I know what you’re thinking. I can read your mind.

“Not another article espousing the benefits of high intensity intervals.”

If you read our content you know we like short, intense workouts. We wrote about the benefits of working out for just 13 minutes in late 2018. One of our favorite researchers, Marty Gibala from McMaster, wrote a book literally called ‘the one minute workout’. We even wrote a blog last month about our 3 favorite high intensity interval workouts! 

Yet we recently realized we have failed to answer the single most common question we get about interval training……is interval training actually better then slow, continuous, long cardio sessions for burning fat?

Lucky for us that very question was tackled by the British Journal of Sports Medicine (BJSM) in February.

Now it’s easy for fans of either camp to ‘cherry pick’ studies proving why their method is best. This BJSM article is something called a meta-analysis that essentially groups all of the data from similar individual studies to draw more definitive conclusions.

We recognize that everyone wants to burn fat. But there is one BIG issue. Typical physical activity guidelines recommend 150-250 minutes/week and up to 60 minutes/day of moderate intensity aerobic exercise to prevent weight gain. To lose considerable amounts of weight, some suggest at least 420 minutes/week. Who has time for that?

Enter interval training. Really there are 2 types:

• High Intensity Interval Training (HIIT): near max effort at a heart rate over about 80% of your maximum (think middle distance sprints)
• Sprint Interval Training (SIT) – all out effort for very short duration.

Both are interspersed with recovery periods that are either active (like walking) or passive (like splaying out on the ground because you feel like you’re dying).

In the studies included in this paper, interval training was compared to Moderate Intensity Continuous Training (MOD), which is continuous effort at 55-70% of your max heart rate (think a long leisurely jog with a friend).

The great thing about this meta-analysis was the variety in exercise types used in the individual studies that it drew data from. In this case, there were a total of 41 studies of which 20 used cycling, 16 used walk/jog/run, 1 used an arm ergometer, 1 used swimming, 1 used boxing, 1 used a rower, and 1 provided a choice. All of them compared intervals with MOD. This is great as it immediately makes it way more applicable to a large audience of fitness enthusiasts. How broad? The included folks were aged 10 all the way to 70! (The studies on 10 year olds were on obese children….an increasingly problematic public health issue).

So what was found?

Essentially there were 3 main conclusions:

• There was no superiority of interval training or MOD in the reduction of total body fat percentage
• Interval training was superior in the reduction of absolute total fat mass
• Sprint interval training was best for absolute fat mass loss

Why does SIT burn the most fat? Have you ever tried a sprint workout and then can’t stop sweating for an hour or two after? When you work at your absolute hardest effort, you end up persisting in a state called postexercise fatty oxidation that seems to be associated with burning more fat. So your workout may be shorter but but your furnace burns much longer.

To understand the above conclusions better, here is a neat comparison of the averages for all the protocols in the studies:

• MOD Protocols – averaged 38 minutes for 35 sessions (1330 minutes total) and saw a reduction of 3.5% total body fat%
• HIIT had an average of 28 minutes for 33 sessions (924 minutes total) and provided a reduction of 4.6% total body fat%
• SIT lasted just 18 minutes for 29 sessions (526 minutes) and had a reduction of 3.5% total body fat.

That sparked our interest. SIT burned the exact same total amount of body fat yet you worked out less then 40% of the total time!

If you are a fan of efficiency, the variables that increased fat loss even more within the HIIT and SIT workouts included being coached or supervised (turns out some folks don’t push themselves hard enough on their own) and using a run/walk program as your primary form of exercise.

There you have it. Work out harder…..not longer. Mix in some sprint, all out effort workouts. You will burn more absolute fat, save yourself a ton of time, and believe it or not your performance will improve. See you at the track!