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Short sharp sprints of intense exercise are becoming an increasingly popular way to get a fast fitness fix. But as Bryce Hastings, Les Mills Head of Research, explains relying on quick workouts alone might not be the smartest move.

You know you’re getting old when you begin statements with: “I remember when…”

Well, guess what? I remember when we were all obsessed with low-intensity, long-duration workouts because they got us into the ‘fat burning’ zone. Gyms everywhere were full of people walking slowly on a treadmill while reading a magazine. Heaven forbid you broke into a jog – then you’d be burning carbs!

The theory seemed good. We burn mostly fat during low-intensity activities (you’re probably burning mostly fat while you’re reading this). The problem is you don’t actually burn much of anything – because the intensity is so low.

As a response to the lack of effectiveness from exercise at a sleepwalking pace, high-intensity workouts appeared. No more reading magazines … Have you ever tried to read a magazine while you’re doing a burpee with a tuck jump? Suddenly, fitness gurus everywhere were competing to see who had the toughest workout.

Fast forward another few years, and now we have what researchers are terming ‘sprint intervals’ – short bursts of very high intensity with the claim that even four-minute sessions can change your life. In fact, the latest idea is that intervals just four seconds long are enough to change your fitness and muscular output!

The tendency when something new and sparkly comes along is to throw out the old approach – because it’s just old, and newer must be better. However, as my good friend Dr. Jinger Gottschall says: “We have decades of research demonstrating the effectiveness of longer duration workouts – why would we suddenly think they have no benefit?”

So where does this leave us? Should we go with four-second sprint intervals or the more traditional longer sessions?

Well, luckily, we have research that might help. Canadian researchers compared sprint interval workouts to endurance sessions over a period of six weeks in a group of overweight / obese males. Twenty-three participants were randomly assigned to one of two groups. The sprint group did four to six intervals of 30 seconds duration at maximum intensity on a stationary bike with two minutes recovery between each set. They performed this exercise session three times per week. The endurance group did five biking sessions per week of 30 – 40 mins duration, each at 60 percent of their maximum intensity.

What I found most interesting about the findings of this study was that both approaches generated positive benefits, but the benefits differed between the two groups. Both increased fitness and glucose tolerance. Only the endurance approach, however, decreased blood pressure, abdominal fat and something called ‘post prandial lipid tolerance’ (the amount of blood fat that accumulates after a meal). Also (and this is important) the observed improvements in glucose tolerance were better on the days either group exercised.

So, what does all this mean?

If you like the idea of short sharp workouts and exercising at an intensity that can be compared to being chased by a bear, sprint intervals are great. If you’re happy to do longer sessions with less intensity, endurance sessions are also great. But really a combination of sprint intervals and endurance sessions is best.

Research from our lab used LES MILLS GRIT to demonstrate the superior effects of a combined approach. Active adults who combined four moderate to vigorous workouts with two 30-minute high-intensity LES MILLS GRIT workouts each week, showed significant improvements in nearly all the variables we measured. These improvements in VO2, triglyceride levels, strength and a series of other benefits, happened in a mere six weeks! Plus, participants expressed their delight in the training variety and had really high levels of overall satisfaction with the experience!

We cannot discount the effect of frequency. Training most days, whether it's high intensity or endurance, means you are moving more often and off-setting the effects of being sedentary. This was evidenced in the Canadian study by the fact that the participants had better control of their glucose on the days they trained – regardless of what type of session it was.

One of the criticisms of doing nothing but sprint intervals is that you can’t do the workouts too often. Research shows that too much high-intensity interval training can result in negative effects. And in the Canadian study sprint participants exercised just three times per week compared to five for the endurance group. Even the four-second group could only train three times per week. A mix of workout intensities allows you to do your endurance training on the days you’re not doing the sprint intervals.

So, in summary – try to be active most days. Embrace training in sprint intervals a couple of times a week to give your fitness a nudge. And don’t let endurance training become an “I remember when…” thing of the past. Endurance workouts may be too slow to outrun that pesky grizzly, but this more chill type of exercise means you can come back and train tomorrow as well.