Chapter 11: Acid-Base Balance during Exercise

OBJECTIVES

By studying this chapter, you should be able to do the following:

1. Define the terms acid, base, and pH.

2. Discuss the principal ways that hydrogen ions are produced during exercise.

3. Discuss the importance of acid-base regulation to exercise performance.

4. List the principal intracellular and extracellular buffers.

5. Explain the role of respiration in the regulation of acid-base status during exercise.

6. Outline the interaction between intracellular/ extracellular buffers and the respiratory system in acid-base regulation during exercise.

OUTLINE

• Acids, Bases, and pH 257

• Hydrogen Ion Production during Exercise 258

• Importance of Acid-Base Regulation during Exercise 260

• Acid-Base Buffer Systems 260

  • Intracellular Buffers 260

  • Influence of Muscle Fiber Type and Exercise Training on Intracellular Buffer Capacity 261

• Extracellular Buffers 261

• Respiratory Influence on Acid-Base Balance 262

• Regulation of Acid-Base Balance via the Kidneys 264

• Regulation of Acid-Base Balance during Exercise 265

KEY TERMS

acid

acidosis

alkalosis

base

buffer

hydrogen ion

ion

pH

respiratory compensation

strong acids

strong bases

INTRODUCTION

An ion is any atom that is missing electrons or has gained electrons. A hydrogen ion is formed by the loss of the electron; molecules that release hydrogen ions are called acids. Substances that readily combine with hydrogen ions are termed bases. In physiology, the concentration of hydrogen ions in body fluids is expressed in pH units. The pH of body fluids must be regulated (i.e., normal arterial blood pH = 7.40 ±.02) in order to maintain homeostasis. This regulation of the pH of body fluids is important because changes in hydrogen ion concentrations can alter the rates of enzyme-controlled metabolic reactions and modify numerous other normal body functions. Therefore, acid-base balance is primarily concerned with the regulation of hydrogen ion concentrations. High-intensity exercise can present a serious challenge to hydrogen ion control systems due to hydrogen ion production, and hydrogen ions may limit performance in some types of intense activities (7, 14, 16, 20, 40). Therefore, given the potential detrimental influence of hydrogen ion accumulation on exercise performance, it is important to have an understanding of acid-base regulation.

ACIDS, BASES, AND pH

In biological systems, one of the simplest but most important ions is the hydrogen ion. The concentration of hydrogen ions influences the rates of chemical reactions, the shape and function of enzymes as well as other cellular proteins, and the integrity of the cell itself (10, 46).

An acid is defined as a molecule that releases hydrogen ions and thus can raise the hydrogen ion concentration of a solution above that of pure water. In ...