At the onset of constant-load submaximal exercise,
ventilation increases rapidly, followed by a slower rise
toward a steady-state value. Arterial PO2 and PCO2 are
maintained relatively constant during this type of
exercise.
During prolonged exercise in a hot/humid environment,
ventilation “drifts” upward due to the influence of rising
body temperature on the respiratory control center.
Incremental exercise results in a linear increase in VE up
to approximately 50% to 70% of O2 max; at higher work
rates, ventilation begins to rise exponentially. This
ventilatory inflection point has been called the ventilatory
threshold.