Blood lactate accumulation and muscle deoxygenation during incremental exercise

Area of Science:

• Exercise Physiology
• Sports Science
• Biomedical Engineering

Background:

• Understanding blood lactate concentration ([La](b)) increases during submaximal exercise is crucial but controversial.
• Near-infrared spectroscopy (NIRS) offers a non-invasive method to study muscle oxygenation.
• Previous research suggests varying physiological responses at different exercise intensities.

Purpose of the Study:

• To investigate the relationship between muscle deoxygenation and blood lactate accumulation during incremental exercise using NIRS.
• To determine if NIRS can identify the onset of blood lactate accumulation.

Main Methods:

• Five well-trained mountain climbers performed incremental cycle ergometer exercise.
• Measurements included pulmonary gas exchange, earlobe [La](b), and muscle oxygenation (Delta[O(2)Hb], Delta[HHb]) via NIRS.
• The "point of inflection" for [La](b) was identified, alongside changes in total hemoglobin and oxygenation index.

Main Results:

• Total muscle hemoglobin increased up to 60-65% of peak oxygen consumption (VO(2 peak)), then plateaued.
• The oxygenation index showed an accelerated decrease from 60-65% VO(2 peak), indicating muscle deoxygenation.
• The onset of muscle deoxygenation strongly correlated with the point of inflection for blood lactate accumulation (r(2) = 0.95).

Conclusions:

• NIRS can detect muscle deoxygenation that coincides with the onset of blood lactate accumulation during exercise.
• This muscle deoxygenation is likely due to capillary-venular hemoglobin desaturation, possibly influenced by lactic acidosis.
• NIRS provides valuable insights into the physiological mechanisms underlying exercise intensity and lactate production.