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Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.
Whether you step out of your house for a leisurely walk around the neighborhood, join in with your friends for a backyard volleyball game or run a marathon, you are engaged in physical activity. 'Physical activity' is a broad term that is defined as any movement of your muscles that requires energy. The raw energy that allows you to be active comes from eating the three energy-yielding nutrients - carbohydrates, proteins and fats - along with some potential energy reserves stored in your body. But the raw energy you get from these sources is not in a form that is usable by your body, so before your body can benefit from these energy sources, their energy must be converted into the form your body likes - namely adenosine triphosphate, which is better known as ATP. ATP is the form of energy your body uses to perform bodily functions. ATP is a high-energy-containing molecule, and it might help if you think of ATP as your body's fuel, much like gas is the fuel used by your car. In this lesson you will learn how your body gets ATP from the available raw energy sources so you have fuel to meet your energy needs during periods of physical activity.
The energy-containing molecule ATP can be made by your body in the presence of oxygen or in the absence of oxygen. We use the term anaerobic metabolism to describe energy creation in the absence of oxygen. This is a fairly easy fact to remember if you recall that the prefix 'an' means 'without' and the word 'aerobic' refers to 'oxygen,' so anaerobic metabolism allows your body to generate usable ATP without oxygen.
This is handy when you need a sudden burst of intense exercise or for the first few minutes of exercise when your body is still catching on that you upped your physical activity level. For example, when you lace up your jogging shoes and head out the door, your muscles move from a relatively sedentary state to an active state. This increase in activity requires more energy, but your heart and lungs have not yet had time to increase the amount of oxygen available.
Fortunately, your muscles have a small reserve of ATP in storage and you don't need any oxygen to retrieve this energy. Of course, the key word here is 'small' because this reserve of ATP is used up after only a few seconds of activity. Yet you do not crash because you have another energy-containing molecule stored in your muscles that can be broken down easily to make ATP called creatine phosphate (CP).
Did you notice that the word 'phosphate' is contained in both 'adenosine triphosphate' and 'creatine phosphate'? That's an important observation. In fact, you might want to think of creatine phosphate as a phosphate donor that gives broken-down ATP new life. You see, when your body needs energy it breaks down ATP. This process involves the ATP molecule giving away one of its three phosphate groups (notice that it's adenosine triphosphate, which means it has three phosphate groups). After the ATP molecules from your muscle break down, creatine phosphate jumps to the rescue and donates its phosphate group. This regenerates ATP, allowing your activity to continue.
Great system! But, there's a catch; you don't have much creatine phosphate in storage, so it isn't more than about 15 seconds until your muscles are empty. If your physical activity continues, your muscles must get more energy, but your heart rate and breathing have still not had enough time to boost oxygen levels. So your muscles must make more ATP anaerobically. This stage of anaerobic metabolism makes ATP very quickly, but it can only use glucose to make the molecules. Glucose is simple sugar that your body gets from breaking down the carbohydrates that you eat. You also have some stored glucose in your muscles called glycogen that can be used to make ATP in this way.
It's amazing how your body keeps coming up with quick ways to supply you with energy for your physical activity, but I hate to say that this system also has its drawbacks. First of all, this is a fairly inefficient method of energy production, as every molecule of glucose produces only two molecules of ATP. Secondly, the process results in lactic acid production. You can think of lactic acid as an end product of anaerobic metabolism, and if you don't get oxygen soon, it will also end your exercise session. This is because high levels of lactic acid can interfere with muscle contractions and produce muscle pain. This lactic acid build up limits your energy system, requiring you to either stop or greatly reduce your intensity.
Now, if you think about it, if you reduced your intensity, it would give you a chance to catch your breath - or, more specifically, it would allow your breathing and heart rate to catch up and supply oxygen to your muscles. With this oxygen, you can move into the longer-term energy production system called aerobic metabolism, which is simply energy creation in the presence of oxygen. This system is not as fast as anaerobic metabolism, but it is much more efficient, making up to 15 times more ATPs per glucose molecule.
Better still, aerobic metabolism can call on the two other energy-yielding nutrients, fats and proteins, to make ATP. Have you ever heard of body fat being referred to as stored energy? That's because it is! Fat contains a lasting supply of fatty acids. If you exercise for a long time at a low to moderate intensity, fatty acids become your primary source of fuel. Proteins can also be called on to make ATP, but proteins are very important to your body, so your body doesn't like to burn them up for fuel, and therefore, they are not a major source of energy. Yet the building blocks of proteins, which we call amino acids, can be converted into ATP through aerobic metabolism, especially if something extreme is going on, like you're starving or you are involved in high-endurance exercise.
'Physical Activity' is defined as any movement of your muscles that requires energy. You get raw energy from the three energy-yielding nutrients - carbohydrates, proteins and fats - along with some potential energy reserves stored in your body. This raw energy must be converted into adenosine triphosphate, or ATP, which is the form of energy your body uses to perform bodily functions. This can be done in the presence of oxygen or without oxygen. Anaerobic metabolism is energy creation in the absence of oxygen. Your muscle has a small reserve of ATP in storage that provides energy for a few seconds of activity. When that's used up, your muscles call on creatine phosphate, which is an energy-containing molecule stored in your muscles that can be broken down easily to help make ATP. Creatine phosphate does this by donating a phosphate group to the broken-down ATP molecule, giving it new life. This can provide energy for about 15 more seconds. If your physical activity continues, your muscles continue to make ATP via anaerobic metabolism by using the simple sugar glucose to make ATP. The drawbacks of this process are that it is inefficient and it results in the production of lactic acid, which is an end product of anaerobic metabolism.
If you continue exercising at a low to moderate intensity level, your breathing and heart rate have time to catch up and supply oxygen to your muscles. This allows aerobic metabolism, which is simply energy creation in the presence of oxygen, to kick in. This system is not as fast as anaerobic metabolism, but it is more efficient. We also see that aerobic metabolism can use glucose, fatty acids and amino acids to make ATP.
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Back To CourseHealth and Wellness
11 chapters | 101 lessons