Wednesday, March 18, 2009

The Biology of Muscle

Contributed by nemo.

In all living cells energy is temporarily packaged within a remarkable chemical compound called adenosine triphosphate (ATP), which holds a readily available energy for very short periods of time. We may think of ATP as the energy currency of the cell. When you work to earn money, you might say that your energy is symbolically stored in the money you earn. The energy the cell requires for immediate use is temporarily stored in ATP, which is like cash. When you earn extra money, you might deposit some in the bank; similarly, a cell might deposit energy in the chemical bonds of lipids (fats), starch, or glycogen. Moreover, just as you dare not make less money than you spend, so too the cell must avoid energy bankruptcy, which would mean its death. Finally, just as you do not keep what you make very long, so too the cell continuously spends its ATP, which must be replaced immediately. Humans use a form of cellular respiration requiring oxygen which is called aerobic respiration. During aerobic respiration, nutrients are catabolized to carbon dioxide and water. The cells of your body use this method to obtain energy from glucose. Glucose is transformed from many different chemicals in the foods you eat. Certain foods contain more glucose than others, which yield more energy. But that doesn’t mean you should eat these foods only, as other low energy foods contain many nutrients your body needs to build muscle, bone, and cells. The following formula shows this process: C6H1206 + 6O2 + 6H2O ฎ 6CO2 + 12H2O + Energy (as ATP) (For you anti-chemistry people) Glucose + oxygen + water gives you carbon dioxide + more water + energy to pull down hard. Aerobic respiration has four stages:
Glycolysis: A six-carbon glucose molecule is converted to two, three-carbon molecules of pyruvate, and ATP and NADH are formed.
Formation of acetyl coenzyme A: Each pyruvate enters a mitochondrion (a tiny body inside of a cell that makes energy) and is oxidized to a two-carbon group that combines with coenzyme A, forming acetyl coenzyme A. NADH is produced and carbon dioxide is released as a waste product.
The citric acid cycle: The acetate group of acetyl coenzyme A combines with a four-carbon molecule to form a six-carbon molecule. In the course of cycle, citrate is recycled to oxaloacetate and carbon dioxide is released as a waste product. Energy is captured as ATO and then reduced as high energy compounds NADH and FADH2.
The electron transport chain and chemiosmosis: The electrons removed from glucose during the preceding staged are transferred from NADH and FADH2 to a chain of electron acceptor compounds. As the electrons are passed from one electron acceptor to another, some of their energy is used to pimp hydrogen ions (protons) across the inner mitochondrial membrane, forming a proton gradient. In a process known as chemiosmosis, the energy of this proton gradient is used to produce ATP. It’s the simplest way I could explain; this is how your body moves, lives, functions. Any cell in your body goes through this process if it wants to do its job correctly. At any one time there are trillions of molecules of ATP being used up. Yes, that is trillion, with this many zeros; 000,000,000,000,000. And that is the basics of how your body has the energy to move. Now, with the normal process I just told you about, each reaction produces about 34-38 ATP molecules. This is the normal rate of production of ATP and is what you would like. There are circumstances, though, when your cells need more oxygen then the body can supply. And as I stated earlier, normal cellular respiration requires oxygen to carry out the production of ATP. When this begins to happen, the cells immediately switch over to a process that doesn’t need oxygen to produce ATP, you notice a burning in the muscles, and you might feel a little “off.” This is a lactic acid build up from an emergency production of ATP called fermentation. And this is a very inefficient process. Each time it goes through the motions, it only creates 4 ATP molecules. But, in return for these measly 4 ATP molecules, it releases a toxin into the body in either the form of lactate or alcohol. Humans can only go on like this for a few minutes before the cells just stop functioning. This is why sprinters can’t sprint for minutes at a time. The cells are not capable of producing the needed ATP to function and, therefore, cease all normal activities. When building strength, everybody seems to have an all-sure solution or the perfect workout. Before I tell you what I suggest, let's look at the basics of muscle structure and work our way up. There are three types of muscle fibers in our bodies: slow twitch (red), medium twitch (pink), and fast twitch (white). Everybody has all three muscle fibers covering their entire body. Some people have more of one type muscle fiber that matches their physical activity. The slow twitch muscle fibers are the thinnest fibers and the weakest. They will also continue to contract the longest. As long as you have adrenaline or glucose to stimulate the muscle fibers they will contract. This is why marathon runners are very thin. They have an abundance of slow twitch muscle fibers and lesser of the medium and fast twitch muscles. Medium twitch muscle fibers are not the weakest nor are they the strongest. They will contract faster and stronger than slow twitch but not as fast or as strong as fast twitch fibers. These muscle fibers will last for around twenty minutes of contraction before they exhaust themselves. Look at the body size of middle distance (mile) runners. They are not thin like marathon runners but not bulky like sprinters. Compare them to fit rock climbers and boulderers. Their body shapes are similar. This is due to the abundance of medium twitch muscle fibers. Fast twitch muscle fibers are the fastest and strongest. Look at sprinters and football players. This is the muscle fiber they build to give them that quick and powerful burst of strength. Since fast twitch is the strongest muscle fiber, it has the shortest endurance. A fast twitch muscle fiber will exhaust itself after thirty seconds of continuous contraction. To drive this point home do one pull up. Hold yourself at the top of the pull up for one minute. Watch the clock as you do this. After close to thirty seconds, you will notice a sudden decrease in strength. This will be your fast twitch muscle fibers giving out and your medium twitch fibers taking over. Your muscles, along with most of your body, are made of protein. Each muscle type is made of a different protein strand. Protein strands are made of different strings of amino acids. As you ingest protein, your body will break it down into the different amino acids contained in that protein. It will then string the amino acids back together to form the protein you currently need. If you have broken down your muscle fibers, your body will take its supply of protein to build to those muscles. If your body does not have an adequate supply of protein, it can't build your weak muscles. It takes a long time for your body to digest protein. Therefore, most protein passes through your system undigested. Think of it as paying high taxes. Of all the protein you ingest you only get to keep part of it. So the more protein you add to your diet, the more protein passes through undigested. But more protein will also be absorbed and broken down by your body. If you want to build strength, your workout should be based around a process of breaking down your muscles and building them back up. Body builders will lift heavy weights and push their fast twitch muscles to the point of total exhaustion and do this for several weeks. They call this their tear down period. Next, they lift with lighter weights for several weeks and allow their muscles to repair themselves. They call this their build up period. During this period, they add as much protein to their diet as they can. You're probably asking, "What about carbs?" Well, carbohydrates have nothing to do with the building of muscle fiber. Protein builds muscle fiber but does not give you the energy to use those muscles. Carbohydrates are chains of sugar molecules. Besides raising your blood sugar, these sugar molecules are used by your endocrine system to produce glucose. Your pancreas then produces insulin to burn the glucose. Glucose is what your body uses for energy when you have exhausted your immediate reserve of adrenaline. Your immediate reserve of adrenaline will last from ten to twenty minutes. If you are not using this reserve of glucose, your body will store it in the form of fat. This is why long distance runners will overload on carbohydrates the night before a big race. They don't continuously take in carbohydrates all the time. So your body will burn energy in the following order. First it uses adrenaline. When your adrenaline is depleted it will burn glucose. When your glucose is depleted, it will make more glucose or glycogen. Where does it get the molecules to make this extra glucose? It comes from that place where your body stored all the carbs you weren't using, in your fat cells. This is how the body burns fat. As a general rule, after twenty minutes of continuous exercise (running, swimming, climbing, etc), your body will deplete its available reserve of adrenaline and glucose. After that, you are burning your stored energy (fat).