Metabolic demand refers to the amount of energy needed for a certain intensity. It would be applicable to express metabolic demand in energy over time – like the mechanical power output as measured by a powermeter on a bike (for example is in Watt = J/s). However, for easy comparison with other physiological metrics, metabolic demand is expressed in needed oxygen uptake. This is a common term in the literature named ‘VO2tot’ – describing the total oxygen needed for a certain power output or speed. As it is expressed in ml/min/kg, it is very comparable to the actual oxygen uptake (VO2) and other metrics. The relation of metabolic demand (VO2tot) to speed or power describes the economy.