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

[RB34]

@Silencer23

thanks for all the comments.
Here’s a 35lbs tire start… sorry for the winding, tried to pre stretch the rope before I left.

http://www.youtube.com/watch?v=J7GWEbeK7pE

Self analysis - My hips were too high here- Perhaps a lighter tire

That 35lb pull seems too heavy, look like it’s slowing you down tooo much.