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Contents
Chapter Objectives:
- Know the basic terms we use for bioenergetics and metabolism as they relate to exercise and training.
- Discuss the central roles of ATP in muscular activity.
- Discuss basic energy systems that are present in the body and their ability to supply energy for various activities.
- Discuss training effects on the bioenergetics of skeletal muscle.
- Know the substrates each energy system uses and discuss substrate pattern use with different activities.
- Make training programs that show understanding for human bioenergetics and metabolism, especially the metabolic specificity of training.
Essential Terminology
Bioenergetics is the flow of energy in a biological system. This is mainly referring to the conversion of food to energy we can use. Food is made up of carbs, protein, and fats.
Catabolism is the process of breaking large molecules down into smaller ones. For example, we break down carbs into glucose.
The opposite process of catabolism is anabolism. This is the building up process.
ATP is energy that is obtained from catabolic reactions used to drive the anabolic ones through intermediate molecules. Without ATP we would not be able to do any muscular activity or grow our muscles.
Energy Systems
We have three different energy systems that we use in our body. These are the phosphagen system, Glycolysis, and the oxidative system.
The Phosphagen System
This system provides the energy we use for the short term, high-intensity type activities. Even if you are doing low-intensity work, this system comes into play at first. So, it is present at the start of all exercise but very vital to high-intensity short work like a play in football or maybe even a sprint.
ATP stores
We do not store enough ATP in the body for all exercise. We really only store a small amount.
ATP is the main energy source for all basic cell functions.
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Creatine kinase is the main thing used in the phosphagen system. It is used to maintain the right concentration of ATP in the muscles. In the phosphagen system, we reproduce ATP very quickly.
Control of the Phosphagen system
The Law of Mass Action says that the reactant concentrations or products within a solution drive the direction of the reaction that will occur.
Glycolysis
Glycolysis is basically defined as breaking down carbs into glycogen within the muscles or glucose within the blood. And this is to resynthesize ATP.
The end result of glycolysis is pyruvate, which will follow one of two potential paths..
- Pyruvate may convert to lactate
- Pyruvate may move to the mitochondria
Glycolysis and the formation of lactate.
We form lactate from the pyruvate due to an enzyme known as hydrogenase.
This doesn’t yet result in lactic acid though.
Lactate also isn’t the result of fatigue.
Glucose + 2Pi + 2ADP → 2Lactate + 2ATP + H2O
Lactate will be converted by the body into glucose when it moves to the liver
We call this process the Cori Cycle.
Glycolysis and the Krebs Cycle
Acetyl-CoA is the substance that pyruvate is converted to when it gets into the mitochondria.
Acetyl Co-A will enter the Krebs Cycle.
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The NADH molecules will enter the electron transport system, or ETC, and will be used to synthesize ATP again.
Glucose + 2Pi + 2ADP + 2NAD+ → 2Pyruvate + 2ATP + 2NADH + 2H2O
The Energy Yields for Glycolysis
When we are using glycolysis, we have one blood glucose molecule yielding a net two ATP molecules.
Control of Glycolysis
The process of Glycolysis is started with high concentrations of both ADP, P, and ammonia. There also is a decrease in the pH levels and AMP.
Glycolysis may be inhibited by low pH, CP, Citrate, ATP, and free fatty acids.
The Lactate Threshold and The Onset of Blood Lactate
Lactate thresholds , LTs, represent increasing reliances on the anaerobic mechanisms.
Lactate threshold is also a marker for the Anaerobic Threshold.
The lactate threshold is seen as the moment of exercise intensity where the concentration of blood lactate starts increasing well above the baseline concentration it usually has.
The Lactate threshold starts around 50 – 60% of the max oxygen uptake, or VO2 max, in people who are not well trained.
Trained athletes typically have the threshold starting when they reach 70 – 80%.
The onset of the blood lactate is second in the rate of the body’s lactate accumulation.
The lactate threshold really only occurs at these high intensities of exercise.
The Oxidative System (Aerobic System)
The oxidative system serves as the primary source of ATP for our bodies during longer and lower intensity activities.
This oxidative system uses fats and carbs as substrates to make ATP.
Glucose and Glycogen Oxidation
The metabolism of muscle glycogen and glucose in the blood starts with glycolysis and ends with the Krebs Cycle.
Fat Oxidation
Triglycerides will be broken down by the hormone-sensitive hormones. This breakdown will then release free fatty acids into our bloodstream. These free fatty acids circulate in the blood and enter the muscle fibers when needed.
The free fatty acids will next enter the mitochondria after they have entered the muscle fiber. In the mitochondria, they will be broken down more to form the Acetyl CoA and hydrogen protons used in other energy systems.
Protein Oxidation
Protein is not a main source of energy for the body. This is because it serves other more important purposes and is more of a last resort
The Proteins are broken down into amino acids and then those amino acids are made into glucose, pyruvate, and the many other things that we need to do the Krebs cycle and end up making ATP.
Metabolic Specificity of Training
Using the right intensities and rest intervals will permit the selection and use of specific energy systems while training for specific goals.
Oxygen Uptake and the Aerobic and Anaerobic Contributions to Exercise
Oxygen uptake is a measure of someone’s ability to take in and use oxygen. The higher someone’s uptake, the more fit they are thought to be.
The anaerobic Contribution to total energy cost of exercise is known as oxygen debt. Following exercise, the uptake of oxygen stays above the preexercise levels for some time that will vary depending upon intensities and duration of work.
Postexercise oxygen uptake is known as oxygen debt, or also EPOC (excess postexercise oxygen consumption.
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Tyler Read
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