I knew Harry Wilson (Ovett’s coach) well, and John Anderson (Dave Moorcroft and Liz McColgan’s coach) very well indeed - and I listened as much to them as vice versa. For example, I separately asked them both - around the late 70’s - what place stretching and flexibility training had in their coaching - of Seb and Dave (Moorcroft) among others. And both said exactly the same thing. “Flexibility training makes runners go more slowly.” article by Pat Butcher on globerunner.org
MY COMMENT: Interesting! I still think flexibility gains importance the older you are- particularly in and around the hip area. I can't say first hand but I've read that Kenyans do plenty of stretching- doesn't appear to slow them down!