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.