"I was reading a book on lifting for runners and hurdlers from the late 70s by John Jesse, and he mentioned that runners tend to have overdeveloped chest muscles (eg pectorals) and underdeveloped upper back and neck extensors, which contributes to "round shoulders" and a hunched-over posture when an athlete is tired at the end of a race. Thoughts?"
MOST people in general, runners or not, have or develop over time overdeveloped chest compared to upper back/neck. Google: Upper Cross Syndrome. Also Google: Lower Cross Syndrome. They are old school descriptions of common problems.
However, I haven't seen too many runners with any sort of overdeveloped chest. If anything it would be the opposite. I have however seen many runners with a tight lower back and look "fat" with a overly rounded stomach. Runners tend to develop an anterior tilt in the pelvis which leads to that old school Lower Cross Syndrome.
As far as the 185x5 thing....you're reading far too much into those numbers. It was a general example and I pulled those numbers out of the sky, it could be 85x5 for all I care. It's about the execution, not the numbers.
Also, there's nothing wrong with pushups. If someone is so phobic about creating muscle or fear the iron in anyway then do explosive pushups or feet elevated pushups or deficit pushups:
1. Explosive Pushup 1: Pushup, on the up portion explode up and bring your entire body off the ground.
2. Explosive Pushup 2: Same as #1 except only bring your upper body off the ground...aka "clapping pushup"
3. Feet Elevated Pushups: Pushups with feet on a box, step, chair, etc
4. Deficit Pushups: Hands on yoga blocks or steps or some other way to raise your hands.
Other ways to make pushups more intense: spider man pushups, single leg pushups, med ball pushups, traveling pushups, weighted pushups....