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Determining the Contribution of the Energy Systems During Exercise
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Blood lactate accumulation decreases during the slow component of oxygen uptake without a decrease in muscular

J M O'Connell1, J M Weir1, B R MacIntosh2

  • 1Faculty of Kinesiology, Human Performance Laboratory, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1N4, Canada.

Pflugers Archiv : European Journal of Physiology
|May 28, 2017
PubMed
Summary
This summary is machine-generated.

The slow component of pulmonary oxygen uptake during heavy exercise is linked to decreasing anaerobic metabolism, not increasing energy cost from muscle inefficiency. This suggests a shift towards aerobic energy supply over time.

Keywords:
Anaerobic energyExercise metabolismHeavy exerciseOxygen uptake kineticsSevere exercise

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Area of Science:

  • Exercise Physiology
  • Metabolic Responses to Exercise
  • Skeletal Muscle Metabolism

Background:

  • The slow component of pulmonary oxygen uptake ([Formula: see text]) during prolonged exercise above the lactate threshold is traditionally attributed to increased energy demands from inefficient muscle contractions.
  • This phenomenon is often assumed to be coupled with sustained anaerobic metabolism, indicated by rising blood lactate levels.

Purpose of the Study:

  • To investigate the relationship between the slow component of pulmonary oxygen uptake ([Formula: see text]) and blood lactate accumulation during sustained heavy exercise.
  • To test the hypothesis that increased [Formula: see text] is accompanied by constant or increasing blood lactate levels, signifying sustained anaerobic metabolism.

Main Methods:

  • Ten male subjects completed 9 minutes of cycle ergometry at a power output 60% above their lactate threshold.
  • Pulmonary oxygen uptake ([Formula: see text]) and blood lactate concentrations were measured throughout the exercise duration.
  • Energy contribution from aerobic and anaerobic sources was calculated based on [Formula: see text] and lactate accumulation.

Main Results:

  • Blood lactate accumulation decreased over time, indicating a diminishing anaerobic contribution to energy production.
  • The aerobic contribution ([Formula: see text]) to total energy supply increased progressively throughout the 9 minutes of exercise.
  • Total energy cost remained relatively stable after 3 minutes, with minor increases attributed to ventilatory muscle work.

Conclusions:

  • The slow component of pulmonary oxygen uptake ([Formula: see text]) during heavy exercise is associated with a *decreasing* anaerobic energy contribution beyond 3 minutes.
  • This finding challenges the traditional view that the slow component is driven by increasing inefficiency and sustained anaerobic metabolism.
  • The results suggest a shift towards a more efficient aerobic energy provision as exercise duration increases, even with a rising [Formula: see text].