Last Friday, I went on a fairly strenuous shakedown ride of a carbon uberbike I've built. Both the stem and carbon aero handlebar reach were too long, so the ride was very stretched out. Not uncomfortable at the time, but off by nearly 2cm.
So I rode hard, and then I played 36 holes of disc golf. I began to feel tightness in my lower back. It twinged a few times, but I ignored it.
Then, later that morning, I got out the hedge trimmers and re-sculpted to tall holly bushes on the corners of our house. I bent to pick up all of the trimmings, stuffing them into lawn bags. Then I carried the bags down to the curb.
By evening I was pretty sore. By Saturday morning, I was really spasmed in pain. It's taken 5 days of stretching, ibuprofen, and rest to begin to feel better. I haven't been on a bike yet this week, although I've fixed two for neighbors.
It started by riding hard on a bike that clearly is not dialed in to fit. My bad.