As we’ve discussed previously, no physical fitness program can be accomplished efficiently and effectively without a good sound nutrition plan. One must learn to balance their intake of the energy nutrients (protein, carbs, and fat). Remember, try to go for the best sources of each of the energy nutrients. When consuming carbohydrates, be aware of what types you are consuming. Fiber is best for you, followed by complex carbs, then lastly simple carbs. Try to stick with high quality, low fat protein sources like chicken, fish, lean beef or pork, whey protein, egg whites, etc. Next, watch your dietary fat intake. Try to keep the amount of fat daily that you consume between 20 and 30 percent. Finally, find a good multivitamin and drink plenty of that all important substance water. Now that you’ve got a good nutritional plan, you’re ready to start thinking about exercise.

When considering a good exercise plan, many questions come to mind. Should I lift weights or do aerobics? What about running or swimming? How often should I work out? How many times per day? How many sets/reps? What are the best exercises to do? These are just some of the question that will be covered in the next few issues of Semper Fitness. However, this issue we’re going to discuss the difference between aerobic and anaerobic exercise.

Before we talk about aerobic and anaerobic systems, we must explain a molecule called ATP or adenosine triphosphate. For our purposes, ATP is the body’s energy source, just as gasoline is the energy source in an automobile engine. How quickly and efficiently a muscle cell produces ATP determines how much work the cell can do before it fatigues. While there is some ATP stored in a muscle cell, the supply is limited. Therefore, muscle cells must produce more ATP in order to continue working. Muscle cells replenish the ATP supply using three distinct biochemical pathways, or separate systems of chemical reaction: the aerobic system, anaerobic glycolysis and the creatine phosphate system. The aerobic and anaerobic energy systems will be discussed during this issue.

The word "aerobic" means "with oxygen." The first system for producing ATP, the aerobic energy system, is dominant when adequate oxygen is delivered into the cell to meet energy production needs, such as when the muscle is at rest. Most cells, including muscle cells, contain structures called mitochondria. The mitochondria are the site of aerobic energy (ATP) production. The greater the number of mitochondria in a cell, the greater the aerobic energy production capability of that cell. The other two energy systems, anaerobic and creatine phosphate, are the primary sources of ATP when an inadequate supply of oxygen is available to the cell to meet its energy needs. In the absence of sufficient oxygen, as when a muscle needs to generate force quickly (lift heavy weights), the muscle relies primarily on the anaerobic system which provide a rapidly available source of ATP. "anaerobic" means "without oxygen." The anaerobic production of ATP occurs inside the cell, but outside the mitochondria.

Most cells, such as those in the heart, brain and other organs, have little or no anaerobic capability. Therefore, these cells must be continuously supplied with oxygen, or they will die. For example, if a coronary artery (which supply blood and oxygen to the heart muscle) becomes clogged with a build-up of cholesterol deposits, there will be a diminished flow of blood through that artery (ischemia). The decreased blood flow can lead to an insufficient oxygen supply to the heart muscle, during rest or exercise which often leads to a sensation of pain and/or pressure in the chest called angina pectoris. If the oxygen supply is cut off, such as when a blood clot forms where the coronary artery has become clogged, the area of the heart muscle beyond the blockage suffers a "heart attack" (myocardial infarction). In the brain, ischemia can lead to a stroke.

Unlike the heart and the brain, skeletal muscles such as the triceps and quadriceps, have a significant anaerobic capability. You must understand aerobic and anaerobic energy production in relation to what substances are used to produce ATP. I’m not going to go into all of the technicalities, however, a basic understanding of the process will help you in designing a good exercise regimen.

Fat (fatty acids) and carbohydrate (glucose) are the two substances the body’s cells use to produce most of the ATP supply. Proteins, which are comprised of various combinations of amino acids, are not a preferred energy source. In an adequately nourished person, proteins play a minor role in energy production. However, when the diet does not supply sufficient calories, the body is capable of using amino acids, stored in tissues such as muscle, to produce the energy it needs. This is definitely not an ideal process.

When the body is at rest, the cardiopulmonary system is easily able to supply adequate oxygen to the mitochondria of muscle cells. Both glucose and fatty acids are used to produce ATP. With increasing exercise intensity, the cardiovascular system makes every attempt to increase its delivery of oxygen into the mitochondria of exercising muscles to aerobically produce enough ATP. At some point, the cardiovascular system becomes unable to supply enough oxygen to the exercising muscles, so they call on the anaerobic systems to rapidly produce ATP. You must understand that the anaerobic system cannot predominate for a prolonged period. The primary source of anaerobic ATP production is glucose, which is carried in the blood and also is stored in muscles and the liver as glycogen (large molecule made up of chains of glucose). To help you better understand why the anaerobic system cannot keep going for a prolonged period of time all you have to do is think of what happens when you do an exercise like the bench press or some other heavy weight lifting exercise. With the heavier weight, you can’t keep lifting it for any extended period of time. The muscles become fatigued quickly.

Let’s put it all together for the big picture. As long as a muscle cell is aerobic, it uses both fatty acids and glucose to produce ATP. The aerobic system produces much more ATP than the anaerobic systems, primarily because fat yields nine calories of energy per gram, while carbs and protein only yield four calories per gram. further, the end products of aerobic ATP production are water and carbon dioxide. Both are relatively easy for the body to deal with, so that aerobic energy production does not lead to muscle fatigue quickly. When exercising muscle becomes anaerobic, it relies on glucose mainly (and to a limited extent the phosphagen system) to produce ATP. However, not only is much less ATP produced anaerobically than aerobically per molecule of substrate used, the by-products of anaerobic ATP production include lactic acid, heat and hydrogen ions. As the level of lactic acid and other by-products increases in a muscle, continued contraction of that muscle is soon inhibited. Lactic acid is thought to be the principal cause of the immediate soreness (the burn) in an exercising muscle.

This should give you a pretty good understanding of the aerobic and anaerobic systems and how they produce ATP. Store this info in your brain’s fitness databank for future use. Then stay tuned in for our next issue, where we start to split up the different systems and talk a little about the benefits for each one. That’s the scoop from Semper Fitness. Stay pumped, stay motivated and OO-RAH!

Semper Fidelis!