Bullet proof your knees with this exercise.
Get a resistance band and attached it around a rig or squat rack. Stand away from the rig and put on leg into the band so that it is nice and tight.
Then perform a single leg squat so that the band is pulling your knee towards the rack. Allow the knee to flex and push the knee over the big toe on your foot. Then contract your quad and pull your knee back so that your leg is straight and locked out.
You can also perform this whilst standing on a weight plate or step to increase the range of motion in the knee during the single leg squat movement.
This can really help with quad activation and engagement and also glutei stability, which in turn can really help people who have patella tracking issues or general patella tendinopathy/tendonitis.