The anaerobic threshold is the point during exercise when:
(1) there is a significant increase in the rate of lactic acid production
(2) there is an associated decrease in the bicarbonate concentration
(3) there is increased production of carbon dioxide with increased respiratory CO2 output
The anaerobic threshold correlates with a person's physical fitness.
Cycle ergometry is often used, with measurement of oxygen uptake, carbon dioxide production, end-tidal PO2, end-tidal PCO2, minute ventilation and other variables.
The V-slope method is performed on the plot of the oxygen uptake (VO2 in L per minute, as the x-axis) vs carbon dioxide production (VCO2 in L per minute, as the y-axis). The "V" comes from reference to the volumes of oxygen and carbon dioxide (page 2021).
2 lines are drawn:
(1) through the points of the early exercise period
(2) through the points of the late exercise period
If the anaerobic threshold has been exceeded then the lines will be different.
The point of intersection for the lines will identify the anaerobic threshold (AT):
((slope early) * (VO2 at AT) + (intercept early) =
= ((slope later) * (VO2 at AT)) + (intercept later)
VO2 in liters per minute at the anaerobic threshold =
= ((intercept later) - (intercept early)) / ((slope early) - (slope later))
VO2 at the anaerobic threshold in mL per kg per minute =
= (VO2 in liters per minute) * 1000 / (body weight in kilograms)
