I have Mollie on Cosequin and fish body oil..I massage her legs and hips , when she has been lying down for a while, and it seems to help her...She now comes to me when she is sore, so I can massage her legs....

It could yes, just from the walking. Think of a car engine - warm summer days, starts no problem and gets up to optimum running temperture quickly.
Cold mornings, takes a bit more effort to turn over initially and takes longer to warm up, especially to get warm air circulating through the heater system.

If you equate that to an older dog, it can take far less for a lactic problem to occur. My Willow gets it if a walk is just ten minutes longer than usual, but the warm up / cool down has made a huge difference.
*If* your lad is having a lactic acid prob, it can take very little indeed for it to occur but its far from insurmountable to ease it.
As you are now doing agility [ so pleased you had a good time btw ], its worth you investing in the DVD from one of the links I gave you [ the Galen Therapy one ], and even if its not lactic acid but more athritis orientated with Eddys stiffness, that particular technique can hopefully still help loosen him up nicely for general comfort plus most dogs thoroughly enjoy having it done which is a very nice bonus

Thanks guys,

goes to google cosequin. He already has cod liver oil daily and glucosamine and chrondoitin twice daily - when he eats it that is...

Thanks Patch, for the advice - will take a look for payday!