WOW! Thanks everyone. Feeling a bit overwhelmed with all of the posts and guidance.
I think it's definitely a combination of using new muscles (I haven't quite lost the belly yet!), lack of strength, and technique.
Leroy, the doc and the chiro has given me the all-clear in terms of any bone damage or disc involvement. He's really good and I have been seing him for years, usually only once or twice to fix problems, so he's not a leach like I know some can be.
It's definitely muscular. Seems to be at all the attachment points; the lower lats, where they attach at the back and ribs, and lower back where the glutes attach. Sitting at a computer for a job all day doesn't help at all.
I got to a point where I was feeling good, then went out again and probably got a bit too excited. So I need to just rest it.
I also think a few of you were spot-on with technique issues. I have gone in hard since I discovered my new passion, and probably need to ease up and weight for my body to adapt.
Thanks for the article link
CMC!
I have recently helped someone out who is going to in-turn help me a bit with technique, which will definitely be a good thing.
Laceys, I think you have something with the laying loose comment - I notice I get very tense, so I will keep an eye on it.
I saw a very excellent sports physio when I tore a calf muscle, and I am thinking I may seek a consult with him to get some guidance on strengthening and stretching.
What can I say, there's a lot of love on the water.
cheers everyone.
See you out there real soon