You eat food, your body converts the energy in food to adenosine triphospate (ATP) and then your body uses the ATP to fuel your physical activity every moment of every day. That's energy systems in a nutshell. Maybe you could go your entire life without knowing more about energy systems and you'd never know what you're missing; however, knowing a little more about the three metabolic energy pathways could help you get the best results from your workouts. Also, if you know what type of energy system your workout uses, you can properly fuel your workouts. According to Experience Life, each system uses different fuel at a particular rate, which affects muscle gain and fat loss in certain ways. Learn more about your body's energy systems so you can reach your fitness goals faster without wasting time or energy. (via Live Strong)
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The Phosphagen System, also known as the adenosine triphosphate-creatine phosphate (ATP-CP) system, supports high power, short duration exercises. This system is your energy reserve for emergencies. Your body uses ATP (your energy life source) constantly, which is why you can't just eat once during the day and expect your body to function properly. You need energy all day long. A little bit of ATP is stored away in your muscles for those moments when you need a quick burst of energy. For instance, the phosphagen system will kick in when you see your child about to fall off his or her chair and you jump up and across the room to catch her. This system only stores enough energy for six to ten seconds of hard exercise so that's things like swinging a golf club, lifting heavy weights or sprinting and while it doesn't burn a ton of fat or build lots of muscle, it's essential to maintaining your quick reaction time in daily life. (via Experience Life)
The Glycolytic System kicks in when your ATP-CP system is spent. This system supports moderate power for short periods of time. Exercising the glycolytic system is painful but the more you train it, the faster you can recover between sets of exercise. This exercise includes things like sprint intervals during which you take brief rest periods between that don't let you fully recover before going at it again. Training that improves the glycolytic system builds muscle mass and burns fat even during recovery. (via Breaking Muscle)
The Oxidative System is always at work in your body, even when you sleep. It requires oxygen to function so if your oxidative system fails, your body will stop functioning. This system supports long-distance sports that call for strong endurance. The more you train, the better your aerobic metabolism and the more effectively your body burns fat during your workouts. When you hear about EPOC (excess post-exercise oxygen consumption, you're hearing about your oxidative system working up to two days after an intense workout. Oxidative training is great as a recovery for other intense workouts or a good workout on your off day. It is the most important energy system and if it doesn't work, your body doesn't have oxygen.
>> Read more: Own Your Next Workout With Better Endurance
According to ACE Fitness, all three of these systems work together to provide energy to your physical activity. While none of them work alone, they each dominate at different times during certain exercise. Exercise physiologists have studied exercise and the body to create workouts that achieve maximum results for your efforts. This is just the tip of the iceberg. Understanding your body is important to achieving your goals so dig in! Read about your heart rate during your workout.