In order to keep improving, you need to employ the principle of progressive overload. Progressive overload can be defined as the gradual increase of stress placed upon the body during exercise training. Progressive overload can be achieved in many different ways, including:
- Increasing your weight for the same number of reps.
- Performing more reps with the same amount of weight.
- Increasing the number of sets you perform.
- Decreasing your rest between sets.
- Altering your tempo and changing the amount of time your muscles are under tension (performing negatives, pause reps, or lifting more explosively.
- Using better form (greater efficiency)
- Increasing your range of motion.
- Performing more advanced variations of an exercise.
These are just some of many different strategies you can use. In terms of progressive overload, this exercise falls into category #8, but also #1. While the regular variation with my feet on the ground is already very challenging, the more advanced variation is on a whole other level of difficulty and requires a much greater amount of lumbo-pelvic stability, and also shoulder/scapular stability.
By elevating my feet on a wall, versus resting them on the floor, I am required to support a significantly greater amount of my bodyweight. Incorporating the knee tuck adds in another challenging dimension, and demands drastically more full body strength and stability.
I also tried the knee tuck on the same side of my body that was rowing (ipsilateral) and it did not go quite as well, so it is something I will work towards doing. I stuck to the contralateral variation. You can't see it in the video, but I fastened the band to a very heavy kettlebell.
To get a detailed description (coaching tips) of how to do the basic variation, view this blog post that I did a while back. Aside from the knee tuck, the form is the same for both of these exercises.