rest period, which may take a bit of practice, but these are hard sessions, very demanding.
Which brings us to the problems. When the scientific studies came out suggesting similar benefits in what could be a shade over 20 min a week, compared to three hours, a lot of people would have thought “This is great, I’ll just do this from now one and save hours”. Problem is, they make a few mistakes. One is that they don’t do the “on” section hard enough. I can’t stress enough how hard it needs to be to trigger the same adaptations. And yes, you could dial it back a little, and make the session feel a bit more pleasant, but then you lose the benefit proportionally – maybe you get only 40% instead of the full effect.
But, if you do hit the intensity, then you have two new challenges. One is that it’s really, really hard. That 10 min session is going to ‘hurt’ much more than the 45 min easy run that you might replace it with. Some runners just don’t fancy that, which is fine. You have to have the right mindset or personality to accept and tolerate the kind of discomfort you’ll feel by the time you’re doing the seventh 20 second flat out sprint, given that you’ll only recover for 2 minutes each time! If you don’t, then rather dial it back and do longer intervals with more control.
And then, there’s the big risk – Injury. This is particularly true for running, which has a high risk of injury to begin with, but which really goes up massively for sprinting. It takes really strong muscles and good co-ordination to sprint effectively and safely, and if you’re not accustomated to this, it really is a shortcut to the physiotherapy rooms. Hamstrings and calf muscles beware!
So if you’re going to do HIIT as a running session, then you really are taking a risk. I’d advise that you use HIIT for cross-training instead, as explained below. But for running, if you are set on it, it would be worth taking the foot off the gas, at least until you learn your limits. Despite what I said above about going hard, if you’re going to try this, give it three to four weeks to get up to speed – first day, think of yourself as a city car, cruising through the gears, and “feel” your range, never getting into even fourth gear. Maybe by week four, you can visualize the McLaren F1 car, but just be careful! Also, once a week is more than enough in terms of keeping that risk down.
It might also be useful to do them on a hill, because that limits your range of motion, which makes them a little safer. But, your best bet Is to use the HIIT concept during a gym session when you can get onto an exercise bike and do them without the impact that running causes. 20 seconds of trying to spin the pedals off the bike each time will be pretty safe, and you can really control this session nicely. The other adaptation of HIIT, by the way, is where you do specific exercises for a period of say 60 seconds, with a short recovery. Lunges, box jumps, star jumps, push-ups, skipping, step ups, and so on.
The point is that it’s high intensity, then recovery, repeated for say 10 to 20 minutes. It’s not really a running session, unless you’re a very confident and competent runner who can handle maximum sprinting (which you’ve got to become comfortable with). What it will do is give your system a real “kick”, in ways that your normal running doesn’t, and that’s what makes it useful, potentially transformational. At the very least, if you find your time severely curtailed, it’s a way to do something challenging in a really quick time. Just exercise caution, and get the good without the bad!