The NAVY BLUE curve shows the metabolic demand at a steady-state and as a function of power/speed (mathematically speaking, time is infinite here). We could have also used energy demand instead, which would have then be displayed in kJ or kcal. Remember that 1 liter of VO2 delivers approximately 21 kJ of metabolic energy per minute. Therefore, the two can be used interchangeably. INSCYD using oxygen uptake in ml/min/kg instead of kJ or kcal to display energy demand because it makes it easier to compare to the actual oxygen uptake. Therefore the increment of oxygen demand in relation to the intensity also shows efficiency.
The LIGHT BLUE curve shows the actual oxygen uptake VO2 in steady-state conditions. At low intensities (power/speed), there is no significant difference between the actual oxygen demand and the actual oxygen uptake. This means that more or less all the needed oxygen (or energy) is covered by aerobic metabolism. At higher intensities, though, there is a gap opening up – marked by the BLUE AREA. This gap can be called the glycolytic or anaerobic gap. It is the difference between the oxygen needed and the actual oxygen uptake.
Athletes with a high glycolytic capacity (high VLamax) show a more significant gap compared to athletes with a lower glycolytic capacity (lower VLamax). This proves that a highly developed glycolytic metabolism (developed through training and/or only by predisposition) gets more dominant as a source of energy supply. In contrast: in an athlete with a high VO2max(highly developed aerobic metabolism) and low VLamax, you will be able to see only a small glycolytic gap, proving the dominance of the aerobic metabolism over the anaerobic.