I went out to go to work (and get breakfast on the way) and discovered a flat tire.
I went back inside, called my boss, and made breakfast. After sufficient caffeination I changed into cords and a sweatshirt I didn’t mind getting dirty and went out to deal with the tire. Only one was flat, and I had a spare, so time to change the tire.
I discovered that yes, even spreading the trunk mat on the ground to sit on, I get dirt all over my pants changing a tire. Why not crouch? Mainly I don’t trust my balance while crouching long enough to crank up the jack. Sitting was more comfortable.
I also found that my arms aren’t up to loosening machine-tightened lug nuts — but my legs are. No, I didn’t jump on the lug wrench. Stood with one foot on the wrench and I gradually increased the pressure.
So now I have 2 new tires (another was also very worn, and it’s preferred to replace tires in pairs or sets).