Here’s a qualitative look at what critical volume is:
You have a friend that you can beat at the 5k, a 15 mile bike ride and a 400 TT in the pool even though that friend trains much more than you. However, when you go to the half iron distance he successfully beats you by 10 minutes. This is where critical volume comes in; he has gained the durability (through volume) to extend his speed potentials to longer race distances. What critical volume does is suggest how much training is required to gain the majority of the durability required for your race distance. At long distance races, this lack of durability is the major determiner of time loss for most people. Meet critical volume, and you will beat most people around your speed potential even though they may be faster than you at short distance racing. This is even more the case in IM racing where almost no one except some in the pro wave meet critical.
A lot of people misunderstand my critical volume posts to mean “he says you must do these huge training mileages to do well in IM…..that’s crazy”. That’s not what critical volume is about.