Muscle and Exercise Physiology

Jerzy A. Zoladz

• Publisher: Academic Press
• Year: 2018
• ISBN:
  9780128145944
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

Muscle and Exercise Physiology is a comprehensive reference covering muscle and exercise physiology, from basic science to advanced knowledge, including muscle power generating capabilities, muscle energetics, fatigue, aging and the cardio-respiratory system in exercise performance. Topics presented include the clinical importance of body responses to physical exercise, including its impact on oxygen species production, body immune system, lipid and carbohydrate metabolism, cardiac energetics and its functional reserves, and the health-related effects of physical activity and inactivity. Novel topics like critical power, ROS and muscle, and heart muscle physiology are explored.

This book is ideal for researchers and scientists interested in muscle and exercise physiology, as well as students in the biological sciences, including medicine, human movements and sport sciences.

• Contains basic and state-of-the-art knowledge on the most important issues of muscle and exercise physiology, including muscle and body adaptation to physical training, the impact of aging and physical activity/inactivity
• Provides both the basic and advanced knowledge required to understand mechanisms that limit physical capacity in both untrained people and top class athletes
• Covers advanced content on muscle power generating capabilities, muscle energetics, fatigue and aging

Section II

Muscle Energetics and Its Performance

Outline

• Chapter 5 Muscle Energetics
• Chapter 6 Efficiency of Skeletal Muscle
• Chapter 7 Muscle Function
• Chapter 8 Critical Power
• Chapter 9 Energy Cost of Human Locomotion on Land and in Water

Chapter 5

Muscle Energetics

Graham J. Kemp, Department of Musculoskeletal Biology and Liverpool Magnetic Resonance Imaging Centre (LiMRIC), University of Liverpool, Liverpool, United Kingdom

Abstract

This chapter summarizes the main processes by which metabolic energy is mobilized to support mechanical work in skeletal muscle. The focus is on processes on the seconds-to-minutes timescale which can be measured noninvasively in vivo by techniques such as magnetic resonance spectroscopy (MRS), yielding quantitative information about cellular metabolism in vivo difficult to obtain in any other way. Muscle energy metabolism can be simplified to a system of ATP supply (oxidative and by anaerobic glycolysis) and demand, buffered by the creatine kinase (CK) reaction. There are important relationships between ATP turnover and cellular pH homeostasis: glycolytic production of lactate is accompanied 1:1 by H⁺, both of which can leave the cell via specialised membrane transporters. ³¹P MRS in particular gives access to some key parts of this system. However, interpretation must take account of the technical characteristics of the methods and their relationship to the underlying biochemistry and physiology.

Keywords

Metabolism; ATP turnover; bioenergetics; pH; glycogenolysis; mitochondria; noninvasive methods; 31 P magnetic resonance spectroscopy; skeletal muscle

Acknowledgments

Kemp’s recent work in this area has been supported by the Biotechnology and Biological Sciences Research Council UK (BB/I001174/1) and by the Medical Research Council UK and Arthritis Research UK (MR/K006312/1) as part of the MRC—Arthritis Research UK Centre for Integrated Research into Musculoskeletal Ageing (CIMA).

5.1 Introduction

Skeletal muscle is primarily a mechanism for using metabolic energy to do mechanical work. A useful way to think about this is to consider the integrated processes which generate and use ATP: ATP production includes the classical biochemical pathways of glycolysis, the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation; ATP usage is dominated by the myosin ATPase which generates muscular force. This chapter describes the main features of how ATP production is matched to ATP use during relatively short-term periods of exercise, concentrating on aspects which are accessible to noninvasive analysis in vivo using the techniques of magnetic resonance spectroscopy (MRS), particularly phosphorus magnetic resonance spectroscopy (³¹P MRS).

5.2 The Basic Metabolism and Physiology of Skeletal Muscle Energetics

Fig. 5.1 summarizes the basic outline of muscle energy metabolism, which will be required to underpin our account of how this can be assessed and measured in vivo.

Figure 5.1 The basic outline of muscle energy metabolism and how it can be studied in vivo See main text for details. Muscle is simplified to a system of ATP supply and demand, buffered by the creatine kinase (CK) reaction which equilibrates phosphocreatine (PCr), creatine (Cr), ATP, ADP, and H⁺. ADP and inorganic phosphate (Pi) are 1:1 stoichiometric products of ATP hydrolysis, and also substrates for ATP synthesis by anaerobic glycolysis and oxidative metabolism. The resting muscle spectrum on the right illustrates which parts of the system are accessible to phosphorus magnetic resonance spectroscopy (³¹P MRS). Also shown diagrammatically are the direct measurement of muscle lactate by proton magnetic resonance spectroscopy (¹H MRS), and the indirect measurement of muscle O₂ content by the non-MR technique of near infrared spectroscopy (NIRS). Lactate, O₂ and H⁺ fluxes across the muscle cell membrane (not shown) are directly accessible by the invasive technique of arteriovenous difference (AVD) measurement. All muscle metabolites are, in principle, accessible by the invasive technique of muscle biopsy.

5.2.1 ATP Turnover

For present purposes we can simplify muscle to a system of ATP supply and demand, buffered by the creatine kinase (CK) reaction. The CK reaction equilibrates phosphocreatine (PCr), creatine (Cr), ATP, ADP, and H⁺. ADP and inorganic phosphate (Pi) are 1:1 stoichiometric products of ATP hydrolysis, and also substrates for ATP synthesis by anaerobic and oxidative means. In skeletal muscle in the situations we are concerned with here, anaerobic glycolysis is predominantly from muscle glycogen, and oxidative metabolism is predominantly the oxidation of acetyl coenzyme A derived from glycolysis via pyruvate dehydrogenase, followed by oxidative phosphorylation mediated by the mitochondrial electron transport chain and cytochrome oxidase.

An important consequence of ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• List of Contributors
• Preface
• Section I: Skeletal Muscle Morphology
• Section II: Muscle Energetics and Its Performance
• Section III: Muscle Metabolism and Exercise Physiology
• Section IV: Body Adaptation to Exercise
• Section V: Heart Muscle and Exercise
• Index