Aerobically generated CO(2) stored during early exercise

Area of Science:

• Exercise Physiology
• Human Metabolism
• Respiratory Physiology

Background:

• Muscle metabolic alkalosis occurs during early exercise, linked to phosphocreatine hydrolysis.
• Femoral vein blood pH, K+, and HCO3- increase without elevated PCO2, indicating CO2 conversion to HCO3- rather than pulmonary elimination.
• Understanding early CO2 store dynamics is crucial for exercise physiology.

Purpose of the Study:

• To quantify the increase in early exercise CO2 stores.
• To determine the specific contribution of exercise-induced metabolic alkalosis (E-I Alk) to these CO2 stores.
• To investigate the relationship between CO2 kinetics and oxygen uptake during exercise.

Main Methods:

• Measurements of CO2 stores were conducted at work rates below the lactic acidosis threshold (LAT) to isolate the E-I Alk effect.
• The transient increase in CO2 stores was monitored from the airway, starting around 15 seconds into exercise.
• Analysis included components from the Haldane effect, increased tissue PCO2, and E-I Alk.

Main Results:

• CO2 stores increased significantly within 15 seconds of exercise onset, peaking around 60 seconds and normalizing by 3 minutes.
• The E-I Alk component constituted a major portion of the increased CO2 stores, averaging 61% at 60% LAT and 68% at 80% LAT.
• The kinetics of O2 uptake correlated with CO2 store changes, and the O2 deficit correlated with the E-I Alk component.

Conclusions:

• A significant portion of the aerobically generated increase in CO2 stores during early exercise is attributed to bicarbonate (HCO3-) produced from phosphocreatine breakdown.
• Exercise-induced metabolic alkalosis plays a key role in transient CO2 buffering and storage.
• These findings enhance our understanding of immediate metabolic and respiratory responses to exercise.