MET: metabolic equivalent
MET is the ratio of oxygen consumption on load to oxygen consumption on resting. The oxygen consumption at rest is 3.5 ml per kg per minute.
The MET value for ergometer and treadmill will be differently calculated:
for Ergometer:
L = Load in Watt and
G = Weight in kg,
the formula applies:
MET = 1 + (12 * L) / (3.5 * G)
Thereby is the oxygen consumption 3,5 ml/kg per minute in resting, 12*( Load/kg) is the additional oxygen consumption ml/kg and per minute on stress.
This leads to the formula above.
Source:
Rost, R. & Hollmann, W. (1982): Stress tests in practice ( German: Belastungsuntersuchungen in der Praxis. Publisher: Georg Thieme, Stuttgart, New York. 164 p.
In other words, the formula is:
MET = 1 + (L / G) * 3,428
Note: other authors use a slightly different factor. (for example Jonathan Myers: MET = 1 + (L / G) * 3,486)
for Treadmill ergometry:
v = Speed in Meter per Minute and
m = Slope in % applies
a) Walking (<= 4.3 miles per hour)
MET = 1 + (v * (0.1 + m * 0.018)) / 3.5
thereby is
v * 0.1 the relative oxygen consumption in horizontal direction and
v * m * 0.018 is the relative oxygen consumption in vertical direction
b) Running (> 4.3 miles per hour)
MET = 1 + (v * (0.2 + m * 0.009)) / 3.5
thereby is
v * 0.2 the relative oxygen consumption in horizontal direction and
v * m * 0.009 the relative oxygen consumption in vertical direction
(Source: ACSM)