JJ, swimming was ok, not crawl though - that was still too much stress on the affected muscle. Cycling with low resistance seems to be best (but unbelievably boring ). I don't have lower back pain so the cycle position is ok for me. I've been doing upper body weights too so my arms are getting quite toned!
After two weeks your fitness loss is minimal, but we'll start with lower mileage and easy paces until you feel more confident that the injury has cleared up. So once you are ready again, repeat the health check, and we'll gauge a distance from how that goes. I should think up to about 8k easy once you are ready to go. We'll take 2-3 weeks to get the distances back up, no speed work for the moment.