Its a pretty cool move. I did them un weighted for awhile, and they killed my hamstrings. Then I got used to them, so I added weight, (hugging a plate kettlebell or dumbbell) and they killed my hamstrings again.
It was a “new” move so it progressed fast and it was exciting. After awhile I started using a loaded barbell.
Eventually I got too excited about progressing back raises and went too heavy and started using too much lower back and less hams/glutes. Then they just started to make my back sore and tight.
Look up @ape288 Alec Enkiri’s vid on his YouTube about them. I have ran them like he noted in the past and loved them. I started doing them pulling 3-5 45s stacked together into my chest to work on my mid back and upper back as well. Seemed to help not only with glute/hamstring drive on deadlifts, but also with keeping shoulder back and tight from squeezing the plates.
I think if you are going to go real heavy on these you would be better off with 45 degrees, the horizontal position would put a lot of shear force on your spine at the top and that’s not really a good thing. Horizontal would be better to go light for high reps.
Curious as to why this is? In the horizontal version, maximum sheer is, as you say, at the top. With the 45 deg version, maximum sheer would occur when you are horizontal with the floor, which would be 45 degrees from the top, so in partial extension. Surely your spine is more stable at the top. fully contracted, than it is 45 degrees, and would be better placed to handle the higher sheer forces.
Genuine question, I have no experience with the move, just thinking out loud.
You know what, now that I think about it again maybe there is little if any difference. That was something I had heard a few times and it seemed to make sense, but we would need someone with sufficient knowledge in biomechanics to explain this. It could be that during dynamic movement there is less stress on the spine than holding still, which you would likely do for at least a moment at the top of a back raise. I’m really not sure as to the explanation, now you have me wondering.
I tried searching for something on that and I don’t see anything useful. The other possibility is that shear forces are higher when your torso is past horizontal and the horizontal version has you either there or at horizontal for the duration of the exercise. I don’t know all the finer points of shear forces but basically standing with a bar on your back, like a high bar squat, is pretty much all compressive force and very little shear. As you lean forward the shear increases, but at what point it decreases (if it does) I really don’t know.
Perhaps neither version is suited for heavy low rep work if you have back issues.
Olympic guys seem to like horizontal to floor, bar across shoulders. I guess arched back, like oly pulls.
As far as forces to look at for: Many 45 Degree models have handles outside and slightly in front on the hip pads. These handles are right where you hands end up at the top of the back raise holding a barbell. You can shear your poor pinkies off between the handles and the barbell if you’re not careful.