Energy Systems can be a really complex topic, or a really simple one. As I don’t expect any of you looking for information to write a scientific paper here, I’m going to make it as simple as possible.

In short, we have different energy systems that we use for different activities. Some use creatine for fuel, some carbohydrates (glucose) and some fats (lipids). Depending on what type of activity you focus on, you can choose what type of fuel you use. Although nearly all activities will use a combination of all fuel types, there will definitely be a dominant fuel source.


The Energy Systems

Energy Systems

Our energy systems are broken up into sections depending on how much power an activity requires. As you can see from the image above, the more power required to perform an exercise, the higher the energy burden. Sports such as olympic weight lifting, where an ultra high power output is required, but only for a split second, will rely on the ATP (Adenosine Tri Phosphate) or CP (Creatine Phosphate) energy system for its fuel. Whereas an activity like walking, which requires very little power output, will use fat for fuel.

As the image above shows, very low power output activities, such as walking, leisurely swimming or NEPA activities are best at utilising fat for fuel. However, they are not usually the most efficient. While these activities do mainly use fat for fuel, the amount of fuel required for the activity is minute. You’d have to walk for several hours a day just to see a difference. This is why these activities are great as a supplement to a more demanding exercise routine, but shouldn’t make up the bulk of it.

Most people make the mistake of thinking that traditional cardio, spending an hour on the treadmill or cross trainer will be a lot more efficient at burning fat. But as the image above shows, that falls into the Aerobic Glycolosis energy system, which uses carbohydrates for fuel. So while you are burning calories, very few of them come from fat. All you’re doing is using the glycogen (carbohydrates) stored in your muscles for fuel and then replacing them as soon as you have your next meal. Great for fitness, but not optimal for fat loss.

Enter High Intensity!

A few weeks ago, I gave you a sprinting workout. A workout that’s optimal for fat loss, but you may be looking the image above and thinking that sprinting comes no where near the fat for fuel energy system. And you’d be right. However, sprinting and other ANaerobic activities have a trick up their sleeve; Oxygen Debt. These ultra high power/intensity activities require the body to up it’s oxygen intake so it can adequately recover. Even those these energy systems may only be able to power us for a few short seconds, they require the amount of time to recover. This sounds extremely inefficient, but it’s this inefficiency that becomes our best friend when it comes to losing body fat.

When recovering from high intensity exercise, the body increases it’s oxygen intake to restore the body to it’s pre-exercise state. This increased oxygen consumption helps replenish the ATP and CP energy systems so that you can use them again to perform more high intensity activity. Due to EPOC (Excess Post Exercise Oxygen Consumption), the body requires extra fuel to help the oxygen repair and recover all of the systems that were just used. This is where Fat breakdown comes in. The body will break down fat, to help the body recovery from the high intensity activity and any fat that isn’t used up in the recovery process will go back into storage.

Smarter Workout for More Fat Loss.

Now you know how high intensity workouts can release a lot of fat to use, it’s time to start thinking about what type of workouts you can apply this theory to. We know that ultra high intensity workouts that use the ATP, CP and ANaeobic energy systems require the most recovery, meaning they burn the most fat. We also know that that these energy systems are best utilised by exercises that last between 0.1 and 60 seconds. So what workouts should you chose to make sure you’re within those parameters?

Going to the gym and doing a high intensity class for 15-30 mins is NOT the high intensity we’re looking for. You may feel battered and destroyed. You may feel like you’ve given it everything and worked your heart out. But, you’ve worked out for 15-30 mins straight, with very little rest. Guess what?! You’re using the wrong energy system for fat loss. You may have burned a bunch of calories, but hardly any have come from fat.


A Better Way…

Workouts that create the highest oxygen debt, may be the ones where you feel like you’re not burning much fat, but will actually require more fat burning to facilitate recovery. Very short activities, such as Olympic Lifting, Strength training, resistance training and power based workouts, only have you working for 1-60 seconds at a time, but will create the most after-burn or oxygen debt. Even sports like tennis or squash where each point lasts between 20-45 seconds and requires a lot of intensity will create a great oxygen debt. They will release the most fat to aide recovery while also allowing you to become stronger and fitter.

However, you have to remember that any fat that isn’t used up in the recovery and restoration process of the ATP and CP energy systems, will be sent back to storage, which we don’t want. So think about adding 15-30 minutes of walking at a slight incline and a reasonably pace at the end of your workouts. This will ensure that any fat floating around is used up and very little, if any at is sent back to storage.