Dwight Duab: The inverted row is much easier to do beginning wise than a regular pull up. And so it's the beginning phase of wanting to do a pull up but also by adding the ball it adds another dimension that makes it much more difficult to do. By placing it in that position with their feet on the physioball it allows them to have to stabilize with their core but yet still getting the rolling effect associate with the exercise.
It turns out to be a Lat exercise, a Latissimus exercise; however it also turns out to be an additional core exercise because they have to stabilize their entire body
in a straight plane. Making sure that their body does stay in a straight plane is number one. Making sure that their hips don't drop down to the floor, making sure that they go into a full extension with their arms so that they have to get full range of motion with their arms, and then trying to make sure that they have their feet equally distributed on either side of the balls so the ball doesn't roll out away from then. Sets and reps for that particular exercise are normal between six and eight repetitions, as many as ten, depending upon the training phase that you're in, and three to four sets.