That doesn't really answer my question Thompson, you put forward the statement:

"By the way, a little figure for those here who might be green-ish - switching one person's commute of four miles (6.5km), which is the average length of a commute, from a car to a bicycle saves half a ton of CO2 a year - which is 5% of the average person's carbon footprint. Add in lots of cycling to the shops and to meet buddies in the cafe, etc, and you can really cut down that carbon use"

Does this figure take into account the volume of CO2 emitted by a human being taking exercise on a cycle over the same distance, or is it merely the drop in CO2 used by a motor vehicle.