Peter,
Out of curiosity, what kind of biking?
Bikers (myself including when I was riding pretty religiously) are notorious for getting great workouts, but never hitting the core muscles (something about being hunched over, I guess, doesn't improve core muscles. :) )
While I'm not why your Lats are feeling it (honestly that sounds more like a bike fit issue) -- perhaps you've been doing a lot of climbing and pull hard?
Anyways, try the 8min ab workout or some variation. Easy way to pack in core fairly quickly.