When we talk about free-weight exercises, such as the Bent-Over Row and Pendlay Row, your body is in a strange position, almost parallel to the ground (or even completely parallel when performing the Pendlay Row, depending on your mobility and your body structure), therefore good stability and mobility are essential to perform the exercises properly and get 100% out of them.
Mobility can be improved by performing daily stretches and specific exercises, and I highly recommend that you do a proper warm-up before every workout in order to avoid unwanted injuries, make the body ready, and create a better mind-muscle connection.
When it comes to stability, your core has an essential role, therefore developing your abdominal muscles will have a positive impact on your performance, besides the visual benefits. A helpful tool in this situation is a lifting belt, which acts as a second set of abdominal muscles.
By increasing the stability, your overall performance will get better, and you will be able to increase the weight over time. A lifting belt will simply accelerate this process by offering extra support, but it’s important to keep in mind that it will not do the work for you. It is still your job to have a good form and maintain a neutral spine when performing the exercises.