The human body has 3 energy systems it uses during workouts, which are producing force to overcome challenges and work as a sliding spectrum. Sometimes the three of them work simultaneously.
Aerobic system - This is your body’s default system which is used daily. It’s referred to as the oxidative energy system because it’s your oxygen tapped into fat.
We use this system all throughout the day, in everything we do, and how much we burn depends on many different factors like our health, the food we eat, and our fitness level.
It takes 20 minutes of exercise at a steady pace or short bursts of high intensity a day to train it.
Phosphagen system (ATP-CP) - This system uses creatine phosphate (CP) to release adenosine triphosphate (ATP) for quick bursts of power or speed.
Your efforts are limited to about 10 seconds since your muscles store very little ATP and CP. Then, you have to allow your muscles to replenish their phosphagens.
It takes relatively short bouts of near-maximal effort to train it.
Anaerobic glycolysis - This system gets the glucose from your blood along with the glycogen stored in your muscles and liver. We use it for anything that takes more than 10 seconds and creates an oxygen deficit by the end, at the beginning of lower-intensity activities, before our breathing stabilizes, and we can use our aerobic energy system, and at the end of the workout.
The combination of interval training and strength can help your clients improve conditioning, and by that allowing them to perform longer and more challenging sets and recover faster in between.