I've been letting my fitness deteriorate a bit too much recently due to being too "busy." I've decided to get back into it and one thing I want to specifically work on is mental strength. I've decided to see how far I can take it with planks. For a rough baseline, I'm starting at roughly 67 seconds of planking before my body reaches the point where it feels like continuing would cause an injury. I'll try to see how far I can push it within a week or even a month.
The main concern is actually causing an injury which would at least be a sign of decent mental strength.