I used to always do back ext. Now i do 3/4 deadlifts using the 5x5 rep scheme. I do my shrugs on the same day as back. Maybe that is why? I use good form. I don't get it.
Yeah, I've had minor back pain since I was a teenager, only from time to time though. Not constant. Been to the chiroprasctor a handful of times for a couple of weels at a time. I did herniate a disc almost 2 years ago, the one between L5 and S1 (very bottom).
No good mornings. I did back ext for the longest time. My back sways way in (chicks think I got a nice ass, it sways in so much).
Couldn't tell you how strong my core is. Today I did 3/4 deadlifts with 315lbs (you can laugh) with a 5x5 rep scheme Needsize style. I just went back to regular squats and dead(which I didn't do very often at all) about 2 months ago, because I finally decided it's all about size, however I gotta get there (and you gotta have deads and squats), and also because i finally got up the courage after having the herniation i had.
It's hard to say with shrugs. Make sure you're not using momentum to bring the weights up; you could be leaning back slightly (this will put stress on your lower back).
Your arms should remain totally straight, and rigid. Your traps should be the only thing moving the weight.