When you first start working out, your body will go through a number of changes. These changes are designed to provide you with more energy and your ability to recruit that energy as and when you need it, is one of the biggest factors in determining how fit you are and how well you’re able to train. It’s also what controls the amount of fat you’re able to lose in any given amount of time!
Let’s see how this works and what you can do to improve it…
The ATP-CP System
Essentially, the body finds its energy using three separate systems and it goes through these three systems in order.
When you first start exercising, you will begin using what is known as the ‘ATP-CP’ system. This stands for adenosine triphosphate creatine phosphate system. Catchy!
Adenosine triphosphate is the most fundamental form of energy known to biology. This is what glucose must be broken down into in order to be used by the body and a fair amount of it exists inside your muscles at all times. As soon as you start exercising, you utilize that ATP and this provides up to a couple of seconds of power. CP – creatine phosphate – allows us to recycle ATP and is also stored in the muscles ready to use.
The ATP-CP system is the most energy efficient and provides us with energy without making us gasp or feel unwell.
The Glycogen Lactic Acid System
The glycogen lactic acid system works by using glycogen stored in the muscles. This is the second most energy efficient source but has the unwanted side effect of producing lactate and other metabolites as a by-product. Lactate makes us feel unwell if we keep pushing ourselves and correlates with other metabolites that can make the muscle feel like it’s burning.
We can usually use this system of energy for a couple of minutes before the lactate becomes too much or the burn becomes too much. It is possible to improve your tolerance to this however, with training.
The Aerobic System
Finally, we switch to the aerobic system. This is the energy system most of us are most familiar with and it works by utilizing oxygen in the blood in order to burn fat stores for energy. This is why it makes us start breathing more heavily and increases our heart rate.
The aerobic system is the least energy efficient and it takes time for the energy to be delivered. Thus we are forced to slow down once we reach this state. However, it is also the type of energy system that we are able to sustain the longest. In fact, we can continue with this kind of exercise indefinitely or until we collapse from a complete lack of body fat!
HIIT
HIIT (high intensity interval training) is so effective because it involves switching from the first two types of energy (anaerobic energy) to the last kind. This enables you to deplete both your glycogen and your fat stores and thus does both more effectively.
If you’ve read just about any fitness blog, magazine or website in recent years, then you’ll likely have come across HIIT.
HIIT: high intensity interval training. Sprinting at maximum heartrate for a short period of time and then switching to a slower form of exercise for a couple of minutes to recover before starting the whole cycle again.
This type of training is all the rage because it is known to burn more calories in less time when compared with steady state cardio. And it’s great for our VO2 max, mitochondrial function and more.
But why? How does it work? What makes it so special?
What Happens When You Push it Hard
When you engage in HIIT, you start out by pushing hard and going at or near to your maximum heart rate. This is what makes all the difference, as now you are depleting your body of all of its readily available energy in order to drive those fast twitch muscle fibers. This is anaerobic training and it relies on ATP stored in the muscles, as well as glycogen.
After this, you then switch to your regular exercise at around 70% of your maximum heart rate. This is a steady pace that you can maintain, that burns fat using the aerobic system and that allows you to recover and reduce the lactate and other metabolites that build up in your blood during intensive exercise.
Welcome to After Burn
Steady state cardio is normally something you can maintain for a long time before you start to tire out and this is why a lot of people will exercise by running at a steady pace for 40-60 minutes.
If you do this after having done high intensity training however, you will be running at a point when you have very little available energy in your muscles and in your blood. All the glycogen has been used up and thus you have to rely even more on fat in order to keep going. Your body becomes more efficient at burning fat and you see greater benefits from the short amount of training that comes after.
But this isn’t even the best bit. What’s so good about HIIT is that this after burn effect continues for hours after you finish training. You’re now going about your usual activities with less glycogen, which means you’ll burn more fat even to do regular things like picking up a fork, or walking across the room!
