Hi,

Just a suggestion if you have lower back pain I've found a few things that help. If you already know either of these tips just ignore me ;-)

One; Have your trusty mechanic check the fit on your bike to identify any issues there. Your message doesn't say
how tall you are, I'm short (5'1"). Cycling was painful till I got women-specific handlebars.
Wow, braking and shifting at the same time without throwing out my shoulder, who knew?!

Two: Sure you need strong legs and aerobic fitness on long rides. But cyclists also need strong and
flexible core muscles that act as a base for all that pedaling. A few crunches will help
support your lower back. If you already do plenty of those the stretches aermail2 suggested
are good to keep those 6 pac abs flexible!

Three: I know it sounds silly but breathe! Especially on hills. One AIDS ride
rider I know sings on hills (makes sense, if you're singing, you must be breathing). Disco on
uphills for the cadence, r&b classics on downhills and flats. Just kidding on the last part.