deadlift, what do you think about my form?

[assito]

Hellow Mark,
I am doing starting strength now, but I can't hold my back stright all over the lift. In the warm-up sets I succeed to do it, and to do a regular deadlift, but in the work-set I do a straight leg deadlift, and not hold stright my back.
Here is a work set with 159 lbs.
http://youtube.com/watch?v=H6lvjW_nHfE

What do you think? how can I improve my form?

thanks!

[Mark Rippetoe]

This link doesn't work for me. If your ass is coming up before the bar, your hamstrings are not anchoring the back angle, and if your back is not staying flat your erectors are not keeping it that way. Sounds like you need to lower the weight and do your homework. And since 159 lbs. is not very heavy for most average sized men, I suspect you need to put on some bodyweight to get stronger.