i do it on leg day because it hammers the hams. I generally do back on mon, and legs on fri. It does get a bit of work in lower back, but not as much as full deads. The way i do them is push my butt back to lower the weight, instead of "bending at the waist". To come up, I focus on pushing hips forward, which will raise the torso, and squeeze glutes hard at top. I get a little pump in lower back like I said, but I don't focus the work there.
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