Recovery, recovery, recovery.
Cross train swimming and only pull with your arms...get your cardio without using your leg muscles.
And, I cannot overstate how much an awesome massage therapist can do for legs that have become habitually knotted up, etc. It can take awhile to find the right one, but when you do...I find that even one massage every 6 weeks or so does wonders for putting me back together.
"The best rides are the ones where you bite off much more than you can chew, and live through it." ~ Doug Bradbury