Chapter 11 Acid-Base Balance During Exercise

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Chapter 11Acid-Base Balance During Exercise

• EXERCISE PHYSIOLOGY
• Theory and Application to Fitness and
  Performance, 6th edition
• Scott K. Powers Edward T. Howley

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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 -log10H
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pH of Blood

• Normal
• pH 7.40.05
• Acidosis
• pH lt 7.4
• Alkalosis
• pH gt 7.4
• Abnormal pH can disrupt normal body function and
  affect performance

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The pH Scale
Figure 11.1
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Acidosis and Alkalosis
Figure 11.2
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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-
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Sources of Hydrogen Ions Due to Metabolic
Processes
Figure 11.3
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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
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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

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Acid-Base Buffer Systems

• Intracellular
• Proteins
• Phosphate groups
• Bicarbonate
• Extracellular
• Bicarbonate
• Hemoglobin
• Blood proteins
• Bicarbonate buffering system

CO2 H2O ? H2CO3 ? H HCO3-
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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
• molecule presence of excess
• acid

Table 11.2
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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

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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

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Changes in Arterial Blood and Muscle pH During
Exercise
Figure 11.4
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Regulation of Acid-Base Balance During Exercise

• Buffering of lactic acid in the muscle
• 60 through intracellular proteins
• 2030 by muscle bicarbonate
• 1020 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

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

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Lines of Defense Against pH Change During Intense
Exercise
Figure 11.6