Metabolism and How Muscles Work
Metabolism
As athletes we all have some sort of training plan whether it is a causal workout routine to a highly structured and detailed plan. We all know that training will make us stronger and faster, but do you really know what is happening in your body when you train? In the following article I will give an overview of what is happening in our bodies during training. I’ll cover homeostasis, metabolism, and energy metabolism and I hope that you come away with a better understanding what is happening within our bodies during training.
Training
What happens during training? During training your body begins to learn to adapt to expected stresses that are brought about by physical activity. A change occurs at the cellular level which allows more energy to be released with less oxygen use. You start to develop more capillary pathways and your heart becomes stronger which both allow more oxygen and nutrients to be distributed in order to allow your body become more efficient. During training your muscles, tendons, and bones become stronger and adapt to become more proficient at performing specific activities. After you have become more efficient in training your body will start to shed unnecessary fat and your entire body becomes more efficient. Also, your resting heart rate and blood pressure will lower.
Energy
During our training routines I will take a safe guess that most of us find that we tend to start eating more. We need extra energy that goes along with the increase in activity that we are experiencing with training. This energy comes in the forms of: carbohydrates, proteins, and fats. Carbohydrates are sugars and starches that are used as fuel and to store energy. Proteins are complex molecules composed of amino acids. They are essential for growth, the building of new tissue, and the repair of broken-down tissue. Fats are compounds that store energy.
Every cell in our body requires energy and our body must have a way to convert the carbohydrates, proteins, and fats into energy. The method is called metabolism. Metabolism is constantly occurring within the trillions of cells in our body. Metabolism must be constantly regulated to insure a consistent internal environment no matter how the external or the body’s internal environment is changing. The process of monitoring and maintaining the body’s internal environment is called homeostasis.
Homeostasis
Homeostasis is defined as the process that maintains a constant internal body environment. It can be compared to the thermostat in your home. When it gets to cold inside your home, the thermostat kicks on the heat the house. When it gets too hot inside the thermostat kicks on the air conditioner. During exercise when we start to get hot we being to sweat. This is the body’s mechanism of cooing itself down. On the opposite extreme, when the body’s core temperature begins to drop we begin to involuntary shiver which generates heat.
Metabolism
In order to sustain life our body needs energy. It receives its energy from the breakdown of nutrients like glucose, amino acids and fatty acids. When we speak of metabolism we are only concerned with the chemical changes that occur within cell tissues. It does not include such things as digestion of food. During metabolism this breaking down is going on simultaneously as a building back up is happening; although they occur at different rates. These two acts that occur during metabolism are categorized into two phases: anabolism and catabolism. Anabolism is the building up of complex chemical compounds from simpler ones. Catabolism on the other hand is the breaking down of complex chemical compounds into simpler ones.
During anabolism there is a net result in new cellular material being made such as enzymes, proteins, cell membranes, new cells, and tissue growth. The energy that is produced is stored as glycogen and/or fat, and in muscle tissue. During catabolism (think of cannibalism) the complex biomolecules are broken down into simpler ones for energy production. It is the energy needed for the transmission of nerve impulses and muscle contraction.
Internally your body is constantly striving to seek a base rate of metabolism, or what is known as your metabolic set point. The metabolic set point is controlled by both your genetics and your environment. People with a slow metabolism tend to gain weight easily, whereas people with a high metabolism seem to not again weight no matter how much they eat. Exercise tends to keep the metabolic set point high, and more aerobic exercise tends the body to burn more fat for energy.
Your Diet and How it Affects Metabolism
The type of food we eat directly affects our metabolism. There are three things that can happen with the food we decide to eat: 1) It is burned as energy, 2) it is converted into body weight, and 3) it is excreted. All foods release heat when they are burned and this release is measured in kilocalories. A calorie is a unit of heat, but it is too small for study purposes and the kilocalorie is preferred.
Some of the foods we eat are not all burned completely to produce energy. Calories coming from proteins are used for the maintenance, repair, and growth of new tissues and organs. Calories that come from carbohydrates are used for energy. And calories from fat tend to be stored as fat in our bodies since they already have the same molecular structure as body fat.
The thermogenic effect is the measure of particular foods energy content and the tendency to be burned as heat. The higher a foods thermogenic effect the higher the heat production will be. This is directly correlated to an increase in oxygen consumption and an increase in metabolic rate. The more heat your body produces the more oxygen it needs. It is “food efficiency”, or a simple measure of how efficient a particular food is converted to body weight. High effect food tends to turn into body weight, while low efficient foods tend to burned as energy.
Good nutrition is about knowing what you are putting in your mouth to properly set up a fitness lifestyle (notice that I did not say the word “diet”. I do not believe in diets). By just looking at the calorie count for your food choices is not a proper way of setting up your nutritional program. You need to understand how your body will be using and burning those particular foods you choose to eat.
How Exercise Effects Metabolism
Metabolism is directly affected by exercise and is realized in your body’s anatomy, physiology, and biological makeup. Here are just some of the changes that are stimulated by endurance exercise: increase in muscle storage capacity, increase in resting ATP content, increase in mitochondria density, an increased in slow twitch muscle fibers, increase cardio output, and decreased body fat.
How drastic these changes are is a direct result of the type of exercise that you perform; either anaerobic or aerobic. The two main workouts are aerobic and anaerobic. High intensity workouts will create fast twitch muscles fiber development, while low intensity workouts will produce slow twitch muscle fiber development. Aerobic training is specific to greatly increasing your body’s functional capacity to transport oxygen and to burn fatty acids during exercise. Anaerobic training increases the body’s functional capacity for developing explosive strength and the maximization of short-term energy.
How Energy is Metabolized
Now that we have covered where energy comes from and how it affects metabolism, we will now discuss how that energy is metabolized. Energy metabolism is the chemical process that results in the breakdown of the carbohydrates, proteins, and fats by which energy is produced, used, and given off as heat. It is estimated that the body is 20% efficient at trapping this energy while the other 80% is given off as heat. This is why your body heats up quickly with physical activity.
Physical activities are classified into four groups: 1) Strength-Power, where energy comes from immediate ATP stores lasting about 0 to 3 seconds. 2) Sustained-Power, the energy comes from immediate ATP and CP stores, lasting about 0 to 10 seconds. 3) Anaerobic Power-Endurance, the energy comes from ATP, CP, and Lactic Acid, lasting about 1 to 2 minutes. 4) Aerobic-Endurance, the energy comes through the oxidative pathway, lasting over 2 minutes in duration. I will go over ATP, CP and the oxidative pathways shortly.
ATP – What is it and How is it Produced
ATP is Adenosine Triphosphate. It is the molecule that stores energy that can be used for muscle contractions. Anabolism and catabolism take place during the production of ATP. Energy production is focused on the rebuilding of ATP molecules once they are broken down and used for energy. When we are exercising our bodies require a constant supply of ATP for muscle contraction. Therefore, metabolic pathways must exist within our muscle cells with the ability to produce ATP rapidly. There are three methods that our muscles produce ATP: 1) ATP/CP Pathway, 2) Glycolytic Pathway, and/or 3) Oxidative Pathway. We will now take a look at each of these pathways. Learn more about ATP, or The Energy Pathways.
The ATP/CP Energy Pathway (first source)
ATP is the energy source for all human movement. The sad part is that our muscle cells only have a limited amount of ATP that is readily available for use. In an all out effort your ATP is gone in about 1.26 seconds. Whether you are doing and all out effort, or starting a slow workout, all activities start with the ATP/CP Pathway. For a short-term activity such as shotputting, this is enough energy. However, further use of your muscles will breakdown the ATP and it will lose one of the three phosphate molecules in order to release energy and then it becomes ADP (Ammonium Dihydrogen Phosphate). ADP can be resynthesized back into ATP with the help of CP (Creatine Phosphate) and an enzyme called cretine kinase. Just like ATP, CP is stored in small amounts and is falls rapidly after about 10 seconds of maximum effort. Within a minute your CP stores are completely depleted.
It is not clear through training if you can increase your resting level of ATP. What you should ask yourself though is “how quickly can ATP and CP stores be replenished?” And “can training help how quickly it will occur?” Current research indicates that ATP stores can be fully restored within about 3.5 minutes, while CP stores fully replenish in about 8 minutes.
The Glycolytic Pathway (second source)
The Glycolytic Pathway is anaerobic just like ATP/CP pathway. Once you breakdown the ATP/CP stores your body must break down carbohydrates to produce more ATP. This process either uses glucose or glycogen to convert ADP back into ATP. The resulting waste from this chemical process is lactic acid.
I think most of us have experienced the burn from lactic acid build up. Lactic acid starts to build more quickly than it can be flushed out of your muscle and results in muscular fatigue or “burn”. To stop this lactic acid build up and make the burn go away you have to slow down or stop. The lactic acid will then be converted to lactate which is either used as energy or to produce more glucose. This process is called gluconeogenesis. When muscles start to get fatigued it is rarely that the stored sugars are depleted, rather the limiting factor is the accumulation of lactic acid. Typically, the Glycolytic pathways maximum output is about 80 seconds before it is depleted. After this point the oxidative pathways take over.
How well your muscle can function in the Glycolytic pathway is determined by several factors such as: 1) How quickly you muscles can get rid of lactic acid. 2) What your pain threshold is for handling the pain of lactic acid burn. And 3) How far you can push back the effects of lactic acid pain until it becomes absolutely vital to get rid of the lactic acid. After about an hour after you stop your activity your blood lactate levels usually return to normal. Training can both increase your muscles ability to remove lactic acid and the onset of the anaerobic threshold. As for managing the pain, it must become something you embrace.
The Oxidative Pathway (third source)
Unlike the ATP/CP and Glycolytic pathways, the oxidative pathway uses oxygen to produce ATP. This pathway will produce more ATP than the other two, but it takes much longer. Pyruvate; which is produced through Glycolysis, undergoes oxidation to convert ADP back into ATP. It is in the oxidative pathway only that fat can be used as energy. The process for breaking down fat for energy is called beta oxidation. This is a very long process which does not directly produce ATP. While at rest about 70 percent of our energy comes from fat, not carbohydrates or proteins. As the intensity of your activity increases more carbohydrates are used instead of fat because beta oxidation can’t keep up.
Putting all Three Systems Together
Now that we are at information overload I will try to wrap up how all these systems interact and work with each other. It all starts with a signal coming from the brain asking for a muscle to contract. At this point the contraction requires a high energy molecule ATP (Adenosine Triphosphate). The immediate ATP store is released and broken down into ADP (Adenosine Diphosphate) within the first few seconds. The second immediate available cellular source is CP (Creatine Phosphate). There are more CP molecules than ATP molecules and they serve to instantaneously regenerate ATP molecules. The third energy system takes two ADP molecules and regenerates them into one ATP molecule and one AMP (Adenosine Monophosphate) molecule.
In Summary
We need energy to maintain our body’s chemical and physical activities. We get the energy our bodies need through carbohydrates, proteins, and fats. Our body is constantly striving to maintain a chemical balance known as homeostasis. Metabolism is the building up and breaking down of molecules in our body. Through metabolism the foods we eat are burned to liberate energy, converted in to bodyweight, or excreted.
ATP is the molecule that stores energy in a form that our used to contract our muscles. Our muscles can produce ATP by any one of the three metabolic pathways: ATP/CP, Glycolytic, or Oxidative. The formation of ATP without oxygen is called anaerobic metabolism and occurs in the ATP/CP and Glycolytic pathways. The formation of ATP with oxygen is called aerobic metabolism and occurs in the Oxidative pathway.
Glycogen is important for both anaerobic and aerobic activities. Strenuous exercise will rely on glycogen to power your muscles. In endurance exercise the primary fuel is fatty acids, but glycogen is still utilized.
