Figure 1. The carbon dioxide output (V̇CO2) versus oxygen uptake (V̇O2) relationship. The metabolic threshold (V̇O2θ) is identified at the point at which V̇CO2 increases out of proportion to the increase in V̇O2. V̇O2θ is identified on the x-axis at a value of 1.40 L/min. The horizontal line at V̇CO2 = 1.75 L/min represents the ventilatory threshold (V̇CO2θ) as determined in Figure 2. The line of identify intersects the origin of the x- and y-axes.