Ahh, the Roman Chair! I saw a variation of that when I was going to LifeTime.. and I was doing exactly what you suggested, using a light plate. I completely forgot about this one! We'd also do it while turned 90Ā° to work the obliques.I was having lower back issues especially when I would dead lift or squat heavy. I started finishing off with an exercise where you bend forward and on an angled bench then lift your upper half by your lower back muscles. I wish I knew the actual name for the bench but it's usually at a 45 degree angle with pads for your thighs and it holds the back of your heels in. I do that with a 10-25 lbs. plate. That plus strengthening my core helped a ton.
Edit: This is it. Every gym I've been to has one.
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I'm at Planet Fitness now, will need to see if they have one. Well, when I get back to getting to the gym.