You, Me and Energy
Acrobat PDF file can be downloaded here.
We all have grown up with a concept of "body energy". Some of us bubble with energy, others are "worn out". Moreover, from day to day we all experience fluctuations in our feeling of "energy".
Newspapers and magazines are full of advertisements for "energy pills", "energy diets", "energy courses" and you-name-it. The diet supplement industry is huge, the Internet full of endless links and announcements aimed to get you to purchase something to make you less tired, stronger and more enduring. With a "little help", you can become almost invincible without much extra exercising. Glory is just a pill away... Or is it?
These pages are my effort to explain the origin of the energy that drives our bodies, that fuels thoughts, movement, digestion, reproduction and growth; that is to say, all of our physical and mental functions. This might appear to be a huge and complex undertaking but, as we will soon see, the basics are really quite simple. You and I are driven by atomic energy!
What, atomic energy? Me?
Let me begin with a song that I have picked up from the Internet. It is one that I have valued throughout my long career. I have always wanted to include it in a lecture but never had a passing opportunity. So, here comes Michael Flanders and Donald Swann with "Thermal Dynamics". Note that they use "heat" when they really mean "energy". You must click "back" to return to this page after playing the song. Just click here if you want to hear this simple explanation of what energy is.
What are these Laws of Thermodynamics stated simply?
1. The first law of thermodynamics states that the universe's energy is constant; it can neither be created nor destroyed.
2. The second law of thermodynamics states that energy can only be used by moving it from a more active to a less active element.
What does this mean for you and me? Energy is all around us, it does not get "used up" when we "do something". Energy merely moves from us to our environment when we "work". That is, we "lose" energy as heat to our surroundings. All that "eating and breathing" only serves to move energy to us. All that work just moves energy back to the environment.
The Atom and Energy
Now, what has this to do with running the human body on "atomic energy"? OK, let me explain this. First we should look at a few atoms, especially those which are involved in our metabolism. Those are mainly carbon, oxygen and hydrogen.
Here are two drawings of the carbon atom. They show the general construction of all atoms, that is, particles with a nucleus containing protons and neutrons surrounded by shells of swarming electrons. The carbon atom is made up of 6 protons and 6 neutrons in the nucleus and 6 orbiting electrons in two surrounding shells.
What does the oxygen atom look like? Well, oxygen is a colorless gas and carbon is a black powder (or clear solid diamond!) so there must be huge differences in oxygen and carbon atoms. Or...
In truth, the only difference between oxygen and carbon atoms is the number of the "sub-atomic" particles in each of them. Oxygen has two more of every particle than carbon. Oxygen atoms are made up of 8 protons, 8 neutrons and 8 electrons. Otherwise, carbon and oxygen they are quite alike. In fact, the atoms of all of the widely differing elements found in nature differ only in the numbers of protons, neutrons and electrons they are composed of. One exception is found; hydrogen atoms are composed only of one electron and one proton. Hydrogen atoms do not possess neutrons.
We can look at a more modern presentation of an atom in the next figure. Here you can see that protons and neutrons are made up of smaller particles known as several forms of "quarks". I will not go further into this except to point out that atoms are quite unlike our common mental picture of "good solid matter".
I quote: "If we had drawn the atom with correct proportions and the neutrons and protons had a diameter of 10 centimeters:
1. The electrons and quarks would have a diameter of only 0.01 millimeter!
2. The atom would have had a diameter of 10 kilometers!
3. 99.999999999999 % of the atom is empty space"!
This is difficult to accept, but in fact, you and me, our cars, homes and the trees outside are mostly empty space. Furthermore, those atoms that make us up abound with energy.
When we think of atomic energy we usually associate this with energy obtained from the nucleus of unstable atoms, usually uranium-235 or uranium-239. When these atoms adsorb neutrons they split, producing smaller atoms and releasing neutrons and energy as gamma radiation. The neutrons induce further splitting of additional uranium atoms with production of more radiation and heat, the so-called "chain reaction". By controlling the stream of neutrons we can manage the rate of nuclear splitting and heat production. The heat is trapped by warming up water and the steam produced drives generators in much the same way as in coal or gas driven power plants.
The amount of energy stored in atomic nuclei is beyond our "normal" comprehension. An example of this can be seen in atomic weapons. Uncontrolled nuclear division is the basis of these. Release of the energy in around 2 - 4 kilograms of plutonium is equivalent to more than 10,000,000,000 kilograms of TNT. Happily, most atomic nuclei are stable and do not split and release energy. But, that does not mean that the energy is lacking; it is just stable.
Now, this is NOT the energy that drives plants and animals and you and me. However, there is another source of energy in atoms and that lies in the electron shells surrounding the nuclei.
As I have shown you earlier, atoms are comprised of a nucleus surrounded by electron shells. In the cases of oxygen and carbon we find two shells, in hydrogen only one. A "filled" inner shell or orbital contains 2 electrons, a filled second shell contains 8 electrons. These shells are "energetic", that is, the electrons are held in place by energy. Moreover, the further they are from the central nucleus, the more energy they carry. Electrons can "hop" from one atom to another. As Flanders and Swann explained, they always do this by hopping from a higher to a lower energy state unless they get external "help". That is, they move from a shell further from a nucleus to one closer to the center of the "receiving" atom. The energy is released as photons and we sense this as heat or light.
This "electron hopping" is the source for all of the energy used by living organisms. For almost all forms of life, this arises from burning of carbon-based material in air or, more correctly, using the oxygen in air to accept electrons from carbon compounds.
In the following figure you can see how burning takes place. Two elements are required; a reducing agent that is oxidized and an oxidizing agent that becomes reduced. Reduction means gaining electrons; oxidation is loss of electrons. Remember once more the song "Thermal Dynamics". Electrons always of themselves go from a warmer (higher energy level) to a cooler (lower energy level). That is, the initial elements in a burning process contain more energy than the products. Furthermore, the total amount of energy is constant. So, if products of combustion are less energy-rich than the burning elements, some energy must have "escaped" to the environment.
Let us look at an example of this. The simplest possible carbon-hydrogen molecule is the gas methane. This is composed of 4 hydrogen atoms and one carbon atom. In our model this is the reducing agent or "A". The oxidizing agent is oxygen or "B". If we stick a match or a spark into a mixture of methane and oxygen the former burns and we get water and carbon dioxide as products. In effect, the hydrogen atoms hop off the carbon in methane and bind to the oxygen atoms. The carbon also binds with oxygen giving us stable, low energy products.
We can look more closely and see what is really happening. As I mentioned above, the second electron shell is full when it contains 8 electrons. Now, atoms are friendly types and do not object to sharing electrons with other atoms. The "8-rule" simply states that a shell is full when it POSSESSES OR SHARES 8 electrons. When we add a little energy (the spark of burning match) to the oxygen-methane mixture, we provide enough energy to split the oxygen molecule (O2) into two oxygen atoms, each with only 6 electrons. By accepting 2 hydrogen atoms from methane, the oxygen once again fills its outer electron shell. The electrons from the hydrogen atoms in methane now reside in two water (H2O) molecules. The carbon joins up with 2 oxygen molecules forming CO2. All of the atoms in water and carbon dioxide now have or share 8 electrons in their outer shells and are "relaxed and happy" and quite unreactive. The energy "lost" to the environment can be seen and felt as light and heat from the flame.
The heat from burning material can be captured by heating water to steam as you can see in the picture of the old-fashioned locomotive. Remember, the real driving force here is the energy released when electrons hop from one atom to another. This is a form of "atomic energy", but not that we usually associate with this terminology.
A more modern example of release and capture of electron energy produced by combustion is shown in the next figure. Here, gasoline is burned in the cylinders of the car's motor, the heat expands the gas produced and forces the pistons downward. Again, the driving force here is "electron-hopping" from a carbon-hydrogen complex to oxygen, and the products are essentially CO2 and water.
What has all of this to do with you and me? The weight lifter here does not emit steam and has no mechanical motor. Can electron-hopping really be driving him too. Well, he does use oxygen and forms carbon dioxide from the food he eats.
Our "daily bread", be it vegetables, meat, milk, beer or anything else is largely comprised of carbon-based products. We "burn" these using oxygen from the atmosphere. In essence, we carry out the same combustion process that we use to produce steam or hot gases in our machines. The difference lies in the way we capture the released electron energy. In living organisms that energy is secured in a material we call ATP or adenosine triphosphate. All life is based on a process wherein the energy stored in ATP is released by splitting off a phosphate group from ATP and forming ADP or adenosine diphosphate and inorganic phosphate (Pi). We shall look closer at this soon but note here that our bodies are driven by capturing energy released from electron shells during combustion of carbon material as ATP. Atomic energy (read "electron energy") is the power that drives you, me, the dog and the tomato!
Just what is ATP? The next figure shows the detailed structure of this energy-rich compound. We can see that it contains a nitrogen base, adenine, a sugar, ribose and a chain of three phosphate groups. The phosphates are comprised of a central phosphorus atom and three oxygen atoms. The second and third phosphate groups are tightly grouped and interfere with one another. That is, the oxygen atoms repel each other quite energetically. And this means that they harbor energy and are rather unstable.
The terminal phosphate group can be split off from ATP forming ADP and inorganic phosphate. These are less energetic than the mother compound, ATP. The energy that is released in this process is used to drive the many diverse processes in all living organisms.
We can summarize this simply as shown in the next figure. The energy released by converting ATP to ADP and inorganic phosphate is used by our bodies to drive all of our various activities, both mental and physical. The real source here is the energy found in the carbon atoms in our food and electron-hopping from these to oxygen found in air. This combustion produces CO2 and water in the same manner as burning coal, gas and oil in ovens and machines. The difference here is that instead of using heat to increase pressure in a gas or water, we capture a good bit of energy in ATP. The total ATP concentration in most tissues is around 5 millimoles/kg and this is relatively constant. Even extreme exertion does not reduce ATP levels more than about 20%.
Here are some amazing facts about ATP:
1. There are about 50 grams of ATP in the adult human body. This covers approximately 5 minute's normal existence. We use about 40-60 kilograms of ATP daily. That means that our ATP stores must be replaced around 1000 times each day,
2. ATP is formed through oxidation of carbon atoms from sugars, starch, fat and proteins, that is, through electron migration from carbon to oxygen.
3. "Body energy" is equal to the speed of ATP synthesis.
4. ATP production is dependent upon good food, good circulation and lung function and good physical condition.
Electrons Can Capture and Store Energy; the Carbon Cycle.
Thus far, I have taken up use of energy released by electron movement from high to low energy states. However, it is quite clear that there must be a method to capture energy and renew our sources of high-energy electrons. The basic process here is movement of electrons back from a low energy state to a higher state. In other words, we have to be able to move "fallen" electrons back to orbitals or shells further from the atomic nucleus. And, in fact, this is an important and normal process. According to "Thermal Dynamics", electrons won't do this "of themselves"; they need an external source of energy. What we need then is a system to capture energy from an outer source, and this is found in green plants.
Green plants contain chlorophyll and this pigment has the ability to adsorb the energy of the sun. Plants couple this to photosynthesis, a process involving splitting of water back to oxygen and hydrogen and capturing the adsorbed energy as ATP. The ATP is utilized to drive reduction of CO2 with formation of new sugars and starch. Thus, plants create food for us from the waste products of our metabolism and, in the process, replace the oxygen we use to metabolize foods. Note that these synthetic processes are completely dependent upon solar energy. In the dark or during periods with limited growth, plants produce CO2 just as you and me.
In summary, almost all life on earth is completely dependent upon the solar energy trapped by green plants. They balance our carbon oxidation through reduction of the carbon dioxide we form and convert this to the food we eat. In the process, they also produce the oxygen we are completely dependent upon. This is the carbon cycle and is truly a wonder.
The Energy Content of Foods
The food we eat can be divided up into several classes; fats or lipids, sugars and starch, proteins and alcohols. These can give us energy, usually measured in calories per gram. It may be surprising for some of you, but these different foods contain varying amounts of energy. While fats yield 9 kilocalories / gram, sugars and starch give us a little less than half of this, that is, 4 kilocalories / gram. Proteins also give about 4 kilocalories / gram. Alcohol yields 7,5 kilocalories / gram. That means that a glass of wine gives us as much energy as double as much cola! Beer and wine are major contributors to the current global obesity epidemic.
What is the basis for these differences? Remember, the energy content of the food we eat is directly related to "electron-hopping" from hydrogen-carbon complexes to oxygen atoms. Food with many carbon-oxygen links can be said to be partially burned or oxidized before we eat it. It contains fewer high-energy electrons and, therefore, less energy.
Now, just look at the figure. You will quickly see that fats contain mostly carbon-hydrogen bonds and little oxygen. Fats or lipids are almost fully reduced and excellent donors of high-energy electrons. The sugar (glucose) at the bottom of the figure contains many oxygen atoms and is partially oxidized before being eaten. That means that it has fewer electrons to donate to oxygen during metabolism and, therefore, gives us less energy than fats. Alcohol (ethanol) lies between these in oxidation state and "energy content". It contains fewer hydrogen atoms and high-energy electrons per molecule than fats, but more than sugars.
We have Two Pathways of ATP Synthesis
I will remind my readers once again that ATP levels in all tissues are rather low, they are used rapidly, and are replaced just about as fast as they are draw upon. This close balance between synthesis and use is achieved by utilizing the energy released during oxidation of carbon compounds and movement of electrons from energy-rich shells to shells with a lower energy content. There is no other "form of magic" here. Once more, work includes all of our activities, both mental and physical.
Let us go to the next figure and see what kind of physiological reactions drive ATP synthesis.
We have two possible routes that produce ATP from ADP and inorganic phosphate in our bodies. The first is based on partial oxidation of sugars and is NOT directly dependent upon oxygen. We call this the anaerobic glycolytic pathway. Here, sugars are converted to lactic acid. We win two ATPs for each sugar molecule that goes through anaerobic metabolism. Again, this is "only burning" of the carbon atoms in a sugar. The product, lactic acid, still has "electron-energy" and can be further oxidized in the aerobic pathway.
Note that only sugars can be metabolized in this manner.
The metabolism of fats and proteins is locked to aerobic metabolism; that is, metabolism coupled to reduction of oxygen with formation of CO2 and water. Here, oxidation of lactic acid from anaerobic metabolism, fats and amino acids from digested proteins give a far greater ATP production from each carbon atom that is oxidized. We generally say that we win 32 ATPs for oxidation of six carbons in aerobic metabolism.
Now, that is a real difference! Why in the world do we use anaerobic metabolism at all? There are two main reasons for this.
1. Some of our body tissues just do not have the capability to run aerobic metabolism; notably blood cells.
2. Anaerobic metabolism is much faster than that oxygen-requiring aerobic pathway. We may not get much ATP for each carbon that is oxidized, but this is an extremely rapid process. Anaerobic metabolism may not be efficient and lactic acid does "hurt" when it builds up in our muscles, but anaerobic ATP production is high-speed.
Here is a table showing the differing rates of synthesis of ATP from various sources. I have not yet discussed phosphocreatine but can say that production of ATP from this high-energy intermediate is the most rapid of the ATP-producing systems in our bodies. We can set that rate to 100 so that we can compare the rate of synthesis of ATP from other substrates.
The next row shows the speed of ATP synthesis starting with sugar (blood glucose or sugar stored as glycogen) and proceeding through anaerobic metabolism to lactic acid. The rate is approximately one-half of that of synthesis from phosphocreatine.
The next two rows give you an idea about the rates of aerobic metabolism, first from sugar and then from fat. Aerobic sugar oxidation goes only half as fast as anaerobic metabolism. Fats go even slower since these must be released from adipose tissue, travel to muscles, and then be activated and finally oxidized.
We can willingly call up these processes when we need them. Remember, phosphocreatine is fastest, anaerobic sugar metabolism is fast but painful and exhausting, aerobic metabolism can continue for long periods but gives a relatively slow ATP synthesis.
Here is a good example of these processes.
The skiers who are lying and gasping came first over the finish line. That final sprint really took a lot of ATP and called for a major anaerobic sugar burning with lactic acid production, a fall in blood sugar levels and, at the same time, maximal aerobic metabolism. We can just let them lie there; they will be ok soon.
The fellow standing there came too late to the finish line; he could have sprinted even harder, used more ATP, activated anaerobic metabolism, become more pooped and possibly won the race.
Maybe those in the background are going on fat.
Muscle Composition Depends on Careful Selection of Parents!
Our muscles are made up of several fiber types. Type I is predominately aerobic and exhibits relatively slow contractions. Type IIB is mainly anaerobic has quick contractions. Type IIA has an intermediate contractile rate and metabolism. The composition of an individual's muscles is genetically determined and permanent. We can train up our bodies, improve circulation and breathing and build up muscle mass, but we cannot alter the types of fibers we have in our skeletal muscles. People with a predominance of those quick IIB fibers can excel in activities that demand explosive reaction, for example high-jumping, sprinting or weight-lifting. People with a dominance of slow aerobic fibers make excellent long-distance runners. You must choose your parents with care!
The figure shows sections of human muscles which have been stained to show which muscle types they are composed of. Quick anaerobic fibers are dark; slow aerobic fibers are light-colored. Here you can easily see that the high-jumper's leg musculature was dominated by quick anaerobic fibers. The marathon runner showed a dominance of slower aerobic fibers.
The muscles of a high-jumper had a relatively low oxygen uptake, stored a lot of sugar as glycogen, quickly produced lactic acid and exhibited rapid ATP synthesis over short periods.
The trained marathon runner had a relatively high oxygen uptake, a very well developed capillary system, marked aerobic fat metabolism and produced a lot of ATP over long time intervals.
A high-jumper or sprinter cannot compete in and expect to win long distance events. A slim marathon runner usually is no sprinter.
As a well-known Norwegian physiology professor used to say, "give me a muscle biopsy and I'll tell you which event you should train for".
Cellular Energy Reserves and Osmolarity
ATP is the immediate source of energy that drives our physiological functions. However, as I have explained, it is found in surprisingly small quantities in our tissues. Instead of storing ATP, we store substrates for oxidation which can quickly be mobilized and "burned" to CO2 and water. Once again, we utilize "electron energy" to drive our bodily functions. Why not just store ATP? Why must we go through that burning process to replace ATP?
Our tissues are made up of cells and these are bounded with a thin so-called plasma membrane. Salts and other water-soluble material can wander into our cells. In doing so, they cause water to follow. A host of mechanisms that I will not discuss here selectively pump excess material out of cells and tissues so that they maintain more-or-less constant physiological concentrations. Cells and tissues are held "iso-osmotic" with an osmotic pressure of about 300 milliosmoles / liter.
Let us look at a model showing what happens if cells are exposed to alterations in osmotic pressure. The figure shows red blood cells and their responses to increased and decreased osmotic pressure. The normal condition is shown in the center. Here you can see a balance in water flux in and out of the cells. They maintain a normal configuration. To the left you can see the result of removing salts and water from these cells. They collapse and cease to function. Equally destructive is an increase in cell volume caused by a salt and water influx as shown to the right. The arrow points to a cell ruptured by the increasing pressure and cellular expansion.
The point here is that we cannot store extra water-soluble material (for example ATP) as an energy reserve. Instead, nature has equipped us with two substrates for energy metabolism WHICH DO NOT DISTURB THE CELL'S OSMOTIC BALANCE. This follows two ingenious mechanisms:
1. We store sugars as a polymeric macromolecule, glycogen, which is not soluble. Instead, glycogen forms a surface in the cell's cytoplasm that adsorbs the enzymes essential for its metabolism. Thus, glycogen can release glucose when needed without altering the cell's osmotic pressure. This gives us a substrate for both anaerobic and aerobic energy metabolism. Glycogen metabolism is hormone-controlled and coupled to our energy needs. Glycogen stores are, however, somewhat limited. Driving anaerobic metabolism to its limits initiates uptake of sugar from the blood and, eventually, loss of consciousness.
2. We store carbon as fat. We all have fat-storing tissues, adipose tissue. Normal slim men store around seven kilograms of fat, women approximately 15 kilograms. The big advantage of these stores is that the fat lies outside of the cell's cytoplasm and is not water-soluble. Again, hormone steering controls fat metabolism such that fat is built up and broken down according to one's energy intake and expenditure.
I will point out once more, the energy we use to drive our body's functions comes from "burning" sugars, fats and proteins and by transferring electrons from these to oxygen. Electron-hopping from high to low energy states drives the system, also when we use our energy reserves, fat and glycogen.
Phosphocreatine, an Important Water-soluble Energy Reserve
Phosphocreatine is one of our most important energy reserves, especially in skeletal muscles. The figure shows its structure and route of synthesis. Phosphocreatine is made from ATP by transferring a high-energy phosphate from ATP to creatine. This allows us to "stockpile" energy, usually about two to three times the level of ATP in skeletal musculature. Thus, the concentration of ATP is around 5 millimoles/kilogram while the concentration of phosphocreatine lies between 18 and 20 millimoles/kilogram muscle.
How do muscles utilize phosphocreatine? Early work suggested that muscles might be able to use both ATP and phosphocreatine directly to fuel contraction. However, in the 1960s, Professor Robert Davies at the University of Pennsylvania clearly demonstrated that phosphocreatine is a "buffer" for ATP. Its high energy phosphate group must be transferred back to ATP before it can be utilized as an energy source.
We make approximately half of our body's creatine ourselves, the rest comes from food. The osmotic pressure from phosphocreatine is included in the normal pressure in our tissues. Once again, remember that our bodies carefully control the concentration of salts and other water-soluble materials in tissues such that this lies around 300 milliosmoles / kilogram.
Thus far, I have described ATP as a "high-energy" compound. Actually, it is better described as having an intermediate energy level. There are several normal high-energy intermediates in our metabolism that can transfer energy to ADP and Pi and induce formation of ATP. A good example of these is creatine phosphate. Creatine phosphate has a "free energy of hydrolysis" of -10.3 kcal / mole; ATP has a "free energy of hydrolysis" -7,5 kcal / mole. This means that energy can be transferred from creatine phosphate to ATP. More correctly, the energy-rich phosphate group of creatine phosphate can be transferred to ADP with formation of ATP and release of some heat. ATP can transfer its phosphate group to less energetic compounds, for example blood sugar or glucose, and form a sugar phosphate. Glucose phosphate has a "free energy of hydrolysis" of 3,3 kcal / mole. ATP has been described as the body's currency, serving to hand over energy from one agent to another. Furthermore, as Flanders and Swann so correctly pointed out, "energy can only of itself go from a "hotter" to a "cooler".
Why is phosphocreatine so important?
The answer is a question of timing. The next figure shows the sequential contribution of our four energy sources for muscle contraction. These curves give you an idea about the onset and duration of energy use from ATP (yellow curve), phosphocreatine (red curve), anaerobic metabolism of sugar (green curve) and aerobic metabolism of sugar, starch and fat (black curve).
Let us begin with ATP. Remember, ATP levels are relatively stable. A 20 % fall is huge! Direct utilization of ATP starts immediately at the beginning of muscle contraction but is balanced very quickly through use of phosphocreatine.
Phosphocreatine is a buffer for ATP. It balances out ATP consumption rapidly. BUT, note that the limited amount of phosphocreatine is used up within the first 60-90 seconds following initiation of muscle work. Anaerobic metabolism of sugar (glucose and glycogen) starts up and peaks just after this short period.
The importance of phosphocreatine lies in the fact that it bridges the delay between the end of the direct ATP-driven contractile period and the start of anaerobic sugar-driven ATP synthesis. This assures a constant energy supply during the first minutes of muscle activity.
Anaerobic sugar metabolism is a relatively ineffective and partial oxidation (burning if you will) but goes forward with great speed. Sprinters use anaerobic metabolism to run 100 meters. They do not even need to breath while running. The same explosive energy generation is used in weight lifting and hopping. The time span where this can function is limited. A maximal anaerobic exertion is limited to between two and three minutes.
Aerobic metabolism takes over after this period. Well-trained athletes with type I muscle fibers can run for several hours, using ATP generated by complete oxidation of sugars and fat through oxygen-linked processes. Keep in mind that anaerobic metabolism must be called upon for "sprints to finish" as seen in the picture of the ski competition. We can run relatively slowly for a long time using aerobic metabolism, but increasing speed requires the anaerobic use of glucose with formation of lactic acid.
Note that there is a sliding conversion from one source of energy to another, thus maintaining ATP formation and energy transfer at a more or less steady level during a work period.
How can I Feel Better and Increase Performance?
Let's first summarize all this business about energy.
1. The ultimate source of bioenergy (body energy if you will) is the energy of the electrons in the carbon and hydrogen atoms found in our food. This is made available through reaction with oxygen (oxidation or burning) leading finally to formation of carbon dioxide (CO2) and water. These products are reduced back to edible substances (food) by plants using solar energy. We have no other possibilities to obtain energy for our bodies.
2. We can oxidize carbon from food with or without direct use of oxygen. Anaerobic metabolism is quite rapid, and can provide energy for musculature for short and intense periods of activity. The partially oxidized sugar is converted to lactic acid which is then further oxidized later or in other tissues. Most organs cannot cover their energy requirements through anaerobic metabolism but must fully oxidize carbon to CO2 using oxygen and the aerobic pathway. Anaerobic metabolism can only use glucose or glycogen (a stored glucose polymer) as substrate and produces lactic acid. Much of the discomfort following intense activity is due to accumulation of lactic acid.
We can press our bodies to continue to make use of the anaerobic pathway after our glycogen reserves are exhausted. However, the carbon source in this situation is blood sugar which is the brain's normal source of energy. Since skeletal muscles make up 40-50 % of the body and the brain only about 1.5 %, the brain must lose in "competition" with muscles for the limited amount of blood sugar. So, extensive anaerobic metabolism in musculature reduces energy supplies to the brain with dizziness, temporary loss of sight (a so-called red-out) and eventually loss of consciousness as a result.
3. Aerobic metabolism can fuel the body over long time periods. It uses all possible substrates, especially lipids or fat. The aerobic pathway does not reduce blood sugar levels and interfere with the brain's metabolism. However, aerobic metabolism is rather slow and the muscular activity level supported is not equal to that of anaerobic metabolism. A sprint to finish activates anaerobic metabolism in addition to aerobic activity.
4. The secret to good performance is to maintain or increase the rate of formation of ATP. We can do this through:
a. Increasing storage of glucose as glycogen in the liver and in skeletal muscles. This is, in fact, done rather easily. The body guards itself against glycogen depletion by increasing stores if and when they are emptied. Muscle glycogen levels can be doubled for several days following a hard workout. Liver stores are also approximately doubled after the are used up. A hard workout several days before a competition gives us extra stored glucose when we meet for that contest. Empting liver glycogen by eating a low carbohydrate diet a few days before a game will increase liver glucose stores with ensuing improvement in the sugar reserves available to buffer blood sugar. You can click here for more information concerning glycogen storage.
b. Energy release from the oxidation of carbon atoms is dependent upon good blood circulation and good lung activity. Oxygen must come to our working tissues and CO2 must be removed. Physical training through daily activity is our best approach to good heart and lung function. I will take this up once more under the section about aging.
c. Humans can survive and live well on almost all natural diets, from the fat-rich Inuit diet, the protein-rich hunter diet and the carbohydrate-rich diet common under agriculture. There does not appear to be any special "secret diet" to make us perform "better". Good food, good daily exercise and a normal body weight (BMI* around 20-25) give a satisfactory start for physical activity. Athletes may have need to further develop their bodies but even here good normal diets are adequate.
* BMI = Weight (kg) / Height2 (meters)
d. We can train up aerobic musculature. The ATP-producing activity of individual muscle cells and the blood circulation around them is increased by physical training. Up to a point! Overtraining can, in fact, reduce muscle strength. The secret here for normal physical levels is daily activity.
"Tricks and Trash"; A few examples of false claims.
One "logical" conclusion from information about the effects of creatine might be that we should use creatine supplements to build up an energy reserve. A recent search of the Internet yielded more than 5,000.000 links to creatine. Creatine supplements comprise about 10 % (>$100,000,000 annually) of the sport-supplement market in the USA alone. One Internet link is shown in the figure.
Many studies of the effects of creatine on bodily function have been published. At best, a three percent increase in water content in muscles has been reported, though many reports claim much better performance and condition following creatine supplementation.
I have no doubt that taking a preparation that is "known" to improve performance will do just that. The question is whether this is just a placebo effect, that is a mental reaction to "help". That "knowing" may be just enough to help the body perform better.
Three things must be pointed out here.
1. We must not disturb the osmotic balance in our cells. We cannot increase the cellular content of water-soluble material without forcing water uptake, cellular swelling and eventual rupture. This does not occur since we have physiological mechanisms controlling uptake of water-soluble material and osmolarity. Excess water-soluble substances are excreted in urine. We cannot significantly increase the creatine and creatine phosphate levels in our tissues.
2. Creatine phosphate serves as a energy source within a small time-window, approximately 60-90 seconds after starting muscle work. There is no possibility for long-term effects.
3. Increased creatine intake leads to increased urinary creatine! A 90-fold increase has been reported. Creatine supplementation results in "very expensive urine".
We can look at another example of a dietary supplement, "known" to improve performance but, in reality, completely without physiological effects. The sugar ribose is supposed to build up energy and improve performance. In fact, we produce all the ribose we need from blood sugar.
Here are some clips from Internet advertisements.
Sugars taken orally go through the digestive tract and may be adsorbed in the small intestine. Specific transport systems for several sugars are found there. These work on only three materials: glucose, fructose and galactose. No other sugars normally found in food are taken up in the small intestine. Examples of sugars which are NOT taken up are sorbitol (used as a non-caloric sweetener), lactose (milk sugar which is not broken down in most adults), and ribose (which is supposed to increase strength and give extra energy). All of these are carried from the small intestine to the large gut where they are fermented by bacteria. The result is production of gas and great discomfort if the daily intake exceeds around 5-6 grams. These sugars are not a source of carbon atoms which can give energy when eaten!
A Norwegian weight-lifter, Stian Grimseth, used ribose under training for the Olympiad in Australia several years ago. He reported that he could indeed mark a loss of strength when he stopped taking ribose before the competition. He therefore continued eating the sugar during preparation for the Olympics. Unfortunately for him, a test in Australia clearly demonstrated that he had been using Nandrolone and he was disqualified and sent home. Grimseth strongly denied using the steroid preparation. However, analysis of the ribose product he had been using showed that it contained the steroid. His "good" experience with ribose followed a cynical steroid addition by the manufacturer; he was aided by Nandrolone, not ribose.
The picture is from a Norwegian newspaper which reported that he had sued the manufacturer of the ribose.
Aging, energy and performance
A sorry fact is that "sooner or later" we all find that we are just not as strong as we were earlier. Ski trails become steeper, diving flasks are heaver that they were years ago, stairs just are not as before...
The men in the picture were asked to run on a treadmill for one hour. The colors of the legs of the men in the following picture (from National Geographic) show how much aerobic and anaerobic metabolism they used during exercise. The blue color indicates aerobic metabolism, the yellow anaerobic tissues. Green is somewhere in between.
The fellow on the left (Keith) was 37 years old, weighed 135 pounds, body fat 5.3% of body weight. He exercised almost 2 hours daily. He had a maximal oxygen uptake (VO2) of 76 milliliters / minute. This is a complex measure and is dependent upon lung function, circulatory factors and uptake of the gas by exercising muscles. Note that main artery to his leg had a diameter of 12 millimeters. His daily exercise led to development of his aerobic capacity, the composition of his muscles and development of his circulation and pulmonary capacity. He had enough aerobic capacity to run without calling in partial oxidation and lactic acid formation.
Larry, the man in the middle, was 60 years old, weighed 165 pounds and had a body fat equal to 16.2 % of his weight. His VO2 was 41,9 milliliters / minute and he exercised 1 hour daily. His iliac artery had a diameter of 8 millimeters. His situation is rather typical for older men. In spite of daily training acts, his oxygen uptake capacity was far below that of the younger man. His circulatory capacity was also lower than Keith's as shown by his narrower iliac artery. While he did manage to run the required time on the treadmill, he had to use some anaerobic metabolism to supply the ATP needed. One could guess that he "felt" exercise more than Keith and limited his daily training accordingly.
Salvador (to the right) was 35 years of age and weighed 173 pounds. Thirty-five percent of his body weight was fat. He did not exercise daily. His iliac artery had a diameter of only 6 millimeters. He could not complete the the treadmill test but walked "to the finish". The strong yellow coloring in his leg indicates that, even though he only walked, he had to use anaerobic metabolism to provide energy. He certainly felt more pain during exercise than the two other men. This is typical for individuals who do not exercise and train up their aerobic musculature and circulation.
We see here the advantage of training to increase aerobic capacity and to reduce fatigue during exercise. Moreover, we can see that aging is accompanied by a reduction in the capacity for oxygen uptake and that reliance on anaerobic metabolism during work increases with age.
Once again, body energy is derived from the energy of electrons in the carbon and hydrogen atoms of our food. No pill or "magic" dietary supplement can replace this. Good food, good exercise and a sound life-style improves endurance at all ages.
Physical Condition and Health
I wish to show one more figure in this article. It is taken from an article in the New England Journal of Medicine published in 2002. The authors have examined the cause of death for many persons and arranged these according to the degree of training these persons had. The striking conclusion is that exercise and physical training does, in fact, protect us against death from most of the most common threats. Well-trained persons are less vulnerable to hypertension, pulmonary disease, diabetes, smoking, obesity and hyperlipemia than people with less or little training.
So, regardless of which energy supply you use, whether you are thick or thin, diabetic patient etcetera...
OUT AND EXERCISE. LIVE BETTER, HAVE MORE ENDURANCE, LIVE LONGER.