Do you move your (lower) back back and forth during the exercise?
I find mixed recommendations online. so far, I think it is better to keep the lower back stiff and focus on arms, shoulders and upper back. Also, you don’t move the back when doing barbell rows which is the same movement.
For example, jeff nippard moves his back at 6:00 min in this video https://www.youtube.com/watch?v=PAXkl-AdJFg not as strong as others do, but still.
Here, they keep the back perfectly straight https://www.muscleandstrength.com/exercises/seated-row.html
In my gym many people (all that I witness) move their back.
If you want stimulus focused into your upper back then move lower as little as possible. Focus on the rowing movement. Pure rowing machines also have your back fixed. So nothing wrong with keeping back straight. I do find it easier to move heavier weights when getting assistance from the rest of the back. May be because of that you see folks move their back.
Buuuuuuuttttttt
At the other end is the flexion row where you not only move your back but flexing it allowing the spinal erectors do some work. I love this variant to compliment regular stiff back rows.
Experiment with both!
I find it harder to keep a strict no-back movement from when loading higher weight, but I try to cycle through: some 2-3 months i do higber weight lower reps (10-14), and then i scale back the weight and try to do higher reps (15-25). Honestly I have no idea which is better, but time will definitely tell. It’s best to just experiment around, really
I don’t think it matters much as long as you aren’t pulling hard with your lower back and it taking over for your upper back. If the movement is slow and smooth, your upper back/arms should be the limiting factor and feel it.
That being said, I do prefer to keep my back as still as possible.
