CSCS Study Guide Chapter 3: Bioenergetics

Edited by: Danielle Abel

Chapter 3 is all about how we use energy for movement. The chapter covers cellular respiration, including glycolysis, the Kreb's Cycle, & oxidative phosphorylation. Also, you will need to know the 2 different types of energy systems, the PCr cycle and Beta Oxidation. Lastly the book covers lactate, how it's produced and broken down in the body. 

Bioenergetics

Bioenergetics is how we make energy from food. Food is digested and becomes molecules that are then turned into energy (ATP). 

For example, if you eat avocado it is broken down into triglycerides, goes through lipolysis, and then beta oxidation. After this, it enter's the Kreb's cycle and goes through oxidative phosphorylation to form ATP. 

Whereas if you consume a donut it's broken down into glucose, then split into pyruvate and the pyruvate enters the Kreb's cycle and goes through oxidative phosphorylation to form ATP. 

ATP

ATP is short for adenosine triphosphate. It's a compound that consists of an adenosine molecule and 3 phosphates that is bound together by a high-energy bond. Breaking of the high energy bond results in energy, a hydrogen ion (metabolic acidosis), and ADP (adenosine diphosphate). 

Systems Contribute at Different Rates

You can't turn off energy systems, some are just contributing at greater or lesser rates. For example when you're sprinting for 10 seconds of less, the PCr Cycle is contributing the majority of energy to propel movement, however when you're running a marathon, fat is providing the majority of the energy for this ongoing movement. 

• PCr Cycle (aka Phosphagen System): Less than 10 seconds
• Anaerobic (fast) Glycolysis: 30 seconds - 2 minutes
• Aerobic Glycolysis: 2 minutes - several hours
• Fat: Very long duration (ex: ultra marathon)

Phosphagen System (PCr Cycle)

The phosphagen system is also referred to as the PCr Cycle and is also sometimes called the phosphocreatine system. The phosphagen system is used for efforts that involve 90-100% of max power, last 10 seconds or less, and require a large amount of rest between sets (ex: 1:12 to 1:20 work to rest ratio). 

Cellular Respiration

The easiest way to explain cellular respiration is to follow the path of a donut that you might eat. When the carbohydrate is broken down into it's smallest parts, you're left with glucose. Glucose can then enter the bloodstream (also known as blood sugar). Blood sugar can be stored as fat, glycogen, or used for energy. 

Glucose is a 6 carbon molecule, meaning it's made up of 6 carbon elements. 

Glycolysis

Glycolysis is just like it sounds, cutting glucose in half. Lysis means cutting or splitting and glyco means glucose. Glucose can be broken down under different conditions, anaerobic conditions (when no oxygen is present) and aerobic conditions (when oxygen is present). 

• Lactate is formed when glucose undergoes glycolysis anaerobically (also known as fast glycolysis) & occurs in the cytoplasm (in the cell but outside the nucleus/mitochondria of the cell)
• Pyruvate is formed when glucose undergoes glycolysis aerobically (also known as slow glycolysis)

Gluconeogenesis

Our bodies can also form new glucose from other compounds that are not carbohydrates. For example, we can make glucose from:

• Lactate
• Amino Acids
• Glycerol

Lactic Acid vs. Lactate

Something that many people get confused by is whether or not lactate is what causes lactic acid, but that is not the case. As we discussed earlier, hydrogen ions are produced when the high energy bond in ATP is broken down. Hydrogen is acidic, so as we're breaking down glucose into ATP (under anaerobic conditions), yes, we're making lactate, but it's not the lactate itself that causes lactic acidosis and the burning feeling from intense exercise, it's actually the hydrogen ion accumulation. 

Lactate & Lactate Threshold

Lactate is formed when glucose is broken down under anaerobic (no oxygen) conditions. The muscle fibers (cells) that are mostly responsible for lactate production are primarily our Type 2x and 2a fibers. If the production of lactate exceeds the clearance, lactate will accumulate. Keep in mind lactate is oxidized by Type 1 muscle fibers and by the heart. 

The lactate threshold is where we can no longer clear lactate without it accumulating, when this happens we switch to anaerobic energy production or fast glycolysis. In untrained people the lactate threshold is around 50-60% of max oxygen uptake, however in trained people it is typically 70-80% of max oxygen update. 

Onset of blood lactate accumulation or OBLA causes intermediate and large motor units to be recruited (Type 2x and Type 2a). Additionally, catecholamines are released to increase blood glucose. Training near the lactate threshold or onset of blood accumulation allows you to work at higher intensities without as much fatigue. 

Aerobic Glycolysis & The Kreb's Cycle

During aerobic glycolysis glucose is broken down to form pyruvate which gives you ATP. 

The Kreb's Cycle occurs in the mitochondria (nucleus) of the cell and it's a process that requires oxygen. Pyruvate loses a carbon molecule and becomes Acetyl CoA (2 carbons). This cycle generates 2 ATP. 

Oxidative Phosphorylation

Like the name implies, oxidative phosphorylation is oxidative, meaning oxygen must be present and it occurs in the mitochondria of the cell. This process is the last step in cellular respiration and produces 34 ATP in total. 

When you combine aerobic glycolysis, the Kreb's Cycle, and oxidative phosphorylation, you get a net of 38 ATP in total. 

Beta Oxidation

Again, we see the word oxidation, so oxygen must be present. Beta oxidation also occurs in the mitochondria of the cell. When we think about "fat burning," keep in mind that fat cells are called adipocytes and adipocytes contain triglycerides which can then be broken down into Acetyl CoA and can then enter the Kreb's Cycle (which is also oxidative). 

Excess Post Exercise Oxygen Consumption

EPOC is simply excess post exercise oxygen consumption. If you accumulate an oxygen debt or deficit during exercise, you will need to "pay it back" after the workout; this is EPOC. High-intensity training has higher EPOC (up to 15% extra calorie burn). For example, if you burned 500 calories in a workout (keep in mind you can't measure this with a fitness tracker), you would burn an extra 75 calories as a result of EPOC. 

Training Program Design

A main reason why you need to know bioenergetics is to design a program that promotes the goals of your athlete or client. Considerations that you need to think about that directly relate to bioenergetics include the level of intensity and the duration of the session. 

Support & Courses Available

Ready for more support to help you prep for the CSCS exam? Join our Facebook Group, “Strength and Conditioning Study Group,” here. Ready for even more? Our 24-module CSCS Prep Course has bioenergetics completely laid out for you with even more content than what we’ve provided here, plus chapter quizzes to help you pass the NSCA exam; click the link here to check it out.