Introduction

During physical exercise, active muscles demand more oxygen, and the body adapts through multiple physiological mechanisms to ensure oxygen delivery matches metabolic needs. This article clarifies key statements about the oxygen supply changes to muscles during exercise, focusing on partial pressures of gases, temperature, pH, 2,3-biphosphoglycerate (2,3-BPG) levels, and hemoglobin affinity. It identifies incorrect statements to dispel common misunderstandings.

The Given Statements

• A. PO2 declines and PCO2 rises in active muscles

• B. Temperature increases and pH decreases in active muscles

• C. 2,3-biphosphoglycerate decreases in red blood cells and PO2 rises

• D. Metabolites accumulating in active muscles increase hemoglobin affinity for oxygen

Explanation of Statements

Statement A: PO2 Declines and PCO2 Rises in Active Muscles

• True.
  During exercise, active muscle cells consume oxygen rapidly for aerobic metabolism, causing a decrease in intracellular and interstitial PO2 (partial pressure of oxygen).
  Simultaneously, metabolic activity produces CO2 as a waste product, resulting in increased PCO2 in muscle tissue.

This gradient helps facilitate oxygen release from hemoglobin and enhances CO2 removal.

Statement B: Temperature Increases and pH Decreases in Active Muscles

• True.
  Muscle contractions generate heat, raising local temperature.
  Increased metabolism produces acidic metabolites (e.g., lactic acid), lowering pH in the microenvironment of active muscles.

Higher temperature and lower pH contribute to rightward shift of the oxygen-hemoglobin dissociation curve, aiding oxygen unloading to tissues.

Statement C: 2,3-Biphosphoglycerate Decreases in RBCs and PO2 Rises

• False.
  During exercise, 2,3-BPG levels typically increase or remain stable to reduce hemoglobin’s oxygen affinity, facilitating oxygen release.
  A decrease in 2,3-BPG would increase oxygen affinity, hindering oxygen flow to tissues.
  Also, PO2 in active muscles does not rise; it declines due to consumption.

Therefore, this statement contradicts physiological facts.

Statement D: Metabolites Accumulating in Active Muscles Increase Hemoglobin Affinity for Oxygen

• False.
  Metabolites like CO2, H+ ions, and lactic acid decrease hemoglobin’s affinity for oxygen, encouraging more oxygen release where it is needed.
  This is explained by the Bohr effect, where increased acidity and CO2 promote oxygen unloading.

Thus, accumulation of metabolites decreases rather than increases affinity.

Which Statements Are Incorrect?

• C and D are incorrect.

The Options

Physiological Summary of Exercise Effects on Oxygen Supply

Conclusion

The incorrect statements are:

• (4) C and D

Where:

• 2,3-BPG does not decrease during exercise to raise PO2;

• Metabolite accumulation does not increase hemoglobin oxygen affinity, it decreases it.