Had a bike fitting several years ago. Now have developed a sore lower back after riding. It's worse the day after a ride. Does it mean I need to tweak my fit? Is a sore lower back indicative of one out of whack setting, like a saddle that's too far back?

Could you please post a picture of you on the bike with your legs in the 3 and 9 o'clock position? Please wear cycling shorts so that we can view the position of your knee. It may be that your seat is too far forward, which is causing your hands/shoulders and lower back to have to work to keep your torso upright.

Several years ago. It's more likely that you need to strengthen your core. Which does not mean doing crunches, quite the contrary.

I have no such picture, but I'll see about getting one. I do a few pushups and planks -- stopped doing crunches a few years ago.

I do a fair bit of back work at the gym: about 5 back exercises for every ab one. Squats are really good. This year I've started using Core Advantage. It's been great. I'm stepping my way through the programs, one a month.