CSCS Study Guide Chapter 3: Bioenergetics of Exercise and Training

Chapter 3 of the Essentials of Strength Training and Conditioning answers the following; How many energy systems are active at once? What two things dictate which energy system the body primarily uses during exercise?

Chapter 3 of Essentials of Strength Training and Conditioning focuses on Bioenergetics of exercise and training. In plain language the chapter is about how your body converts energy into fuel that can be used for exercise. It is also about what causes exercise to cease and training specific energy systems.

Some fuel sources are able to provide more energy than others.

Key Items:

  • Know how much ATP is produced from oxidation of one glucose molecule via different pathways.
  • Know the time intervals and intensity associated with different energy systems.
  • Know how work to rest intervals produce a varied training effect.

Bioenergetics of Exercise and Training

  • Metabolic Specificity - Training try to try and produce results in a specific energy system.

Essential Terminology

  • Bioenergetics - flow of energy.
  • Energy - fuel that can be converted into different forms. Carbs, fats, and proteins for example.
  • Catabolism - the breakdown of large molecules into smaller molecules.
  • Anabolism - the construction of large molecules from smaller molecules.
  • Exergonic Reactions - reactions that release energy.
  • Endergonic Reactions - reactions that need energy.
  • Metabolism - the sum of all the reactions in the body. Energy balance.
  • Adenosine Triphosphate (ATP) - the main form of energy your body uses to do work. Exercise is not possible without it. One adenine and three phosphates.
  • Hydrolysis - the breakdown of one molecule of ATP.
  • Adenosine Triphosphatase (ATPase) - the specific enzyme that breaks down ATP.
  • Myosin ATPase - the specific enzyme that breaks down ATP for cross bridge recycling.
  • Calcium ATPase - the specific enzyme that breaks down ATP for pumping calcium into muscle.
  • Sodium-Potassium ATPase - the specific enzyme that breaks down ATP for releasing sodium to maintain the right balance in muscle after depolarization.
  • Adenosine Diphosphate - after one phosphate is lost from ATP. One adenine and two phosphates.
  • Inorganic Phosphate - a free phosphate.
  • Adenosine Monophosphate (AMP) - the result of releasing a phosphate from ADP. One adenine and one phosphate.
  • The body stores limited amounts of ATP so more must be produced in order for activities to continue.

Biological Energy Systems

  • The three basic energy systems that produce ATP in mammals are the Phosphagen system, the Glycolitic system and the Oxidative system.
  • Anaerobic - energy processes that do not require oxygen.
  • Aerobic - energy processes that require oxygen.
  • Phosphagen System - anaerobic process. Occurs in muscle sarcoplasm. Short-term, high intensity.
  • Glycolytic System - anaerobic. Occurs in muscle sarcoplasm.
  • Krebs Cycle - the electron transport system.
  • Oxidative System - aerobic process. Occurs in mitochondria of muscle cells. Primary source of ATP at rest.
  • Mitochondria - cells power plant.
  • Only carbohydrates can be broken down for energy without oxygen.
  • All energy systems are at play at any given time. The one that is emphasized the most depends on first intensity and second duration.
  • Creatine Phosphate (CP) - a high energy molecule like ATP. Small amounts so not as much energy as ATP.
  • Phosphocreatine (PCr) - another word for Creatine Phosphate.
  • Creatine Kinase - the enzyme that accelerates the creation of ATP from CP and ADP.
  • Type II muscle fibers store more CP than type I.
  • Adenylate Kinase Reaction - another reaction important for replenishing ATP.
  • Myokinase - another term for the Adenylate Kinase reaction.
  • Glycolysis - the breakdown of carbohydrate from either muscle or glucose from the blood.
  • Law of Mass Action - the concentrations of reactants will drive the reactions.
  • Mass Action Effect - another term for law of mass action.
  • Near-Equilibrium Reactions - reactions that move in a direction based on the law of mass action.
  • Glycolysis has more steps in energy conversion than the phosphagen system so it cannot produce as quickly but, it can produce a lot more energy because there is a lot more glucose and glycogen than CP in the body.
  • Pyruvate - the product of glycolysis. It can be turned into lactate or moved into the mitochondria.
  • Lactate - one of the two forms of energy that can be produced from pyruvate.
  • Anaerobic Glycolysis - when pyruvate is converted into lactate.
  • Fast Glycolysis - another term for anaerobic glycolysis.
  • Aerobic Glycolysis - when pyruvate is moved into mitochondria. It involves more steps so it’s called slow.
  • Slow Glycolysis­ - another term for aerobic glycolysis.
  • Glycolysis doesn’t depend on oxygen so anaerobic and aerobic are not good terms per se. The conversion depends on how fast the cell needs the energy.
  • Lactic Acid­ - often mistaken for the end product of glycolysis.
  • Lactate is not the reason why people have to cease exercise. H+ accumulation reduces the calls ph levels and slows down reactions. Lactate does the opposite, it consumes protons.
  • Metabolic Acidosis - an exercise induced reduction in cell ph levels. May be the cause of the peripheral fatigue that happens during exercise.
  • Energy Substrate - the energy that enzymes act on.
  • Gluconeogenesis - making glucose from non-carb sources.
  • Wet Muscle - muscle that has not been dried.
  • Cori Cycle - the cycle when lactate is transported by blood to the liver to be converted into glucose.
  • Lactate has been shown to return to pre-exercise levels about an hour after activity ceases and light activity can help with clearance rates.
  • Nicotinamide Adenine Dinucleotide (NADH) - a coenzyme, transported to mitochondria with pyruvate during glycolysis.
  • There are two primary ways to form ATP during metabolism, substrate-level phosphorylation and Oxidative phosphorylation.
  • Phosphorylation - adding an inorganic phosphate to another molecule.
  • Oxidative Phosphorylation - the formation of ATP via the Electron Transport Chain.
  • Electron Transport Chain (ETC) - a series of electron transporting compounds that transfer electrons from donors to acceptors.
  • Substrate-Level Phosphorylation - the direct resynthesis of ATP from ADP. Single reaction.
  • Phosphofructokinase [PFK] - an enzyme that speeds one of the synthesizing steps in glycolysis.
  • Glycogenolysis - the breakdown of muscle glycogen.
  • Allosteric regulation is when the product of a reaction feeds back to regulate the turnover rate of key enzymes in metabolic pathways.
  • Allosteric Inhibition­ - when the product binds to the regulating enzyme and the reaction feeds back and slows the turnover rate.
  • Allosteric Activation - when the product binds to the regulating enzyme and the reaction feeds back and speeds the turnover rate.
  • Rate-limiting Step - the step that limits the reactions speed.
  • Lactate Threshold (LT) - the point where blood lactate begins to suddenly rise above baseline.
  • Oxygen Uptake - the consumption of oxygen.
  • Onset of Blood Lactate Accumulation (OBLA) - a second increase in the rate that lactate begins to rise in the blood. May represent when higher motor units begin to be recruited.
  • Flavin Adenine Dinucleotide (FADH2) - a redox cofactor, something that gives and accepts electrons.
  • Cytochromes - electron carriers.
  • Oxidative phosphorylation is the pathway where cells combine enzymes with oxygen to produce ATP. The text says this is responsible for over 90% of ATP production.
  • Beta Oxidation - reactions where free fatty acids are broken down creating acetyl-CoA and hydrogen protons. The end of this process can create hundreds of ATP molecules.
  • Protein oxidation also provides energy but, not a significant amount short term. Long term it may contribute 3-18% in prolonged activity.
  • Branched-Chain Amino Acids - three amino acids, leucine, isoleucine and valine.
  • Slow-glycolysis substrate phosphorylation creates 4 molecules of ATP.
  • Slow-glycolysis oxidative phosphorylation creates 6 molecules of ATP.
  • Krebs cycle substrate phosphorylation creates 2 molecules of ATP.
  • Krebs cycle oxidative phosphorylation creates 24 molecules of ATP.
  • Krebs cycle GTP creates 4 molecules of ATP.
  • Glycolysis consumes 2 ATP if starting with blood glucose. May be 4 depending on the transport system used to move NADH to the mitochondria.
  • In general, as intensity increases then duration is shortened.
  • An energy systems rate of production and capacity usually have an inverse relationship.
  • 0-6 second activities are usually extremely high intensity and fueled mainly by the phosphagen system.
  • 6-30 second activities are usually very high intensity and fueled mainly by the phosphagen and fast glycolysis system.
  • 30 second-2 minute activities are usually high intensity and fueled mainly by fast glycolysis.
  • 2-3 minute activities are usually moderate intensity and fueled mainly by fast glycolysis and the oxidative system.
  • Activities that take longer than 3 minutes are usually low intensity and fueled mainly by the oxidative system.
  • At no time does one energy system provide all the energy for an activity.

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Substrate Depletion and Repletion

  • Depletion - using up.
  • Repletion - making, replenishing.
  • The ceasing of activity may have to do with phosphagen depletion. They say that stores should be replenished 8 minutes after exercise.
  • Liver glycogen is important during low intensity exercise.
  • Above 60% intensity, muscle glycogen becomes important.
  • Repletion of muscle glycogen is based mainly around post-exercise carb consumption. They say 0.7-3.0g per kg body weight is best.

Bioenergetic Limiting Factors in Exercise Performance

  • There are limiting factors to different kinds of activity and it is important to understand how this affects athletic events. Ex. Glycogen depletion can be a limiting factor in long aerobic activities.
  • It’s not known exactly what causes muscular fatigue but, limiting factors like ammonia accumulation and impaired calcium release have been shown to be factors.

Oxygen Uptake and the Aerobic and Anaerobic Contributions to Exercise

  • Oxygen consumption is a measure of how effective someone is at intaking, delivering and using oxygen during exercise.
  • Oxygen Deficit - making up for some of the energy that was supplied at the beginning of exercise via anaerobic mechanisms.
  • Oxygen Debt - post-exercise oxygen uptake.
  • Excess Post Exercise Oxygen Consumption (EPOC) - another term for Oxygen debt.
  • Oxygen deficit and post exercise consumption are not equal and have only been shown to be mildly related.
  • Oxygen debt depends on intensity, duration and the type of activity performed.

Metabolic Specificity of Training

  • Selecting the right intensity and rest can allow the “selection” of training specific energy systems.
  • Training in the wrong energy system can lead to less than ideal adaptations for specific sporting events and athletes.
  • Interval Training - a method of training that uses predetermined rest and work intervals of exercise and rest. Theoretically allows for more work at a higher intensity in less time than continuous training.
  • Work-to-rest Ratios - how much time you spend working and resting.
  • There is not a specific work-to-rest ratio that has been established as the best but it has been agreed that more work can be accomplished using intervals.
  • Re-synthesis rates are really important when determining work to rest ratios for different kinds of activity.
  • High-Intensity Interval Training (HIIT) - brief high-intensity exercise with short recovery periods.
  • Combination Training - cross-training anaerobic athletes in aerobic events. This however has been shown to limit anaerobic performance particularly for high-strength, high-power events.

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Steven Mack is founder and a Certified Strength and Conditioning Specialist at the private training studio, Simple Solutions Fitness. He consults for Stronger by Science, a leader in fitness research dissemination, and is a former Mizzou football walk-on. Steven dedicates his professional life to helping people through his writing, speaking, and role as a personal trainer.