in mid april my partner had neuro surgery in her low back, in the area of L 4-5, had to go through a lot of the big muscle to get to the problem. she was sore for a couple weeks. the tried some short easy sessions on the trainer. then at a month a couple of gentle short (<20 km) rides. we are going to try a longer rides this weekend. she is uncomfortable if she flexes in the wrong way.
ps, walking helped, go for lots of walks.