1. Chapter 11 Acid-Base Balance During Exercise
EXERCISE PHYSIOLOGY
Theory and Application to Fitness and Performance, 6th edition
Scott K. Powers & Edward T. Howley

2. Acids, Bases, and pH Acid Molecule that can liberate H+ ions
Raises H+ concentration
Lactic acid
Base
Molecule that is capable of combining with H+ ions
Lowers H+ concentration
Bicarbonate pH
Measure of H+ ion concentration
pH = -log10[H+]

3. pH of Blood Normal Acidosis Alkalosis
Abnormal pH can disrupt normal body function and affect performance

4. The pH Scale
Figure 11.1

5. Acidosis and Alkalosis
Figure 11.2

6. Sources of H+ Ions During Exercise
Volatile acids
Carbon dioxide
Fixed acids
Sulfuric acid
Phosphoric acid
Organic acids
Lactic acid
CO2 + H2O  H2CO3  H+ + HCO3-

7. Sources of Hydrogen Ions Due to Metabolic Processes
Figure 11.3

8. Sport and Muscle Acid-Base Balance
Risk of Acid-Base
Sport Disturbance
Baseball Low
Basketball Low-to-moderate
Boxing Low-to-moderate
Cross-country skiing Low
Football (American) Low
100-meter sprint Low
100-meter swim Low
400-meter run High
800-meter run High
1,500-meter run Moderate-to-high
5,000-meter run Moderate
10,000-meter run Low-to-moderate
Marathon run Low
Soccer Low-to-moderate
Weight lifting (low repetitions) Low
Volleyball Low
Table 11.1

9. Importance of Acid-Base Regulation During Exercise
Failure to maintain acid-base balance may impair performance
Inhibit ATP production
Interfere with muscle contraction
Acid-base balance maintained by buffers
Release H+ ions when pH is high
Accept H+ ions when pH is low

10. Acid-Base Buffer Systems
Intracellular
Proteins
Phosphate groups
Bicarbonate
Extracellular
Hemoglobin
Blood proteins
Bicarbonate buffering system
CO2 + H2O  H2CO3  H+ + HCO3-

11. Acid-Base Buffer Systems
Buffer System Constituents Actions
Bicarbonate Sodium bicarbonate Converts strong acid
system (NaHCO3) into weak acid
Carbonic acid Converts strong
(H2CO3) base into weak base
Phosphate Sodium phosphate Converts strong acid
system (Na2HPO-4) into weak acid
Protein system COO- group of a Accepts hydrogens in the
molecule presence of excess
acid
NH3 group of a Accepts hydrogens in the
Table 11.2

12. Regulation of Acid-Base Balance
Lungs
When H+ concentration increases (low pH)
Increases ventilation
CO2 is “blown off” and pH increases
Kidneys
Regulate blood bicarbonate concentration
Important in long-term acid-base balance
Not significant in acid-base balance during exercise

13. Regulation of Acid-Base Balance During Exercise
Lactic acid production depends on:
Exercise intensity
Amount of muscle mass involved
Duration of exercise
Blood pH
Declines with increasing intensity exercise
Muscle pH
Declines more dramatically than blood pH
Muscle has lower buffering capacity

14. Changes in Arterial Blood and Muscle pH During Exercise
Figure 11.4

15. Regulation of Acid-Base Balance During Exercise
Buffering of lactic acid in the muscle
60% through intracellular proteins
20–30% by muscle bicarbonate
10–20% from intracellular phosphate groups
Buffering of lactic acid in the blood
Bicarbonate is major buffer
Increases in lactic acid accompanied by decreases in bicarbonate and blood pH
Hemoglobin and blood proteins play minor role

16. Changes in Blood Lactic Acid, HCO3-, and pH During Exercise
Figure 11.5

17. Regulation of Acid-Base Balance During Exercise
First line
Cellular buffers
Proteins, bicarbonate, and phosphate groups
Blood buffers
Bicarbonate, hemoglobin, and proteins
Second line
Respiratory compensation
Increased ventilation in response to increased H+ concentration

18. Lines of Defense Against pH Change During Intense Exercise
Figure 11.6