Just as I reached the 90 second mark I am starting the plank challenge all over again.
The other day I noticed a slight twinge in my back. It continued the next day. Then I caught the reflection of my position in a glass door. My butt was higher than the rest of me. I was not flat like a plank, I was holding my rear too high. This explains why I was feeling something different in my lower back. I am giving myself a week and then starting over again - this time with a mirror so I can view my position easily.
Protecting the lower back - non-negotiable self care!