Our Body's Energy Pathways
In this article we will look the three basic energy systems. Having a basic understanding of how the body will replenish itself for energy will help with your sporting performance or fitness goals.
During daily activity, working lives, or more specifically to this blog for exercise, our bodies require energy to operate. The main ingredient required for energy is adenosine triphosphate or, ATP. Focusing on exercise, it doesn't matter whether you're running a marathon or using one massive short explosive movement, our muscles are powered by ATP. We can only store a small amount of ATP within our cells. In fact there's only enough for a few seconds so it goes without saying that the body must somehow replace or, re-synthesize, the ATP in a continuous cycle. Understanding the energy systems will give you a good understanding or how the replacement of ATP occurs once it's been used. This will also give you the knowledge of which energy system, or systems are used in you chosen sport or when you train for health and fitness.
Before I explain the 3 basic energy systems I mentioned earlier, let's take a look at what ATP is made up of. An ATP molecule consists of adenosine and three, this is where the 'tri' comes from, phosphate groups. As we exercise, the last phosphate group splits away and releases energy. The molecule of adenosine triphosphate now becomes adenosine diphosphate or, ADP.
As I mentioned we need to now replace the missing molecule to replenish our body's limited stores of ATP. Chemical reactions add a phosphate group back to ADP to create ATP. This process is called phosphorylation. If this occurs in the presence of oxygen it is labelled aerobic metabolism. If it occurs without oxygen it is labelled anaerobic metabolism.
So how do we replace the used ATP with the sources available and how do they relate to the different levels of exercise intensity.
The Anaerobic (ATP-CP) Energy System
The ATP stores in the muscle last for about 2 seconds and the re-synthesis of ATP from Creatine Phosphate or, CP will continue until CP stores in the muscles are depleted after about 4 to 6 seconds. This gives us around 5 to 8 seconds in total of ATP production.
ATP -- ADP + CP = ATP
To develop this energy system, sessions of 4 to 8 seconds of high intensity work at near peak velocity are required.
The Anaerobic (Lactate) System
If the body must continue to work longer than 10 seconds there must be another energy pathway to allow the regeneration of ATP. Once the CP stores have been depleted the body needs to call on stored glucose for ATP. Glycogen can be used to form ATP, and in the liver it can be converted into glucose and transported to the muscles via the blood. A heavy training session can deplete carbohydrate stores in the muscles and liver, as can a restriction in dietary intake. This energy system is the second quickest available to replenish ATP.
Aerobic System
The aerobic energy system utilises proteins, fats and carbohydrate (glycogen) for re-synthesising ATP.
Fat
Fat is stored predominantly as fatty tissue throughout the body and is a substantial energy reservoir. Fat is less accessible for metabolism as it must first be reduced from its complex form, triglyceride, to the simpler components of glycerol. So although fat is a vast stockpile of fuel, energy release is too slow for very intense activity.
Carbohydrate
Unlike fat, carbohydrate is not stored in peripheral deposits throughout the body. At rest, carbohydrate is taken up by the muscles and liver and converted into glycogen. Glycogen can be used to form ATP and in the liver it can be converted into glucose and transported to the muscles via the blood.
Protein
Protein can be used as a source of energy, particularly during prolonged activity; however it must first be broken down into amino acids before then being converted into glucose. As with, fat, protein cannot supply energy at the same rate as carbohydrate. There are a few factors relating to the rate at which protein is used. For example, if there are large amounts of one type of fuel available, the body may rely more on this source than on others. The mass action effect is used to describe this phenomenon.
As I mentioned at the beginning this is to give a basic understanding of the body's energy systems and how they relate to different sports or exercise intensity. I hope this helps those who are interested in this side of fitness. Along with mental toughness, understanding this can go a long way to you achieving your goals, or crumbling when it matters most.
Thanks for reading!
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