Research Reviews

Research Review: Interval training & type 2 diabetes

by Helen Kollias

A total of 2 hours of high intensity interval training (HIIT) over 2 weeks improved insulin sensitivity in sedentary overweight men and women. HIIT offers exciting possibilities for time-efficient and physiologically effective exercise.

Time seems short in our modern, fast-paced society. We’re all busy people, running from appointment to appointment, working longer, staying up later, trying to cram in more things into what seem like fewer hours.

And what’s often the first thing to go when we’re rushed? Exercise, of course.

Well, here’s some good news: To get and stay fit, lean, and healthy, you might need less exercise time than you think. (For more on this, check out JB’s experiments with exercise minimalism.)

It might sound too good to be true, but recent research shows that only 1 hour a week of exercise for 2 weeks is enough to see improvements.  The key is exercise intensity. If you don’t exercise that much, when you do exercise, you’ve got to make it count.

High intensity interval training (HIIT)

An example of “quick exercise that counts” is high intensity interval training, or HIIT. HIIT is a mode of exercise that alternates short periods of very intense exertion with periods of low intensity — for instance, alternating all-out 10-20 second sprints with 30-60 seconds of moderate walking; or trying to zip up a hill on your bike alternated with slow leisurely coasting.

In fact, the cool thing about HIIT is that there are endless possibilities for things you can do. Pick an activity that gets your heart going, and do it with as much all-out effort as you can muster. Then take a break and cruise. Heck, even housework can be HIIT if you do it right.

Because the effort for the high intensity period is so high, you can really only do it for 10-30 seconds. And an ideal session of HIIT is usually somewhere between 5-15 minutes (excluding warmup and cooldown). If you can do more, you’re probably not getting that high intensity high enough.

HIIT with the same amount of work is as good — if not better than — moderate steady exercise. The problem is that if you factor in the warmup and cooldown time, you often end up spending the same amount of time as the usual “30 minutes of ‘cardio'”.

So what’s the ideal choice for the time-crunched? For the answers on this, I turned to one of the leading HIIT researchers, Dr. Martin Gibala.  Since 2005, Dr Gibala has been studying HIIT, trying to figure out how little time is needed to make a difference.

HIIT: Even a little does a lot

Dr Gibala is particularly interested in low-volume HIIT — how little HIIT can one do and still see benefits? After all, wouldn’t it be nice to spend minimal time on exercise and yet get a pretty good result?

Well, time-starved folks, you’re in luck: According to Dr Gibala, his biggest surprise in researching HIIT is how little volume it takes to get a response.

Supra-max HIIT

Researchers start with what I call supra-max HIIT. You go all out for 30 seconds, take a 4.5 minute rest, then go again for 4-6 total sprints.

Doesn’t sound too bad… until you actually do it. Many trainers love to talk about how their amazing program makes clients puke. Well, this type of HIIT can make you puke. No fancy program needed.

Researchers picked this type of exercise because they use it all the time for figuring out people’s ability to exercise without oxygen. It’s call the Wingate test and doing it more than once in the same day takes a lot of motivation and mental strength. It’s extremely demanding.

On the plus side, supra-max HIIT does work as well as endurance exercise with 90% less volume and 67% less time. Table 1 below compares the two protocols.

Table 1 – Summary of the original low-volume HIIT protocol and endurance exercise used by Dr Gibala’s lab (8)

Variable Supra-max HIIT (original) Endurance exercise
Protocol
  • 30s x 4-6 repeats
  • 4.5 min rest
  • 3 times/week
  • 40-60 minutes
  • 5 times/week
Training intensity
  • All out
  • About 500 W
  • 65% O2peak
  • About 150 W
Weekly training time
  • 10 min exercise
  • 1.5 hours including rest
  • 4.5 hours
Weekly training volume
  • 225 kJ
  • 2250 kJ

So the original HIIT protocol is definitely time-efficient.

Since the original supra-max HIIT is so hard, researchers eventually modified it to be less intense, with a little more time. Instead of 30 seconds all out with 4.5 minutes rest, it’s now 60 seconds at 90% max heart rate (about 150W) with 60 seconds rest, with 10 bouts total.

If you want to read more about HIIT take a look at Ryan Andrew’s All About HIIT article.

gibala sprint training Research Review: Interval training & type 2 diabetes
Dr. Martin Gibala, demonstrating his HIIT form

HIIT and glucose control

OK, so HIIT can be more “efficient”… but what does that really mean? In this week’s review, I look at one measure of exercise improvement: better glucose control. This is particularly effective for folks who are either Type 2 diabetic or well on their way (e.g. people with a lot of bodyfat and poor diets).

For this week’s review I look at one of Dr Gibala’s recent publications:

Little JP, Gillen JB, Percival ME, Safdar A, Tarnopolsky MA, Punthakee Z, Jung ME, Gibala MJ. Low-volume high-intensity interval training reduces hyperglycemia and increases muscle mitochondrial capacity in patients with type 2 diabetes. J Appl Physiol. 2011 Dec;111(6):1554-60.

Methods

Most HIIT studies use healthy, relatively lean university students. That’s helpful if you want to study, say, college athletes. But it’s not as useful if you want to know about applicability to a more “average”, older population who might be overweight and more sedentary — and who might need the health benefits of exercise the most.

So, one thing that makes this study unique was that researchers used Type 2 diabetics who were obese (average BMI of 32 kg/m­2 ), and on average, 61 years old.

Pre-HIIT Measures and Tests

Everybody had their waist girth, height, weight, resting heart rate and blood pressure measured. They also were hooked up to a 12 lead ECG (electrocardiograph) before and after having their ability to use oxygen (VO2peak) tested on a bike (ergometer).

Researchers tested how much oxygen the participants could use so that they could calculate the appropriate intensity for the upcoming intervals. Based on the results of the VO2peak test the researchers knew the peak power during the test (measured, by the way, in watts — just like your light bulb).  All sprint intervals of the HIIT sessions were about 90% of participants’ max heart rate, based on this oxygen test.

Continuous glucose monitoring and muscle samples from the outer mid thigh (lateral region of the vastus lateralis) were done before and after training. Although this part of the thigh doesn’t seem to be particularly involved in cycling, researchers choose this site for the muscle biopsy in order to avoid major nerves and blood vessels while getting at least some idea what’s going on during cycling.

Does it hurt? Yes and no. There is a local anesthetic used on the skin, but no anesthetic in the muscle, where you feel mostly pressure. If you relax, then the whole thing feels weird, but not what I would call painful.

Back during my master’s I had 10 pieces of hamburger taken from my legs in total. It’s not as bad as it sounds. (If you’re considering doing graduate work in exercise physiology, consider yourselves warned. You’ll probably be donating muscle at some point for some prof’s study.)

Exercise training

For 2 weeks the volunteers did HIIT on Monday, Wednesday and Friday. Each HIIT session involved the following:

  • 3 minutes of warm up (at 30 watts)
  • 10 sprints lasting 60 seconds, alternated with 60s of recovery
  • 2 minutes of cool down at 50 watts

Total time per workout session: 25 minutes, with 20 of those spent doing the HIIT protocol.

Figure 1 is a graph of what it the workout would look like if it was a program on one of those fancy workout bikes.

HIIT protocol bar chart 1024x520 Research Review: Interval training & type 2 diabetes
Figure 1 – HIIT session breakdown

Results­

Average blood glucose levels over 24 hours improved after training. This means that after training for only 2 weeks, participants already had better blood glucose control. Better glucose control means better metabolic health for type 2 diabetics.

Another bonus for volunteers was that HIIT increased mitochondrial capacity.

Mitochondria are the “energy factories” of our cells, so by increasing their number and output we can increase our ability to produce energy effectively. This is particularly important as we get older, as mitochondrial function goes down with age.

Discussion

Here are some of the key take-home points from the study.

HIIT’s benefits are quick.

Only 2 weeks of 60 minutes of intense exercise per week quickly improved two important physiological indicators.

In this study Dr Gibala’s big finding wasn’t that you could improve endurance or lose weight, but with only 6 HIIT workouts and a total of 2 hours of time volunteers had improved glucose handling, a key issue with type 2 diabetics.

Only 2 hours! I’ve spent 2 hours waiting in a doctor’s office and that was all in the same day.

HIIT’s benefits apply to nearly everyone.

You could argue that in this study the volunteers were older, overweight, and diabetic, so no wonder they improved. I’d agree, but Dr Gibala did a similar study using the same HIIT workout program with healthy young men who were active (8). In that study, the volunteers had improved cycling times.

Other studies have found that HIIT is also great for losing fat.

You need to keep the H in HIIT.

In order to make the magic, the high intensity has to be high. Doing HIIT with not enough intensity will not work.

HIIT can accommodate a variety of people.

Think HIIT is too much for you? Probably not.

How well do older, possibly overweight populations with cardiometabolic diseases such as Type 2 diabetes handle the high intensity of HIIT?

“Very well,” says Dr Gibala, “and to date we’ve haven’t had a single drop out.” Participants seem to enjoy HIIT more than moderate exercise, and improve quickly. There’s no need to throw out traditional steady-state cardio, he says, but this is an appealing alternative.

Bottom line

A total of 2 hours of high intensity interval training over 2 weeks improved insulin sensitivity in sedentary overweight men and women. HIIT offers exciting possibilities for time-efficient and physiologically effective exercise.

References

Click here to view the information sources referenced in this article.

Learn more

To learn more about making important improvements to your nutrition and exercise program, check out the following 5-day video courses.

They’re probably better than 90% of the seminars we’ve ever attended on the subjects of exercise and nutrition (and probably better than a few we’ve given ourselves, too).

The best part? They’re totally free.To check out the free courses, just click one of the links below.