Thanks for the tips - that's especially interesting about keeping your legs spinning, and changing to a small gear when the terrain is rough. I've just got back from another mtb ride with a buddy whose done a lot more than me and it was such a laugh. I felt like a bit of a clutz, especially on the narrow stuff with stones and roots but really enjoyed it. Couldn't quite belive I was riding some it. We also went up some quite steep hills, so we kept stopping to look at the view when we got to the top ( and have a bit of a chat.)

As for my legs, they felt good. Being out of the saddle a lot more felt like I'd given them a weights workout.

Might look into picking up a cheap 2nd hand bike - one with suspension folks maybe. At one point both my forearms were tingling like mad with the vibrations - although I managed to keep my grip relaxed.