Doing a wall sit while you brush your teeth at night

I started doing this after I injured my knee and had trouble keeping to my PT exercises/ the thought of doing a wall sit without a distraction was terrible. I figured I could feed two birds with one scone by using the 30 second intervals of my electric toothbrush to do wall sits. I built up to the two minutes, and now I automatically do it without thinking when I brush my teeth at night. Results? Clean teeth and no knee pain.