Ever wonder how our body has the energy to jump, to lift, to push, to pull, to walk, etc? This will explain how that works, and how we can perform our best in and out of the gym and how we can utilize these systems to burn fat.
Yes, the foods we eat provide the calories that are turned into energy (adenosine triphosphate or ATP) for the body, but when we eat foods, they are broken down into amino acids, fatty acids or glucose and the either sent down a metabolic pathway or stored for later “use,” through one of these energy systems.
The first is the phosphagen system. This utilizes creatine phosphate to quickly replinish ATP to the muscles, but our muscles cannot store much creatine phosphate or ATP so its very limited. It’s the energy system used in the very beginning of our workout routine, or very short term high intensity activities lasting up to 30-60 seconds.
It also takes a few minutes to restore, up to five minutes, even. Think about doing heavy triples on back squats with a good amount of rest between sets or how great your first five or six burpees feel in a set of 20+. These are utilizing the phophagen system to get energy to your muscles.
It should also be noted that type II muscle fibers (think larger muscles, big movers like quads and glutes vs triceps or abdominals) are capable or storing more creatine phosphate as well as ATP, so you are going to see this expressed more often in 50 yard sprints or squats rather than something like sit ups.
The second energy system is glycolisis, which can be broken down into two sub-systems, anaerobic (does not necessitate oxygen) and aerobic (necessitates oxygen.)
Anaerobic glycolysis breaks down glucose into a useable form of energy to produce ATP fairly quickly (not as fast as the phosphagen system can, but still fast because it doesn’t require oxygen) but again, is limited. This would be the energy system utilized for an activity that can only be sustained for about 30-60 seconds. Examples could be something like a 100m sprint or a max effort set of bench press.
Aerobic glycolysis requires oxygen to produce ATP and is associated with slightly longer activities after the phophagen and anaerobic glycolysis systems have fatigued. This system utilizes glucose to produce limited amounts of ATP (more than the phosphagen system though) but slightly more efficiently. This will be our working energy system for about 1 – 3 minutes, so examples may be a 400m sprint or a three minute AMRAP of burpees.
Our final energy system is the oxidative system, the only system that utilizes amino and/ or fatty acids as fuel, in fact 70% of the energy used to create ATP comes from fat, 30% is from glucose but there is potential to utilize amino acids if we are in a catabolic state, but that’s another blog for another time.
The oxidative system is what we are using when we are doing an activity we need to sustain for 3 minutes or longer, like a mile jog or a workout like 50-40-30 sit ups, squats and push ups, or a yoga class. The lower the intensity, more fatty acids are used.
So what does this have to do with fat loss?
First it should be noted and utilizing all three energy systems is good for our heart, our lungs and for fat loss and muscle building, and chances are if you are following a complete workout program, you are utilizing all three energy systems at some point.
For example, if you begin your program with a quick warm up of jumping jacks, air squats and deadbugs, those first few seconds you are utilizing the phosphagen system, as you progress through your warm up, you move into the glycolysis system. Then if your first exercise is 5×5 bench press, as you hit your sets of 5 bench you are utilizing the phosphagen system because you notice as you go heavier and heavier you need 2-3 minutes to recover.
Then you may have some accessory work like a couple of supersets of bent over rows and tricep kickbacks, which is utilizing the glycolysis system. Then at the end you have a little cardio piece of a 10 minute AMRAP of inverted rows and burpees, in which case you move into a oxidative system. Or perhaps the next day you simply go for a 4 mile walk for active rest, which is again oxidative.
But if you want to lose fat, all three can be utilized because..
The phosphagen system allows you to challenge yourself with heavy lifts. heavy lifts are what are necessary to build muscle and the more muscle you have, the easier it is to lose fat and see visible muscle.
The glycolytic system allows you to do very quick bursts of activity, followed by rest. This is what HIIT training truly is and this is the best way to do cardio without risking burning any of your hard earned muscle.
And the oxidative system is what helps you burn more fat than anything, so if you really want to lose fat, go for a 30 minute walk, and keep the intensity lower.