Another way of thinking about it is that your foot can’t come off the ground if there is mass above it (your torso). If you lean forward the bodymass is distributed over a larger horizontal distance. If you were totally errect you’d only have to wait for the breadth of your body (from belly button to butt) to pass over the foot. If you are leaning forward you have to wait from tip of nose to butt (and with an extreme !!! 90 degree forward lean nose-back-butt) to pass completely over the foot before it can come off the ground. This increases GCT and ultimately slows you down.
Ah ok, that makes a lot more sense. It’s so cool on here to always be learning new stuff!
I used to describe it this way to my athletes. Extra trunk lean or actually reaching out(intentional of not) with the lead foot will lead to a touchdown further out front which will take much longer for the trunk to pass over that position. For comparison, I’d then demonstrate the footstrike being placed directly (or nearly so) under the torso and then point out that you would pass this point (with the torso) of that particular footstrike much quicker than the first example.
Perhaps it is a more effective visual demonstration than to describe it:) .
With a tall, vertically positioned torso, it is so much more difficult to even have the footstrike further forward. If the athlete is in the high hip position, it is virtually impossible to have a footstrike very far out front.
Additionally, the first example leads to almost assuredly, a flat footstrike and the second example would likely result in a ball-of-the-foot landing. Easy to see which one of those is going to be better for generating speed or maintaining the current speed. Hope that helps.
Yeah that does help thank you.
No problem-glad to help 
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