By Gavin Gillibrand

Having recently ran both a straight 5km and a HIIT (high intensity interval training) 5km on a treadmill, I thought I would explain the difference between the two in terms of calories burnt and fat loss.

Which of the two is more beneficial and why should you prefer one over the other?

A few weeks ago, I ran a steady 5km in 24.41 min. Nice and steady, working reasonably hard but not pushing myself too much. Estimated calories burnt was 423. Remember, unless you programme your weight, height, body fat and various other measurements, the treadmill can only guess this so don’t pay too much attention to this.This week I ran a 5km HIIT in 28.56 mins. Considerably slower and calories burnt was 356.

On the surface, it would appear that the straight 5km was much more beneficial all round but lets look closer to see if this is the truth.The average speed for the straight 5km was about 12kph compared to just about 9kph for the HIIT 5km. Compare the calories and you can see the straight 5km beats the 5km interval run by 67 calories and it was performed 4min quicker. The straight 5km is looking like the winner here….until we compare the average heart rate and the amazing properties of a little known phenomena called EPOC. More on that in a minute.

First, lets look at the heart rate and why that is important. I wore a heart rate monitor for both runs and my average heart rate for the straight 5km was 149 bpm. It pretty much stayed the same rate the whole run as I kept the same speed on the treadmill. The HIIT 5km involved me taking the speed up to 18kph for up to 60 secs at a time during a sprint phase and then back down to 6kph for 60 secs. During the sprint phase my heart rate hit 183bpm and even on the 60 sec walk at 6kmp it never dropped much below 145bpm. Average heart rate was about 161bpm for the total session. This means that over the whole 29mins of the HIIT 5km, my heart was working on average 22bpm more than during the straight 5km. Interesting.

Was does this mean in terms of fat loss?

Well, lets look at the calories to start with. Apparently, more calories were burnt in the straight 5km but this is where the HIIT session become so valuable. With the steady 5km, calories will cease to be burnt as soon as the activity is over. The metabolism will return to its normal rate and the workout will no longer produce results in terms of calories burnt. Although fewer calories were burnt during the HIIT session, the metabolic rate of an individual will be raised for 24-36 hrs after the activity through a process called EPOC or the “afterburn” as its more commonly known as. EPOC is an acronym for Excess Post-exercise Oxygen Consumption. I couldn’t put a figure on the number of calories burnt but that is largely irrelevant as in terms of fat loss, the HIIT is just way more effective.

Lets go back to the heart rate. We know that my heart rate was working on average 22bpm more and for 4 mins longer. What this means is that my body was actually working harder even though the workout took longer to complete. It didn’t matter to my body that it took 4mins to complete the same 5km, it will only understand that the output of my heart was higher which means the metabolic demand placed on my system would be far greater.

There is a place for a steady 5km run. If you like running and want to keep fit and healthy then by all means, run your straight 5km. But, if like most gym members you want the added benefit of burning lots of fat as well as staying fit and healthy, it might be wise to mix your training sessions up and alternate between the steady 5km and the HIIT 5km.I have actually found that by performing the HIIT 5km regularly, it has improved my ability to work harder on the steady 5km as my Vo2 max had increased. Vo2 max is the maximum capacity of an individual’s body to transport and use oxygen during exercise.

After reading this, I hope to see many more people sprinting on the treadmill rather than doing steady rate cardio. If you want effective fat loss that is….

Gavin Gillibrand BSc. Fat loss and Body Transformation Expert in the City of London, UK. Please visit our website http://ultimatecityfitness.com for more great articles like this and how to burn fat effectively