Figure 2: Ventilatory equivalents of O2 (VE/VO2, bold line) and CO2 (VE/VCO2, light line). The AT (arrow) is determined by marking the point (arrow) at which (VE/VO2) starts to increase while (VE/VCO2) remains constant or falls slightly (due to VE increasing disproportionately VO2 to but proportionately to VCO2).