Gross economy

Definition

“Gross economy” is the energy efficiency of the entire system of body and, where applicable, equipment at constant load, expressed as oxygen consumption per unit of power produced. The term is used mainly in cycling and describes how much oxygen is required for one watt of mechanical power. In the lab it depends on riding position, pedalling technique and biomechanical coordination; in the field, aerodynamics is added.

Why it matters

Two athletes with identical VO2max can be very different in speed on the road. Whoever needs less oxygen per watt sustains a higher power at the same metabolic strain, or the same power for longer. Economy is thus the third pillar of endurance performance alongside maximal oxygen uptake and threshold position.

Its course across the test stages also reveals the state of the system. If oxygen demand per watt rises already at low stages, that points to coordinative deficits, an unfavourable position or fatigue.

Originally relative values were used, i.e. VO2 in mL/min/kg divided by watts per kilogram. Since body mass cancels out mathematically, the value is mostly found in absolute numbers today.

Gross economy [mL/min/W] = VO2 [mL/min] / power [W]

How obseed measures it

Gross economy can only be determined with spiroergometry, because oxygen consumption comes directly from breath-gas analysis. obseed takes the values from metabolic diagnostics and stores them in the performance values together with the ventilatory thresholds and VO2max.

Economy cannot be calculated from wearable data. What sports watches report as “running efficiency” or similar metrics are estimates from heart rate and pace and are not comparable with the laboratory measure. obseed therefore only shows the measured value and uses the Efficiency Factor as a field approximation for tracking progress.

Gross economy is an important tool for defining individual, physiological training zones. Its course, combined with the thresholds, gives a comprehensive metabolic picture of performance capacity.

Example

An athlete completes a step test on the ergometer. At 200 W spiroergometry measures an oxygen uptake of 2,800 mL/min, at 300 W 4,050 mL/min.

200 W:  2,800 mL/min / 200 W = 14.0 mL/min/W
300 W:  4,050 mL/min / 300 W = 13.5 mL/min/W

Oxygen demand per watt drops slightly with intensity, which speaks for a stable pedalling technique. After a change of riding position the same athlete measures only 3,900 mL/min at 300 W, i.e. 13.0 mL/min/W. With an unchanged VO2max of 4,500 mL/min that corresponds to roughly 13 W more at threshold on paper.