Energy metabolism fuels every exercise you do—from running marathons to lifting weights.
The body uses three different systems of energy metabolism: the phosphagen system, the glycolysis system, and the aerobic system. These systems work in harmony to create molecules of adenosine triphosphate (ATP), the body’s usable form of energy.
Your cells do not store a huge supply of ATP molecules, so once you start contracting your muscles, you deplete your supply of ATP pretty quickly. Your cells are forced to start making more ATP to power your body immediately.
The phosphagen system
When your body needs ATP, you first use the ATP stored in your muscle cells. According to the Science Learning Hub, this energy stored for exercise only lasts three seconds.
Afterward, your muscle cells use their first system of energy metabolism, the phosphagen system. This process breaks down stored phosphocreatine to generate ATP. This energy provides another eight to ten seconds.
The glycolysis system
Once your muscle cells run out of phosphocreatine, they switch to the second system of metabolism known as the anaerobic glycolysis system. This process uses large stores of carbohydrates (stored in the body as either glycogen or glucose) to rapidly make more ATP—without the need for oxygen.
The ATP produced lasts roughly 90 seconds, providing just enough energy for anaerobic workouts, like lifting weights or sprinting.
The aerobic system
If your muscles need more ATP to endure a longer-lasting activity, the third system of metabolism, aerobic respiration, kicks in. This process breaks down your body’s glucose and fat reserves (created from carbohydrates, fats, and proteins consumed in the diet) to produce enough ATP to last several hours.
This is why extended exercises like running, dancing, swimming, biking are called aerobic workouts.
Where do you get the energy?
Every cell in your skeletal muscles contains anywhere from a few to thousands of mitochondria, tiny organelles widely known as the “powerhouses of the cell.” The mitochondria convert the energy stored in food into ATP.
However, your mitochondria cannot produce ATP or generate enough energy for you to even snap your fingers without one important coenzyme, NAD+—nicotinamide adenine dinucleotide. In a systematic review published in Skeletal Muscle, the need for NAD+ in muscle development is well-documented.
As stated in the abstract, “The vast majority of studies indicate that lower NAD+ levels are deleterious for muscle health and higher NAD+ levels augment muscle health.”
All three systems of energy metabolism depend on NAD+.
In the anaerobic glycolysis system, NAD+ allows cells to oxidize glucose to pyruvate and quickly generate small amounts of ATP.
In the aerobic respiration system, NAD+ extracts even more energy from sugars and fats and then reacts with proteins in the inner membrane of your mitochondria to drive the production of large amounts of ATP.
In the phosphagen system, NAD+ is used to recharge after a workout. ATP produced with help through the aerobic and anaerobic systems recharges spent phosphocreatine.
Support your mitochondria for better exercise
If you’re looking for ways to support your physical endurance, running time, energy, and limit muscle soreness, you want to make sure your mitochondria continue to churn out ATP molecules.