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

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+]

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

The pH Scale Figure 11.1

Acidosis and Alkalosis Figure 11.2

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-

Sources of Hydrogen Ions Due to Metabolic Processes Figure 11.3

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

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

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

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

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

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

Changes in Arterial Blood and Muscle pH During Exercise Figure 11.4

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

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

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

Lines of Defense Against pH Change During Intense Exercise Figure 11.6