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Chapter Goals:
- Understand the energy systems and their roles in exercise.
- Know the roles of lactate as a buffer for acidity.
- Find the three main types of fatigue and their causes.
- Explain the relevance of carbs on performance.
Anaerobic Energy Systems
Bioenergetics describes the many processes of energy and macronutrient used in the body and relates to the function of many energy systems for the provision of fuel in exercise.
ATP
This is the only form of energy that the body can use for muscular contractions of any kind, and thus, it needs to be present for internally controlled actions.
This fuel source used for mechanical, chemical, and transport work all rely on the energy released from phosphate bonds stored in the ATP molecule.
We use enzymes to break the phosphagen bonds. Enzymes are protein components that are made by cells that function to catalyze a biochemical reaction.
Phosphagen Energy System
Phosphocreatine is stored inside cells for the quickest possible release of energy. Creatine is phosphorylated with inorganic phosphate ions for the formation of creatine phosphate.
Creatine phosphate is used by way of creatine kinase, which is an enzyme that catalyzes the phosphocreatine.
The basic sequence of creatine phosphate goes as such:
- Creatine phosphate is split into creatine and inorganic phosphate by the kinase, producing energy.
- The liberated phosphate uses the energy that was released to bind ADP and P to form ATP.
- The new ATP is then split into ADP and P, and energy is released.
This energy system is primarily used in high-intensity and quick sprint-like work.
This energy system is used up in only a few seconds, give or take. And it takes a total of 2 – 5 minutes to restore the entire energy storage of creatine phosphate.
Intermediate Energy – Glycolysis
As the need for energy increases, the phosphagen system loses its ability to keep up, and thus, the glycolysis system is started for the next section of time working out.
Glycolysis is the metabolic process that involves breaking down sugars through many reactions to provide ATP during anaerobic work.
Glucose is the basic form of sugar that is the main source of metabolism for the glycolytic system.
Glycogen is the stored form of carbs in the body, which is broken down to fuel mechanical work. It is mainly stored in the skeletal muscles and the liver.
While exercise continues at intense levels, ischemia happens as the excess levels of hydrogen build up, and this causes a drop in overall pH levels.
The results of ischemia are:
- Inhibition of enzyme reactions
- Alterations of calcium handling
- It may lead to intrinsic muscle fatigue
Ischemia is a low oxygen state resulting from obstructed arterial blood supply or inadequate blood flow, which leads to tissue hypoxia.
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Lactic acid and pyruvate are the molecules resulting from ATP usage in glycolysis.
Lactic acid is an energy substrate that is made as an end-product of glycolysis and many bodily tissues can use it as fuel for ongoing work. It serves to buffer hydrogen ions made by the metabolism of sugar.
Pyruvate is an energy substrate that results as an end-products of sugar metabolization in glycolysis while in the presence of oxygen.
When the body is in a scenario where it lacks glucose, it may go through the process of gluconeogenesis, which is the creation of new glucose molecules in the liver from other organic molecules like amino acids, pyruvate, lactate, and glycerol.
Energy System Transition
The usage of the energy systems comes in waves, as some are quicker than others, and the latter ones take time to get going.
The phosphagen system is present for the first 30 seconds, with its primary usage occurring in the first 10 – 15 seconds.
The anaerobic glycolysis system is reset and strong for around 3 minutes of time.
The aerobic oxidative system comes in as the main system for energy usage after the 3-minute mark for the glycolysis system.
The aerobic system is the metabolic pathway where the mitochondrion utilizes fats, pyruvate from carbohydrates, and amino acids from protein to produce ATP in the presence of oxygen.
A MET, or metabolic equivalent, measures the energy used and is expressed as multiples of the resting metabolic rate. One MET is the equivalent of 3.5 mL of Oxygen per kg of body weight per minute of work.
An anaerobic system is One of two major metabolic pathways, the ATP-PC phosphagen system or anaerobic glycolysis, that produces energy without the presence of oxygen.
The anaerobic systems provide the energy for high power, high-intensity activities.
A Steady-state is a condition within the body that indicates the current level of oxygen use matching demand.
EPOC, or excess post-exercise consumption, is a measurable increase in the rate of oxygen consumption after strenuous activity due to some deficit created by work.
EPOC is attributed to:
- Elevations in bodily temperature persisting post-exercise
- Ion leakage occurs across cell membranes, leading to a stronger reliance on active transport across the membrane for preserving homeostasis.
- Mitochondrial calcium uptake during exercise, reducing aerobic efficiency
- Increased levels of thermogenic hormones existing post-exercise
- The re-synthesis of glycogen in the liver from lactate
- The oxidation of the lactate in the mitochondria
Aerobic Metabolism
This is the making of ATP through paths that need oxygen, hence, the name aerobic.
Lipids are the main source of fuel for this energy system.
Lipids are various classes of organic molecules made up of fatty acids or their derivatives. The dietary sources include items like oils, fats, waxes, and cholesterol.
FatMax is a term used to describe the greatest intensity of work that can be done where fat is the main fuel source. We also refer to it as the aerobic limit.
The fat-burning zone is important to know, as this is a lower intensity zone of training where the main fuel source will be fats. This is generally considered to be around 65% of VO2 max or less.
Triglycerides are 90% of the fat the body will store as adipose tissue. They are made up of glycerol and three fatty acids that are bound together in a single molecule.
Free fatty acids are the liberated lipid molecules in our blood plasma and around the body’s remaining 10% of fat.
Lipolysis is the breakdown of triglycerides from storage form for the potential circulation for energy usage.
Anaerobic Work to Increase Aerobic Capacity
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- When the body has prolonged levels of energy demands, it may recruit assistance from the amino acids, which must be taken from protein sources in the body.
- This usually results in the proteins from the muscles being broken down and utilized, thus decreasing muscle mass to a small degree.
- This is not usually desired in athletic training.
Muscular Fatigue
We have far larger fat reserves in the body, so the ability to sustain long-duration lower-intensity exercise is easily seen.
Low-intensity exercise will be sustained largely by this metabolization of lipids, with some slight use of glycogen at times.
Higher or intermittent intensity work will rapidly deplete the body’s glycogen reserves.
It is usually considered to be around the one-hour mark when the depletion of most glycogen reserves is done. After that, the breakdown of bodily proteins may occur, and it becomes ideal for adding some sugars to the body during activity.
Recovery
Rapid fatigue occurs when we work at high intensities for short times, and when breaks are taken, we see the muscle attempt to return to the levels it had before starting the activity.
Delayed onset muscle soreness is a term we use to describe the severe muscle soreness expedited by inflammation as a response to damage to cells, ischemia, and tonic spasms. It is usually most present after 24 – 72 hours following intense training.
Cardiac Physiology
VO2 is the abbreviation for the body’s oxygen volume at any given time.
VO2 is the product of the oxygen pumped through the heart measured per minute; we call this cardiac output and the amount of oxygen used by the bodily cells at a given time, known as the A-Vo2 difference.
Cardiac output will be the total blood volume available for the bodily tissues, and the heart rate and stroke volume dictate it.
The Heart
The heart is the point that unites the cardiopulmonary and the cardiovascular systems together. It is divided into two sides, and both have their own tasks for their system.
The right side of the heart will receive the blood without oxygen from the working muscles and send it through the lungs to receive the oxygen.
The left side of the heart will receive this oxygen-rich blood from the lungs and pump it through the body to be used and returned.
Diastole is the heart’s relaxation phase, where the atrial chambers fill with blood.
Systole is the contraction phase where the blood is pumped out to the body.
Hemoglobin is the protein in red blood cells that helps transport oxygen to the tissues.
Cardiac Muscle Tissue
The cardiac muscle tissue is like the skeletal muscles, but it is involuntary, as we have no control over the beating of our own hearts.
The myocardium is the word for the heart’s specialized muscular tissue for the continuous contractions it needs.
Cardiac Output
This is calculated as the heart rate multiplied by the stroke volume.
Blood Pressure
This is the measure of the force or lateral pressure that the blood puts on the arterial walls. It is total peripheral resistance multiplied by cardiac output.
Vasodilation widens the vascular structures, which decreases blood pressure and allows more blood flow.
Hypertension is a condition where the blood pressure of someone is high. This negatively impacts the cardiovascular system due to the stress on the arterial walls.
Circulatory System
The arteries function to deliver large amounts of blood to the main body segments in the circulatory system.
Some factors that influence blood pressure during resistance training:
- The Valsalva maneuver
- Intra-abdominal pressure
- Compressive forces via our contractions
- Elevations in the CO
- Dehydration
- External compressive forces
Ventilation
In exercise, the rate of ventilation increases to meet the more active heart’s oxygen demand.
Chemoreceptors control ventilation during exercise bouts.
At the onset of exercise, body movements stimulate the brain to breathe quickly.
The Endocrine System
The endocrine system is a complex organ network that communicates to regulate the other body systems.
This effectively is the system that regulates the body to maintain the level of homeostasis in the system.
Hormones
All stress is going to cause a response in the form of hormones. This goes for both eustress and distress.
Eustress is a positive and desirable form of stress that influences physiological or psychological health.
Distress is the opposite. This is any negative form of stress that influences these two systems.
Hormones can be either steroids or polypeptides.
Steroid hormones are organic, cholesterol-based hormone compounds that serve many functions, like sexual development, reproduction, and metabolism.
Polypeptide hormones are chains of amino acids made in the ribosomes of the ER in endocrine cells.
Anabolic hormones are the compounds that work in tissue growth and building things in general.
Catabolic hormones will be the opposing ones, which focus on breaking stuff down.
Pituitary Hormones
The main hormones in this classification are the growth hormone, testosterone, and insulin-like growth factors.
Pancreatic Hormones
The pancreas has two main functions:
Producing the digestive enzymes for breaking down fat, carbs, and protein to absorb them via the small intestine lining
Regulating the blood sugar levels by use of insulin and glucagon
Thyroid Hormones
Thyroxine and tri-iodothyronine are the main managers of human metabolism.
Adrenal Hormones
Steroidal and neural hormones are produced in the adrenal glands.
The hormones produced here include aldosterone, corticosterone, cortisol, cortisone, estrogen, testosterone, epinephrine, norepinephrine, somatostatin, and substance P.
The fight-or-flight response comes into play with the adrenal hormones. This is found when stress is perceived, and the adrenal hormones increase their energy provisions and oxygen to the bodily tissues.
The endocrine glands to note are the anterior pituitary, thyroid, adrenal cortex, adrenal medulla, pancreas, liver, ovaries, and testes.
Resistance training causes many increases in hormones, as seen with growth hormones, thyroid hormones, IGF, cortisol, epinephrine, and testosterone.
Tyler Read
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