So W7R1 I failed at, having to have a 5-minute break in the middle, because it was the first time I ran outside and I took off faaaaaaaaaaaar too fast. And then my back was hurting and I was worried about an old injury, so I took an extra rest day.
But today I set off carefully and maintained a slower speed, and I finished W7R2 quite easily, despite pouring rain and wind, and my back so far feels fine. I did lots of careful stretching, especially hamstrings, afterwards, but I suppose tomorrow will be the test. If I wake up and it's painful I might have to go back to the dreadmill.