The frames in the MD2-file have names. A subsequence is defined by a bunch of keyframes with the same name (or part of it), i.e. run1,run2,run3,run4....then the next sequence is started by stand1,stand2,stand3...
We have a thread somewhere here that deals with this topic too. The problem can be that in some models (i know one), the frame names are misused to write some text into the file instead of the frame names. In that case, you have to recreate the subs yourself. The thread contains some code to do this, too.