An error attends doing exercises with overweight is tender to arch your back to help the movement positive. This is not recommended because the position of lumbar hyperlordosis press too the intervertebral discs and can cause injury.
Exercises in which we use the Bank We must ensure that our back is well supported to evenly distribute the weight over the entire vertebral column.
Usually is an excessive weight which leads us to adopt this posture from hyperflexion of the back down, pulling the hip forward so that they thus intervene more muscles in motion and get raise the dumbbell or bar.
Best to play it with a back injury must be cautious and adapt the weight to our chances. You have to be aware at all times that the position of our back is correct, there plays an important role the abdominals, which avoid this excess of bow at back.
There are people who by their training or have no force to control this arching uses training belt, passing it between your waist and the side, so stay well coupled support. This can be a bit like forcing the machine, but if the training required is a good solution.