Goosey
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I much prefer RDL's (with slight knee bend) and straight back as I'm very wary of my form with all types of deadlifts.
I think the way @Silverback; is describing it would be beneficial for the lower back strength but as with all exercises, starting light is an absolute necessity. I'd like to try this style, just thinking where I can fit it in as I tend to have a fair lower back pump after deadlifts as is. The lower back seems to be a tough one to determine the difference between working the muscle and injury.
Correct.
I think the spine needs flexion and extension, the lumbar extensors are like any other muscle and I think just 240 seconds a week is enough, you just got to be sure the the movement of resistance is right.