Something seems wrong
Something seems wrong with those equations. For a level ground running velocity of 300m/min, VO2=63.5
VO2 = (300 x 0.2) + 3.5 = 63.5
That sounds reasonable for a VO2 at that speed. However, when you go to the graded VO2 equation, things get messy.
VO2 = velocity x grade x 1.8 (over-ground running)
If we use the same velocity of 300m/min and a grade of 2%, we get:
VO2 = 300 x 0.02 x 1.8 = 10.8
In order to have the same VO2 of 63.5 while running up a 2% grade:
VO2 = velocity x grade x 1.8
VO2/1.8 = velocity x grade
63.5/1.8 = velocity x 0.02
velocity = 1763.9m/min
This is obviously WAY too fast
If we're calculating a relative VO2, then body weight must be taken into account; if an absolute VO2, then it won't be needed.
If you have a link to those equations post it and I'll try to fiddle with them some.