Ventilation and ventilatory thresholds
Minute ventilation, tidal volume and rate, first and second thresholds, VO2max.
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Minute ventilation: what is it?
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Air breathed per minute: tidal volume × breathing rate.
About 6 to 8 L/min at rest, over 100 in exercise.
During a test, VO2 stops rising while speed keeps increasing. What is measured?
- VO2max
- The first threshold
- Resting heart rate
- The respiratory quotient
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VO2max
The plateau marks maximal uptake.
First ventilatory threshold: what is it?
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The intensity where ventilation rises faster than VO2, close to the lactate threshold.
Talking is still possible.
Why does ventilation surge beyond the second threshold?
- Arterial blood runs short of oxygen and ventilation compensates
- It clears excess CO2 to buffer acidosis
- VO2 falls and ventilation takes over
- Lactate directly stimulates the breathing muscles
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It clears excess CO2 to buffer acidosis
Blowing off CO2 limits the fall in pH.