I read what he said as “you are only as strong as the weakest link”. You can have all the hip strength in the world, but if the hamstring (knee) buckles under the load you aren’t going to be going any faster. Gotta be balanced.
It’s also very obvious if you know, but measuring circumference is measuring both ham and quad mass. Charlie’s books say the upper ham/glute tie in is KEY (it’s also where I’m weak and working on hard right now).
John