Scientific Measure of Effort

Firstly, marathon runners should whenever possible live in either a bungalow, or an apartment with elevators.

I came up with a fantastic measure of effort expended relative to distance run, particularly relevant to long distances. It is called the stairs measure. The theory goes, that the ease at which you can climb or descend a flight of stairs, is directly proportional to the effects of the effort spent. It is measured on a scale of 1 to 10, 10 being the most effort required, and so the most effort spent.
Day 1, post race, level 9, in that I can barely get up or down the stairs, with 10 meaning a total inability to do either.
Day 2, level 7, sideways is still required going up and down, but can be done in less than 3 minutes.
Day 3, level 4, a normal step up and down is now possible, although with some discomfort.
Day 4, level 3, up and down the stairs is relatively easy, although with a tightness in the calfs. Level 3 is the most dangerous level. It is when the runner now decides that they have reached the level on the scale at which they can start running again. It is the level at which the runner then establishes that it is not in fact when running should begin again, although by virtue of the fact that they made this mistake, they now return to level 5.

Apply the stairs test to any run, wait until at least level 2 before running again. This is when the stairs are easy, up and down. Not sideways required, no one asks you have you injured yourself, and you stop walking 'funny' as per a 4 year old.