HIIT: How exercising for just a few minutes can keep you healthy and fit
- Gavin
- Jul 30, 2021
- 7 min read
Updated: Aug 4, 2021
Hi friends! I hope you’re all having a good summer, and keeping well. Today, I want to speak about the amazing benefits of High Intensity Interval Training, or HIIT.
Summary: Just a few minutes of total exercise, when done in short, intense, bursts can yield similar – and potentially even greater – benefits, compared to much longer periods of ‘cardio.’
Full post:
As I touched on before in my post on the importance of maintaining stable blood sugar levels, exercise is perhaps the single best thing you can do to stay energetic, healthy, and youthful, even as you age chronologically. But, are all forms of exercise equally beneficial? And, what if you struggle to find the time to maintain a consistent exercise regimen?
Decades of research provides a provocative answer to both these questions. It turns out that one particular form of exercise, which has become known as High Intensity Interval Training (HIIT), can provide outsized benefits, in a fraction of the time that other forms of exercise require.
What is HIIT?
HIIT refers to a mode of exercising whereby you exert yourself at a very high level, for brief periods of time, and rest in between. This can involve various forms of movement, such as running, biking, swimming, floor exercises (e.g., burpees, pushups) and movement with weights (e.g., kettlebell swings). The most common forms tend to involve traditional ‘cardio’ movements. For example, on an exercise bike, you could:
1) Alternate 30 second periods of high effort (fast and with the resistance up), with 30 second periods of low effort (slower, with low resistance), for five minutes total.
2) Rest for two minutes, and then do one more five minute session.
3) Your total workout time is 12 minutes! Assuming some warmup and cool down, maybe 15-20 minutes.
There are various other forms of HIIT that differ slightly from one another. Ultimately, the important thing is to do short bursts of high-intensity activity; the exact protocol that you use is less important. For simplicity sake, I would suggest starting with the basic 30/30 protocol described above. Depending upon the exercise you are doing – and whether you are completely resting versus just going ‘slow’ – you could shorten the rest period. Or, if you are just starting out, I would suggest using longer rest periods (and perhaps also shorter exertion periods) and progressively shortening them as you gain fitness.
Here are a couple of other HIIT protocols:
1) 'Tabata’ training has become quite popular, and involves the following schedule:
- Do an exericse at high intensity for 20 seconds
- Rest for 10 seconds
- Complete 8 rounds
- Rest for one minute
You could do this for say four different exercises (e.g., pushups, exercise bike, burpees, kettlebell swings), for a total of a 20 minute workout. Here is a highly rated app that can guide your tabata workouts; I have not tried it myself yet. https://apps.apple.com/us/app/tabata-pro-tabata-timer/id346432063
2) Another form involves going all-out for 30 seconds, followed by 90-180 seconds of rest, and repeating several times. The advantage to this technique is that you should be close to fully rested after those 90-180 seconds, so you can maintain your maximum intensity during the intervals. Indeed, some recent research suggested that just 6-9 minutes of total exercise per week, if done in increments of 20 seconds of all out effort, with rest periods of four minutes in between, is as effective as five hours of continuous exercise.
3) And yet another form involves intervals of 4 minutes of high exertion – obviously at somewhat lower intensity than with 20 or 30 seconds periods of exertion – interspersed with 3 minute periods of light exertion.
And, many personal trainers and fitness classes incorporate elements of HIIT, such as in Spin, Peloton, and Crossfit workouts.
Benefits of HIIT
So, why do HIIT? A wide range of research points to the health benefits of short periods of intense exercise, as captured in several recent meta-analyses (these are papers that aggregate across many studies that have examined the same or similar research questions). These meta-analyses consistently show that HIIT training (over periods ranging from four to twelve weeks) causes greater improvements in cardiovascular fitness than does longer periods of moderate-intensity continuous training:
For example, the first of these aggregated across 28 studies of healthy adults aged 18-45, and found that although both HIIT and continuous training led to improvements in VO2max (a common measure of cardiovascular fitness), this increase was even greater amongst those in the HIIT condition.
Another meta-analysis found that HIIT training caused greater improvements in blood sugar and insulin resistance than continuous exercise, suggesting that HIIT training may be more effective than more standard 'cardio' at preventing diabetes.
And, one study examined long-term outcomes in the form or mortality amongst over 1500 people in their 70s in Norway. Amazingly, they were able to get participants to stick to their randomly assigned exercise regimens for five years, which included either 1) twice weekly periods of 50 minutes of steady state exercise, or 2) twice weekly HIIT sessions. Participants in the HIIT condition were 3% less likely to pass away during the study period.
Why does HIIT work?
At this point, you might be wondering: why does HIIT have all these benefits? The answers are complex, and still being investigated, but briefly, they seem to include the following:
- High intensity exercise may boost metabolism and improve blood glucose for a significant period of time after the workout is complete. In other words, the effects of a HIIT workout are not only felt during the workout, but for a substantial time afterwards. This is why tracking calories burned during a workout doesn’t make sense, because your metabolism may stay elevated for many hours after the workout, leading you to continue burning calories at an increased rate (and this appears to happen more for HIIT workouts than continuous exertion). For example, this study found that a single HIIT session led to improved blood sugar levels 24 hours after the workout.
- HIIT training may lead to improvements in mitochondrial health (e.g., density and size of mitochondria, the ‘powerhouse’ or energy production center, of our cells)
- HIIT training may lead to hormonal improvements, such as heightened testosterone and growth hormone, which decline with age.
Are there any downsides to HIIT?
Of course, it is important to consider any possible drawbacks to HIIT. First of all, HIIT doesn’t always outperform continuous exercise, on every metric. The evidence on weight loss is mixed, with one meta-analysis cited above finding that HIIT causes greater weight loss than continuous exercise, but another finding the opposite (in my opinion, this is likely due to differences in the exact HIIT protocols used). However, given how much more time-efficient HIIT is – typically taking about 30-50% of the time of continuous exercise, even accounting for rest periods – I personally think that it’s still a better option.
Second, HIIT may be difficult for those who are relatively unfit or have been sedentary for a period of time. In such cases, I recommend ramping up slowly – research shows that even substantially easier HIIT protocols can still be beneficial. Ultimately what matters is that you feel substantial exertion during the ‘on’ periods, and that you rest long enough in between them to allow yourself to maintain that intensity across several intervals.
Third, HIIT training can sometimes pose greater injury risk. Crossfit, for example, sometimes involve doing heavy lifts ‘for time’ (i.e., as fast as you can). This can be an amazing form of exercise, provided you are able to maintain the correct form and have the range of motion needed to conduct these exercises safely. Otherwise, risk of injury can increase. Similarly, if you have not sprinted in years, you should work up to full-speed sprints slowly, lest you pull a hamstring. If you do work up slowly and avoid heavy weights with HIIT, you will minimize your risk of injury.
Finally, I don’t recommend that you do HIIT all the time. It is, by definition, high intensity, and your body needs some time to recover. 2-3 times per week is sufficient; more may be detrimental. Also, there may be some benefits to occasional lower intensity, but much longer, periods of exercise, such as a vigorous hike or a long run.
My personal HIIT protocols
Just in case it’s helpful for giving you ideas about how to incorporate HIIT into your regimen, here are the ways in which I use it:
- I personally love sprint training. There’s something amazing about running as fast as you can (provided you can do so without pain; again, this is something you must work up to). So, about once a week, I’ll do a series of 100m sprints at the track, with 90 second rests in between. I do like the track for this because it is a softer, more forgiving surface than a road.
- I also incorporate intervals into longer runs. This could be at the track, where, for example, I might run two miles alternating 30 seconds at about 75% top speed, with 30 second at about 35% top speed. During the winter, I sometimes do this on a treadmill, switching back and forth between 11 mph and 5 mph. Or, if I go for a run around the city or along the river, I’ll mix in occasional 30 seconds fast bursts.
- The kettlebell swing is an amazing full body workout in a single exercise, combining resistance and cardio training. I sometimes do 4-5 sets of these, with 30-60 second rest periods in between.
- When I’m traveling and staying at hotels – or dealing with an injury that prevents me from running – I’ll do 20/15 workouts on an exercise bike, for 3-4 minutes total, 2-3 times, with 2-3 minutes rest in between each ‘set.’ Or, I’ll do intervals in the pool, where I swim 4 laps fast, rest for 1-2 minutes, and repeat several times.
- Once in a great while, I'll use the stairs in my apartment building - stairs work great for HIIT! I'll run up like 5 flights and then go back down, and repeat several times.
Summary
In sum, HIIT is an amazing way to increase/maintain your health and fitness, in a very time-efficient manner. Furthermore, people often report that HIIT is more enjoyable than long periods of steady state exercise. If you are not incorporating into your regimen, I strongly suggest that you try it!
To your health,
Gavin
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