The Fat Series – Fat burning during exercise

There are so many research papers, theories and advice giving experts out there on fat burning. Here’s the thing; every body is different. Literally EVERY physical BODY. So everybody burns fat slightly differently. Especially when it comes to fat burning during exercise. Your body type, predominant muscle fibers and your metabolism will all effect how efficiently you burn fat. And in attempt to help you all, I’ll take you through a variety of ways to do so!

Exercise to burn fat

High intensity interval training versus slow, long, steady state cardio

It has long been said that in order to burn fat you must do long bouts of steady state cardio, hitting what is often referred to as the ‘fat burning’ zone of your heart rate. This catchy phrase, often labelled on treadmills and other gym equipment, is said to be 55-70% of your heart rate max (HRM). At this intensity more fat is burned in relative to glycogen (remember last week, when I said glycogen is the main energy source the body uses), at a ratio of approximately 35% fat to 65% glycogen[1]. The higher the intensity, the lower the ratio. This suggests that slow and steady wins the fat burning race! But you need to look at calories.

Fat burning % and calories

Say, for example, you exercise for 30 minutes at 55% HRM. At that intensity you may burn 200 calories, 35% of which is fat. That’s 70 calories of fat. If you work out at a higher intensity for 30 minutes, at 85% of your HRM, you could burn 400 calories. Although the ratio of energy from fat to glycogen may be around 25:75, the 25% of 400 calories is still more fat burned, at 100 calories.

If that hasn’t convinced you to try a bit of high intensity  interval training (HIIT), then maybe this will.

High intensity interval training and the afterburn effect

Not only do you end up burning more fat during a high intensity workout, but the effects are on going. When working at high intensity our body switches to anaerobic respiration – that is, not using oxygen. This creates an oxygen debt, in what is known as excessive post exercise oxygen consumption (EPOC). The energy required to replenish the oxygen debt continues to be required for up to 8 hours after exercises, meaning we continue to burn calories long after the exercise is over.

Don’t ignore steady state cardio

However, steady state cardio has plenty of benefits. For someone who is doing a lot of HIIT, they may find themselves reaching burn out. It puts the body under a lot of stress to work at such high intensities, and therefore cortisol levels are increased. If you are already in a stressful job/situation, these stress levels may be critical, and cause you to become ill. Steady state cardio allows you to have a bit of a rest, whilst still burning calories. And if you are exercising for endurance, long sessions of a steady state are great for calorie burning! Ever heard of ‘hitting the wall’ in a marathon? This is when your body switches to burning fat for energy (and us women are better at it than men – hooray!). And the more you train for it, the better your body gets at it!

Does muscle burn fat?

And let’s not forget resistance training in all of this. You hear it all the time… muscle burns fat. What people usually mean is, maintaining muscle burns a few more calories than fat. Resistance training, and building muscle, will help to increase your metabolism. But there are so many more reasons to include resistance training in your exercise regime. Increased bone density, reduce high blood pressure and increased good cholesterol are all proven benefits. But in relation to burning fat, one key advantage is increasing insulin sensitivity.

Insulin sensitivity

Insulin sensitivity means we can burn fat (note pre-diabetes is a result of insulin resistance)! This means restoring insulin sensitivity has everything to do with using resistance training as the center point of an exercise plan. And not just any resistance training will do. To develop full insulin sensitivity it requires heavy weights and more focused contractions. A study in the February 2008 issue of Cell Metabolism showed that growth of the faster twitch type IIb muscle fibers has the most benefit in insulin and blood sugar control.

The study showed activation of these fibers positively alters the expression of 800 or so genes responsible for insulin sensitivity. Only heavy and full fatigue resistance training and sprinting activates these fibers, aerobic exercise does not.

Key Take Aways:

  • Every body has different fat burning potential, reacts differently to exercise
  • HIIT is a great way to get a quick workout, with a long calorific afterburn
  • HIIT can cause a high level stress response in the body, so cross training is important
  • Increasing insulin sensitivity will have a advantageous impact on fat burn
  • Resistance training with heavy weights to muscle fatigue and powerful, fast movements such as sprinting will have the biggest impact on insulin sensitivity

So you want to combine all these points into one awesome fat burning workout? Try a plyometric (think power) HIIT circuit.

40 seconds of hard work followed by 20 seconds rest:

Squat Jumps

Push up Jumps

Burpee Bunny Hops

Power Bursts

200m sprint as fast as you can

Rest for 2 minutes, then repeat the circuit 3 more times!

(Want a video of the workout? Comment on my Instagram and your wish is my command!)

Next week is the final instalment in The Fat Series. I will be looking at eating for fat loss, as well as timing and planning your meals around your exercise. Have a great week, and remember to leave any comments or questions that you might want answering below!

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[1] Source: Bryant, Cedric X. 101 Frequently Asked Questions about “Health & Fitness” and “Nutrition & Weight Control“. Sagamore Publishing, 1999.


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