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

[RB34]

@Silencer23

Alright heres another 30m block start from today:
Following that thread I:

1. Made sure I squeezed the glutes hard to create forward motion
2. tied a longer rope to the tire (oh but that isn’t on that film, soon i’ll upload)
3. TRIED to watch my head position… What I did this time is I rolled my eyeballs upwards to look a few meters ahead instead of on my hips …

Are we progressing here ?
http://www.youtube.com/watch?v=_IYeoVM4PZs

tire:
http://www.youtube.com/watch?v=VxXmJQz_TO8

Are these block starts full speed? You need to be more explosive out of the blocks.