he talks about the importance of some form speed work AFTER sessions .. ie, the ability to shift from slower to faster..
i definitely find myself struggling with this.. if i go into a run thinking 'slow', it's so hard for me to shift gears and get back into a fast mindset.. i've been working on that more lately, especially today.. seems so important.
http://www.youtube.com/watch?v=lICOI-CqNJo