If you want to get stronger, leaner or just generally in better shape you should begin with knowing the body. I do not think it is necessary to have a Phd in order to train, yet you should understand the basics of what you are doing. With that said I am going to touch on the basics of the three energy systems and give you a short example of each.
Before I delve into these understand that this is a very surface view of the three systems As with anything dealing with the human body these systems are not black and white and there is always some movement between them.
The first energy systems is referred to ATP/PC system. This system lasts for about 7 seconds of hard work. The easiest way to think about this system is if we were to do a 100 meter dash after about 6-7 seconds your body would begin to decelerate. If you look at the best 100 meter sprints of all time they all begin to decelerate around 60-70 meters. This is when the body must move from ATP/PC into the second energy system.
How does this apply to us? Anything we do for low reps would tend to fall into this system. plyometrics, explosive lifts or even a heavy single. This energy system is great for getting strong and explosive yet the total energy output isn’t great enough to create a huge caloric deficit so generally we will train this system on the first big lifts before we move into the other energy systems.
The second energy system is glycolysis. Without getting too scientific this is the system in which the body must take muscle glycogen and turn it into usable energy. The great part about this systems is it can be a huge tool for burning immense amounts of fat. Muscle glycogen is always sitting and waiting to be used. Once the glycogen is used up the body replenishes this with liver glycogen. I hope you are starting to see that this system has more processes and burns more calories.
Ironically, while glycolysis burns more total calories it also burns less fat and this is actually a good thing. This is the energy system that puts us in a calorie deficit and continues to burn more calories after the training session.
The way we train this energy system is anything that takes 30-60 seconds. So if you ever do repetition work and it burns that is the byproduct of this energy system. 12 pull ups would fall into this energy system as would 45 seconds of rows or anything for time. For a good variation use time for your accessory work instead of reps. One of my favorites is pick an exercise do it for 60 seconds then rest 60, then do 45 second and rest for 45, then 30/30 and 15 seconds to finish. Two things will happen with this method. First you will feel huge. Second, your body will burn a ton of calories.
The final energy system is aerobic. This is the energy system that burns almost all calories from fat. The downside to this energy system is that while we burn most calories from fat we also don’t create many processes that will burn calories post exercise. This energy system is generally used when we do a slow controlled activity over a long time. Think long slow bike ride or walk/jog. This is actually the energy system that we use as we sleep and sit at our desks.
How do we use this system? This system is best used for recovery as it is a lower stressor on the body. Use this system on an off day to move blood into the tissue without damaging the tissue. If you are a distance athlete I would spend more time in training this system yet if you goals are more diverse then I would use this system more for recovery then for training. The stress is not great enough to create major change.
All three systems are very different and each serves it’s own purpose in the body. When in doubt just work from the top down. Train the first system hard (ATP/PC) move to the second (glycolysis) and finish with some aerobic work. If that is all you do for one hour total work three times a week you would still be in better shape and stronger than most people.
