Pulmonary and leg VO2 during submaximal exercise: implications for muscular efficiency

Area of Science:

• Exercise Physiology
• Muscle Energetics
• Cardiopulmonary Function

Background:

• Muscle energetics during exercise are typically assessed via pulmonary gas exchange.
• This method assumes pulmonary oxygen uptake (VO2) changes accurately represent muscle VO2.
• The validity of this assumption across various exercise intensities needed direct investigation.

Purpose of the Study:

• To directly compare pulmonary and leg oxygen uptake (VO2) during cycling exercise.
• To determine if pulmonary VO2 accurately reflects muscle VO2 across a range of work rates.
• To validate the use of pulmonary gas exchange for calculating muscular efficiency.

Main Methods:

• Simultaneous measurements of pulmonary and leg VO2 were conducted during incremental cycle ergometry.
• Leg VO2 was calculated using blood flow (thermodilution) and arteriovenous O2 difference.
• Measurements were taken at work rates from 20-90% of maximum VO2, avoiding the VO2 slow component.

Main Results:

• The slope of pulmonary VO2 was not significantly different from the slope of leg VO2 (9.9 vs. 9.2 ml O2.W-1.min-1).
• Delta efficiency calculated from pulmonary VO2 (29.1%) was not significantly different from that calculated from leg VO2 (33.7%).
• These findings held true across a broad range of exercise intensities.

Conclusions:

• Pulmonary oxygen uptake (VO2) closely mirrors the VO2 changes occurring within exercising leg muscles.
• The metabolic cost of processes outside the exercising muscles remains relatively constant across exercise intensities.
• Pulmonary gas exchange measurements are a valid method for assessing muscle energetics and efficiency during exercise.