The Physiology of Physical Training

Zsolt Radák

• Publisher: Academic Press
• Year: 2018
• ISBN:
  9780128151389
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

The Physiology of Physical Training provides complete coverage of the physiological and methodological aspects of physical training, providing essential knowledge for anyone involved in exercise physiology. Physiological processes at the cellular level (and for the whole organism) are covered to better explain particular training methods and convey a deeper knowledge and understanding of training techniques. Coverage of exercise training-induced adaptive responses and the most appropriate training methods to bring about targeted adaptive changes are also included. This is the perfect reference for researchers of physiology/kinesiology and human kinetics, practicing coaches, graduate students and sports medicine specialists.

• Describes exercise-induced adaptation, from the cell to the whole body
• Demonstrates practical applications of exercise for injury, disease prevention and improved physical performance
• Fully integrates the knowledge of molecular exercise physiology and training methods

Chapter 1

Basic Cellular Functions, Cellular Adaptation, and Metabolism

Abstract

The cell is the basic unit of all living organisms containing cell organelles and limited by its cell membrane. In higher developed organisms, cells are specialized and cooperate with each other to a great extent. The success in evolutionary selection depends on the viable information of DNA and the ability of the cells to adapt to environmental factors.

Keywords

Cellular adaptation; Metabolism; Organisms; DNA; Cell; Organelles

The cell is the basic unit of all living organisms containing cell organelles and limited by its cell membrane. In higher developed organisms, cells are specialized and cooperate with each other to a great extent. The success in evolutionary selection depends on the viable information of DNA and the ability of the cells to adapt to environmental factors.

The discovery of DNA and decoding of its information was one of the greatest discoveries in the 20th century, and lets us explore and further understand the functions of the human body, heredity of phenotypical traits, and mechanisms of diseases; we can also use decoded genetic information to determine the role of genetic variations in sport performance and competences. Knowledge of genetic factors in sport performance is a basic requirement in individual sport selection. In this chapter, we address cellular functions since a thorough knowledge of basic cell biology is essential to understand more complex physiological and methodological processes and functions, which enable us to influence these processes to our advantage within limits.

1.1 Cell and Organelles

Cell cytoplasm is surrounded by a cell membrane; in the case of a muscle cell or fibers, this is called sarcolemma. The cell membrane is composed of a double layer of phospholipid molecules which are partly hydrophobic facing inside and partly hydrophilic facing outside. Embedded within this membrane is a variety of protein molecules that act as channels and pumps, transport proteins that move different molecules into and out of the cell, and structural proteins. Membrane receptors are specified according to their structure and function. For example, growth factor receptors, after binding to their hormone, initiate a process that stimulates protein synthesis, which results in an increase in size in the case of a muscle. Insulin receptor activation leads to the translocation of GLUT4 transport protein to the cell membrane, which allows the uptake of sugar molecules from the blood by the musculature.

One of the most important roles of cell membrane is its involvement in the transport processes of the cell, which can be active (not requiring energy) or passive (driven by a concentration gradient). A concentration gradient is required for the stimulation of a cell. This gradient is maintained by pumps; a Na-K pump works against the ion gradient by using the energy of ATP molecules, and pumps out Na⁺-ions and pumps in K⁺-ions. Inside the cell in the cytoplasm, there are several organelles, which are in close association with the membrane (Fig. 1.1).

Fig. 1.1 Cell basic structure. A simplified graphic show the basic cell components and organelles.

The endoplasmic reticulum (EPR) plays an important role in cell protein and lipid transport, and in protein synthesis in conjunction with ribosomes, which are associated to the cell’s membrane. EPR in muscle is known as sarcoplasmic reticulum, which functions as Ca⁺⁺ ion storage. In response to stimulation, Ca⁺⁺ ions flood the sarcoplasm, and upon binding to troponin they allow the formation of actomyosin complex, resulting in muscle contraction.

Active reuptake of Ca⁺⁺ ion to the sarcoplasmic reticulum is required for muscle relaxation, which is catalyzed by a Ca⁺⁺-ATPase enzyme. Thus, Ca⁺⁺ ions are necessary for muscle contraction; however, a high intracellular Ca⁺⁺ concentration inhibits muscle relaxation, causing contracture.

DNA is located in the nuclear chromatin organized by histone proteins, which protect the integrity of the genetic information. DNA is vulnerable because of its huge size (uncoiled length 1.7–8.5 cm), so it is crucial to preserve its structure against mechanical and chemical impacts. Nuclear DNA encodes genetic information using 3 billion nucleotides (Fig. 1.2).

Fig. 1.2 A chromosome. Nuclear DNA stores genetic information specific to individuals, which are encoded by nucleotide base pairs.

DNA is organized into chromosomes, and an organism’s complete set of DNA is called a genome. In the nucleus of every human somatic cell there are 46 chromosomes (made up of 23 pairs), which in turn contain 50 × 10⁶–250 × 10⁹ base pairs, which are compressed in a 1.9 μm area in a compact structure.

The capacity of human DNA would allow the encoding of 3 million average size proteins; however, only a portion of the whole DNA encodes proteins. A gene is a region (locus) in DNA that encodes information of proteins in the form of base pairs. The main function of the genome is to store the information for gene transcription and consequential protein expression. Upon stimulation of the cell (e.g., hormone-ligand binding in a cell membrane), gene transcription may be initiated, leading to mRNA synthesis and consequential protein synthesis (e.g., motor proteins in skeletal muscle). It is worth noting that 90% of DNA does not encode proteins, and the function of the silent parts is not fully understood, nor its influence on the remaining 10%.

DNA contains segments called pseudogenes, similar to genes, but its transcription does not lead to protein synthesis, or even inhibit it. The functions of pseudogenes are not yet well understood; however, their number and variations show differences in a higher volume in individuals and also between species than those present in genes. Therefore further examination of pseudogenes may have a more profound effect than the study of genes in sport performance and individual sport selection in the future.

DNA can be found in mitochondria as well. Mitochondria have a size of 0.5–12 μm, and are surrounded by a double membrane. Mitochondrial DNA (mtDNA) encodes proteins of oxidative phosphorylation, and other proteins of mitochondria are synthesized in the nucleus and transported to the mitochondria. In the inner membrane, electrons generated from nutrients flow through the electron transport chain, and are translocated to molecular oxygen resulting in H₂O molecules, and energy in the form of ATP used by cells (Fig. 1.3).

Fig. 1.3 Mitochondrial electron transport chain. Electron transport chain in the inner membrane of mitochondria comprises five protein complexes. Complex I pumps out protons to the space between the inner and outer membrane of the mitochondria using NADH as an energy source, and transfers electrons to Complex III. Complex II is a parallel electron transfer pathway to Complex I transferring electrons from FADH2 to Complex III, but unlike Complex I, no protons are transported to the intermembrane space. Complex III transfers electrons to Complex IV and pumps four protons per electron. Complex IV pumps two protons into the intermembrane space before electrons are transferred to molecular oxygen, leading to the production of the final metabolite, H₂O. Complex V is an ATP synthase, which acts as an ion channel that provides for a proton flux back into the mitochondrial matrix. This reflux releases energy, which is used to drive ATP synthesis.

Skeletal muscle and cardiac muscle contain large amounts of mitochondria in the proximity of myofibrils, by which most of the ATP is metabolized. Mitochondrial membranes mainly influence the characteristics of these cell components. Most of the mitochondrial enzymes are located inside the mitochondria, in the matrix. These enzymes play a role in pyruvate, lipid, and Krebs-cycle (see later). The complexes embedded in the inner membrane produce the ATP from pyruvate, which is derived from glycolysis or lipid oxidation. Lipid metabolism is more efficient compared to carbohydrates since lipids contain six times more energy than the same amount of glycogen. All the glycogen stored in the cells can be burned in 1 day, whereas lipid storage is able to provide energy for a month. Thus, mitochondria play an important role in energy-producing processes and ATP production (Fig. 1.4).

Fig. 1.4 Mitochondria. Mitochondria are an ATP-producing unit of the organism, and also play a role in programmed cell death and adaptation following physical training.

In skeletal muscle, subsarcolemmal (below the membrane) and intermyofibrillar (close proximity to myofibrils) mitochondria are distinguished based more on their locations in the cell and less on their function. The number of mitochondria can be elevated significantly by physical training. This will be addressed in detail in Chapter 2.

Another important organelle of the cell is lysosome containing digestive enzymes, which break down proteins. These enzymes play a role in balancing the metabolism and catabolism of proteins. This balance is an important part of cellular homeostasis.

1.2 Cellular Adaptation

Upon stimulation, the cell responds to the stimulus with changes in protein synthesis. On the cell surface there are many sensors embedded in the membrane. Upon stimulation, two types of responses are possible. If a stimulus is extremely strong, and the cell cannot maintain its function, it induces a signal, which leads to the synthesis of proteins involved in programmed cell death, called apoptosis. This process results in cell shrinkage...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• List of Figures and Tables
• About the Author
• Preface
• Acknowledgments
• Introduction
• Chapter 1: Basic Cellular Functions, Cellular Adaptation, and Metabolism
• Chapter 2: Skeletal Muscle, Function, and Muscle Fiber Types
• Chapter 3: Adaptation, Phenotypic Adaptation, Fatigue, and Overtraining
• Chapter 4: Fundamentals of Strength Training
• Chapter 5: Fundamentals of Endurance Training
• Chapter 6: Speed as a Complex Conditional Ability
• Chapter 7: Fundamentals of Joint Flexibility
• Chapter 8: Diet and Sport
• Chapter 9: Physical Training and Prevention
• Chapter 10: Physical Training and Aging
• Chapter 11: Sport Genetics
• Chapter 12: Physiology of Training Plan: Periodization
• Chapter 13: Testing
• Index