My first reason goes back to the time when a guy named David Marmon hired me to be his graduate assistant. I remember my first day on the job. I wanted to get my workout in. Like a typical meathead, I went out and did some crunches, bench presses, and bicep curls. After my “gettin’ swole” workout, I sat back down in the office expecting some praise and admiration for my superior workout skills. David greeted me with, “Why do you train that way?” I was dumbfounded. I thought I had all the answers when it came to things like getting stronger, fitter, and leaner and all around more awesome. He followed his question with, “We train movements, not muscles.” I guess the idea of training movements, not muscles, kind of stuck with me (even though we still did sit-ups in our programming at the time). Train movements, not muscles.
So taking the train movements, not muscles approach, is bringing your sternum closer to your pelvis a movement you want to get better at? Think about it. When you squat, what are the coaching cues you hear? Chest out. Back flat. Hips back. Right? Same thing with deadlifts and many other exercises. Chest out. Back flat. The spine evolved to handle weight in the “chest out, hips back” position. That’s why we coach it that way. Why would we want to get better in producing force in any other way?