NCSF Personal Training Study Guide Chapter 4 – Human Physiology
NCSF Personal Training Study Guide Chapter 4 – Human Physiology 1

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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 looks to describe the many processes of energy and macronutrient use in the body and relates to the function of many energy systems for the provision of fuel in exercise.


    This is the only form of energy that the body can use for muscular contractions of any kind, and thus, it needed 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 of 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 both creatine and inorganic phosphate by the kinase, which produces 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 defined as the metabolic process which involves breaking down sugars through many reactions for the provision of 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 sored form of carbs in the body, which is broken down for the fueling of 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 that is a result of obstructed arterial blood supply or inadequate blood flow which leads to tissue hypoxia.

    Lactic acid and pyruvate are the two resulting molecules from ATP usage in glycolysis.

    Lactic acid is an energy substrate that is made as an end-product of glycolysis and it can be used by the many bodily tissues 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 end-products of sugar metabolization in glycolysis while in the presence of oxygen.

    When the body is in a scenario where it is lacking glucose, it may go through the process of gluconeogenesis, which is the creation of new glucose molecules in the liver from the 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 later 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.

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    The anaerobic glycolysis system is resent 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, is a measure of 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.

    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 that 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 a glycerol and three fatty acids that are bound together in a single molecule.

    Free fatty acids are the liberated lipid molecules found in our blood plasma and are around the remaining 10% of fat in the body.

    Lipolysis is the breakdown of triglycerides from storage form for the potential circulation for energy usage.

    Anaerobic Work to Increase Aerobic Capacity

    • 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 reserves of fats in the body, and as such, the ability to sustain the long-duration lower-intensity exercise is easily seen.

    Low-intensity exercise is going to be sustained largely by this metabolization of lipids, with some slight use of glycogen at times.

    Higher intensity, or intermittent intensity work, is going to result in rapid depletion of the reserves the body has for glycogen.

    It is usually considered to be around the one-hour mark where the depletion of the majority of the glycogen reserves is done. After that, breakdown of bodily proteins may occur, and it becomes ideal to add some sugars to the body during activity.


    Rapid fatigue occurs when we are working at high intensities for short times, and when breaks are taken, we see the muscle attempt to return to the levels it had prior to 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 used for the volume of oxygen the body uses 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 is going to be the total volume of blood available to be used for the bodily tissues, and it is dictated by the heart rate and the stroke volume.

    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 is going to receive the blood without oxygen from the working muscles and sent it through the lungs to receive the oxygen.

    The left side of the heart is going to receive this oxygen-rich blood from the lungs and pump it through the body to be used and return.

    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 within the red blood cells that helps with the transport of 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 heart.

    The myocardium is the word for the muscular tissue of the heart that is specialized 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 pressures that the blood puts on the arterial walls. It is total peripheral resistance multiplied by cardiac output.

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    Vasodilation is the widening of the vascular structures, which decreases blood pressure and allows for more blood to flow.

    Hypertension is a condition where the blood pressure of someone is high. This has negative impacts on 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 the blood pressure during resistance training:

    • The Valsalva maneuver
    • Intra-abdominal pressure
    • Compressive forces via our contractions
    • Elevations in the CO
    • Dehydration
    • External compressive forces


    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 network of organs that communicate for the regulation of the other body systems.

    This effectively is the system that regulates the body to maintain the level of homeostasis in the system.


    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 serves 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 the two main functions of:

    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 the human metabolism.

    Adrenal Hormones

    Steroidal and neural hormones are produced in the adrenal glands.

    The hormones produced here are things like 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 hormone, thyroid hormones, IGF, cortisol, epinephrine, and testosterone.

    NCSF Personal Training Study Guide Chapter 4 – Human Physiology 2
    NCSF Personal Training Study Guide Chapter 4 – Human Physiology 3
    NCSF Personal Training Study Guide Chapter 4 – Human Physiology 4

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