yeah, when he talks about waist rotation adding power - I don't see any waist rotation at all in his backhands. Is it a case of "what one feels they're doing" being very different from "what they're actually doing"? I know people use waist on big BH loops, but not Anders, not in this video anyway
That's exactly what I'm talking about. He feels his waist being used, so he teaches it. But how can you learn it by his demonstration? There's barely any visible waist movement! I've recently worked a lot on my BH, and let me explain what actually happens.
There are two keys to this "waist usage". First, it's not about the forward swing, it's about the back swing. Second, due to the smaller hitbox on the BH side, you need to reposition your body for every shot on the BH so the ball is as close to your optimal hitbox as possible, and this needs to be done in all 3 dimensions because the BH hitbox is smaller in all 3 dimension.
I'm gonna explain the 2nd point first. The hit box is small on the BH side, in all 3 dimensions, so
how do you get the ball into your hitbox, which is usually just left of your navel? It's pretty intuitive laterally, you just slide left and right. For the forward-back direction, foot movement is often not fast enough. Forward is usually fine, you move quicker in the forward direction, and if a ball comes slightly shorter than you expect, you can just wait, but if it comes a LOT more forward, then it's usually because it's a slow ball so you'd have time to just move forward. The issue is when it comes fast and long, and you don't have the time to move back.
To create space, you need to suck in your belly and bend your waist a bit to the left. This only gives you a couple inches of space, but that's invaluable. Next is the up-down direction, a higher ball is usually slower, so you'll have time to stand up straighter to get to the ball, but a lower ball is often faster and spinnier. Using only the arm to get to those balls doesn't give you enough time, you need to bend your legs to get to it, and since the important thing is to get the ball slightly left of you,
you'll bend your left leg a bit more.
Now what happens when you swing forward?
You simply tighten up all your core muscles. Your backswing would've made your left leg slightly more bent (i.e. your left hamstring more contracted and left quad more extended), and your left waist more bent (i.e. your left obliques more contracted). When you tighten up all your core muscles on both sides, your body will naturally stand straighter. Your legs level out, your waist straightens up.
It feels like you're rotating your whole body, and you are (though not very visible), but really you're just returning to a neutral position.
A couple of side points:
1) Why does doing this way add power to your shot? It's not really that tiny body rotation, per se. In physics, momentum must be conserved, so when you swing forward, there's an equal backward momentum on your body to balance the forward momentum. If your core is loose, then your core will absorb all the backward momentum, but if your core is tightened up, then the momentum is transferred to the earth beneath you. It's like running on track vs running on ice, if the ground beneath you isn't absorbing the backward momentum, then you're going nowhere.
2) You need to find your hitbox first. A lot of beginners don't even know where their hitbox is at. The forward-backward direction is often the toughest, as many beginners hit the ball too early or too late. You need to find your hitbox first before getting to the body usage stage, but that's an entirely separate tutorial. That's actually another pet peeve of mine, as many tutorials treat body usage on the BH side like they do on the FH side. They say power comes from the body, so they teach body usage first, but IMO that's wrong. On the BH side you need to learn arm usage first, because the key to body usage is positioning your body to get the ball as close as possible to your hitbox, and you can't do that until you find where your hitbox is with your arm first.
3) Note that the above is about near table BH play, when you're far from the table and want to launch a big loop, you'll need play the BH very much like the FH. You'd actively bend your left leg, twist your waist to the left, and then weight transfer to the right. You don't have time for that close to the table.