The Grinch said...
You're getting old Willy and you need to warm it up before you do anything.
I go to a sports therapist and he showed my some good stretches to do.
One is to lay on the floor on your back. With your legs straight out and together, start with your left leg. Bring your left knee up till your heel is by your right knee, then kick your leg out gently in a circle, as wide as you can, back to the starting point. Like a frog kick. Dont let your heel get more than 5 cm off the floor.
Do that ten times each leg morning and night. You will be all better.
OK, I started doing it last night. Not sure if it's the answer, but it can't hurt. Core exercises are really important, but I always seem to let the crunches etc slide if I'm getting plenty of sailing done, because I like to rest totally afterwards. Bad idea. Must...keep...lower...back...STRONG!!!