What does it mean if I can't keep my upper back straight ?

[mortac8]

@Silencer23

It sure feels great, and I don’t feel like I have trouble shifting to a higher gear and get up to my running, but everybody keep saying it’s the worst thing I can do and it’s taking away 0.1’s of secs of my race.

Who is ‘everybody’? Seems like you take too much advice.
Random note: Whenever people make some change then watch for it on video, the change is usually infinitesimal compared to what they are expecting to see.