Prior heavy exercise eliminates VO2 slow component and reduces efficiency during submaximal exercise in humans

Area of Science:

• Exercise Physiology
• Human Physiology
• Sports Science

Background:

• The pulmonary oxygen uptake (VO2) slow component is a phenomenon observed during sustained moderate-intensity exercise.
• Its relationship with muscle metabolic changes, particularly lactate accumulation and acidosis, remains a subject of investigation.

Purpose of the Study:

• To test the hypothesis that the VO2 slow component is linked to increasing muscle lactate.
• To determine if prior heavy exercise (PHE) with acidosis affects VO2 kinetics and exercise efficiency.

Main Methods:

• Nine subjects performed 10-minute cycling bouts at 75% of peak VO2, before (CON) and after (AC) PHE.
• Continuous breath-by-breath VO2 measurements and muscle biopsies were taken.
• Muscle lactate, acetylcarnitine (ACn), and phosphocreatine (PCr) concentrations were analyzed.

Main Results:

• Muscle lactate was higher during AC but stable during CON exercise.
• PHE eliminated the VO2 slow component and reduced gross exercise efficiency during AC.
• Initial VO2 kinetics were unaffected by PHE, despite increased ACn and reduced PCr.

Conclusions:

• The VO2 slow component is not explained by progressive acidosis, as lactate levels remained stable during CON.
• Reduced gross efficiency during AC and the VO2 slow component may stem from impaired muscle contractility and additional motor unit recruitment.
• PHE's effects on VO2 kinetics might be influenced by residual fatigue.