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What is ATP? Do we need ATP, and what should gym-goers consider to maintain stable ATP levels in the body?
Defining ATP: What is it?
ATP: The Essential Energy Source for Muscles and Cells
During ATP hydrolysis, ADP (Adenosine Diphosphate) and an inorganic phosphate group are formed, releasing 12K calories of free energy.
ATP reserves in a muscle bundle are limited. For long-term muscle function, ATP must always be fully replenished. Energy used to replenish ATP comes from the breakdown of various substances: starch, protein, fat.
In the body, ATP is synthesized through two different pathways:
The absence of oxygen involvement is termed as the anaerobic process.
The presence of oxygen involvement is termed as the aerobic process.
To regenerate ATP, there are three energy systems (energy pathways) at work:
Among them, the phosphagen and lactic systems are anaerobic, while the oxidative system is aerobic. These three systems differ in:
+ Physique: the substance that generates energy.
+ Capacity: the maximum quantity that can be supplied.
+ Power: the maximum energy source that can be supplied within a certain period.
The involvement level of the three energy systems depends on: muscle contraction power and duration, muscle activity conditions, and the level of oxygen supply to the body.
The POWERHOUSE of energy: PHOSPHAGEN system
ATP expenditure in muscles can be swiftly replenished thanks to creatine stored within (creatine phosphate), hence this energy system is also known as ATP-CP. Let's keep it simple and easy to grasp without delving into cellular mechanisms.
Phosphagen is the fastest energy supplier for the body, utilized in the initial phases of muscle activities. It boasts the highest power output, surpassing lactic and aerobic systems by threefold and fourfold respectively. Therefore, Phosphagen system predominantly fuels high-power activities: sprinting, throwing, pushing, jumping... Its energy delivery is extremely brief (not exceeding 12s), hence longer activities necessitate involvement of other energy systems.
The LACTIC system
For relatively longer activities, the body utilizes energy to replenish ATP and CP by breaking down reserved glucose stores, resulting in the production of lactic acid, causing muscle fatigue. Hence, this energy system is named the Lactic system.
The essence of this energy system lies in glycogen stored in muscles, with blood glucose transferring into muscles and glucose from the liver moving into the bloodstream.
This system operates at a lower capacity compared to the Phosphagen system (less than three times the Phosphagen system and more than 1.5 times the Aerobic system).
During maximum activity, glycogen breakdown only accounts for up to 25% of the reserved glycogen amount. Consequently, the capacity of the Lactic energy system is not substantial.
This energy system kicks in right from muscle contraction but reaches its peak power after 30-40s. Therefore, the Lactic system plays a decisive role in supplying energy for activities lasting from 20s to a few minutes.
During Lactic system activity, glycogen levels in muscles and the liver are never depleted. The limitation of Lactic energy is not due to low glycogen reserves but rather the production of lactic acid inhibiting glycogen breakdown enzymes.
The Oxygen energy system
In low-power, prolonged muscle activities with sufficient oxygen supply, namely aerobic activities, the body utilizes oxidative reactions of nutrients such as sugars, proteins, and fats to fuel its movements. This energy system is known as the oxidative system.
This oxidative energy system utilizes two primary substances: sugars and fats to fuel muscle contractions. These substances differ significantly in power and capacity.
Sugar oxidation: occurs similarly to glucose hydrolysis in the Lactic system. As this process involves oxygen, lactic acid produced continues to be oxidized into CO2 and water.
The capacity of the sugar oxidative system depends on glycogen reserves in muscles and the liver, as well as the ability to regenerate glucose from other substances (lactic acid, amino acids, pyruvic acid...) by the liver with substantial capacity.
On the other hand, fat oxidation yields more energy than sugar oxidation. Since the body stores a significant amount of fat (on average 10%-30% of body weight), it provides enough energy for continuous bodily activity for several days.
The ratio of sugar and fat oxidation depends on the intensity of aerobic activity. Higher intensity favors sugar oxidation, while lower intensity favors fat oxidation.
SUMMARY
| Time (seconds) | Activity Classification | Energy Supply from |
| 1-5 | Aerobic | ATP (stored in muscles) |
| 5-10 | Aerobic | ATP + CP |
| 10-45 | Aerobic | ATP+CP+Glycogen |
| 45-120 | Aerobic + Lactic | Glycogen |
| 120-240 | Aerobic + Anaerobic | Glycogen + Lactic |
| >240 | Anaerobic | Glycogen + Fat |
CONCLUSION
Through this article, you've grasped the essence of ATP and the functioning of the 3 energy systems in ATP synthesis for muscle activity. Now, you can apply this knowledge to your workout sessions for optimal results. Wondering which energy system to use for muscle gain? Weight loss? Body fat reduction? Surely, you've answered these questions yourself. Goodbye and best wishes for success.
Posted by: Fish Fryer
Keywords: What is ATP? Why is it essential to maintain ATP levels during Gym workouts?
