How many times have you been told that if you want to lose weight, you need to perform cardio at a low intensity in order to stay in your fat burning zone? This disinformation regarding fat loss has got to stop. What I am about to explain is not difficult to grasp nor is it cutting edge exercise science either. This information and these methods have been broadly accepted and used by top trainers for a while now, but for some reason have not percolated down to the average Joe who just wants to get in shape. Nowhere is this more evident than in commercial gyms, where you’ll see the same people day in day out aimlessly trudging along on the cardio equipment, as fat as ever.
Serious about fat loss
To understand how to melt fat off your bones as fast as possible, you need to understand the basic physiology of our energy systems. Once you grasp this, you will realise why the best fat loss strategy is NOT low intensity cardio, but rather higher intensity interval training methods.
The boring science stuff
To understand our muscles energy systems, we must understand where that energy comes from. Fuel to produce the body’s energy comes primarily from our fat stores (adipose) and from glucose. Adipose is released from the fat stores into our blood stream as free fatty acids (FFA’s). Glucose is stored in the muscles and liver as glycogen and is released into the blood stream as glucose. Energy is produced via a process called glycolysis. Both FFA’s and glucose pass through something called the Crebs cycle to produce ATP (Adenosine triphosphate), a molecule that is the principal form of energy. It is this ATP energy that is immediately usable by the cells and is the energy that powers the body.
The body’s capacity to store ATP is limited as most food energy is stored as body fat or as glycogen in the muscles and liver. Because ATP storage is limited and can only produce energy for a few seconds it has to be continually synthesized.
There are four systems in the human body that create ATP in different ways. There are two anaerobic systems, the Phosphagen System and the Oxygen Independent Glycolytic System, that do not require oxygen to produce ATP. These two systems are associated with short bursts of energy like sprinting or lifting heavy weights.
The two aerobic systems, the Oxygen Dependent Glycolytic System and the Oxygen Dependent Lipolytic System require oxygen to produce ATP and are associated with longer endurance bouts of energy, like marathon running.
Creatine Phosphate is a high-energy compound found in the muscle cells. It is anaerobic, so does not rely on oxygen to produce ATP. Unfortunately, there is only a small amount of Creatine Phosphate that can be stored in the muscles, so this system can only produce ATP for about 8 seconds of maximal muscle contraction. This system is used mainly for high intensity activities such as the 100m sprint or intensive weight training, such as the Olympic lifts.
Oxygen Independent Glycolytic System
As the name suggests, this system is also anaerobic but uses glucose and glycogen from the muscles as it’s fuel source. This system will produce ATP rapidly, but not as rapidly as the Phosphagen system. It does, however, produce ATP for longer bouts of activity, usually lasting 35-60 seconds depending on your fitness levels. This system is only capable of the partial breakdown of glucose and there is still energy available after the production of the ATP. It is therefore an inefficient and wasteful system.
Oxygen Dependent Glycolytic System
This system is considered the complete glycolytic system as the glucose/glycogen is completely oxidized in the production of ATP, with no waste products. This system can produce a lot of ATP from one molecule of glycogen, but it requires over 25 different chemical reactions. This makes it a much more efficient system capable of producing large amounts of ATP for a longer duration of between 1 and 40 minutes. The problem is that it can’t produce ATP rapidly enough for short duration bursts of energy needed for sprinting or high-intensity muscle contractions. This system is aerobic, meaning it uses oxygen along with glucose to generate ATP.
Oxygen Dependent Lipolytic System
The final aerobic system uses the breakdown of fat, or lipids, to produce ATP. One molecule of fat can produce more ATP than any of the other systems without resulting in muscular fatigue. This system is for long endurance or lower intensity activities and can last for 40 minutes or longer. This system is only used at lower intensities, typically at around a heart rate of 110-130 beats per minute.
Piecing it all together: Training for fat loss
People who want to lose body fat are usually told to do low intensity cardio-vascular work. This is because they will primarily use the Oxygen Dependent Lipolytic System, which uses body fat as its fuel source. It is rationalized that any higher intensity exercise would use one of the glycolytic systems and not burn body fat, but instead deplete muscle glycogen.
Not much fun and not effective for fat loss
On the surface this is actually true, because an hour of low intensity exercise will burn more fat that an hour of high intensity exercise because the former uses fat as its fuel source and the latter uses glucose as its fuel source. This is why you have been told to train in your low intensity ‘fat burning zone’ for fat loss.
The problem with this reasoning is that the bigger picture is not considered. You need to look at the other 23 hours in the day when you’re not training to determine which method is best for fat loss. There are three reasons why training at a high intensity and heart rate will be more beneficial in the long run.
Firstly, if exercise has been done in the glycolytic system at a high intensity, the depleted glycogen in the muscles will need to be replenished from the food that you eat after exercise. This is not the case if the exercise was done in the lipolytic system in your fat burning zone because the glycogen supplies were not depleted and therefore don’t need replenishing. As a result, any excess energy consumed will be stored as fat and not used to replenish glycogen in the muscles.
This brings me on to the second reason why high intensity training kicks butt. Training at a higher heart rate, in the glycolytic system, will burn a greater total number of calories during exercise than at a low intensity. True, the calories come from a different source, but at the end of the day it doesn’t really matter. Remember, in order to lose weight total calories consumed must be less than total calories burnt, regardless of whether it’s fat or carbohydrate and at a higher intensity you’re burning more calories. Period.
I’ve saved the most important point for last though and that is the hugely increased metabolic rate you get from training in the glycolytic system, which will keep the metabolism elevated for up to 24 hours after you exercise. This is because the high intensity stuff puts your body under tremendous stress and recuperating from that requires a lot of energy for quite a long time.
Finally, how to apply all this information
This is what makes the Tabata Method such a great fat loss protocol. Another method, called HIIT training (High Intensity Interval Training) is slightly less brutal than the Tabata Method, but follows the same principle and is equally effective.
The stationary bike: your friend for HIIT training
Using the HIIT method, you will alternate between exercising hard for a period of time, say 30 seconds, and then recovering at a lower intensity for an additional 30 seconds using whatever method of training you would usually use for cardio-vascular training, be it cycling, running or swimming. Using this method of training you are able to boost your metabolism for a longer period of time post exercise and burn the most number of calories whilst exercising. I’ll write a more in depth article on HIIT training in the near future.
To wrap up, if you don’t feel inclined to do HIIT training or the Tabata Method, you can still benefit from performing your cardio training at a higher intensity, just at a fixed level of effort. This won’t be quite as good, but still effective. Also, before I get demonized for bashing good ‘ol fashioned cardio, there is nothing wrong with it. In fact you can and should still include a little in your fat loss attack, but the worst thing that you can do is intentionally perform your cardio at a really low intensity, because you’ve been told that you need to stay in your fat burning zone. Step it up a notch and enjoy the benefits of effective fat loss training.