Strapper, I don't know if you've played much sport. I remember, back in my largely misspent youth, being very sore after bowling in the nets for the first time after having a long break from cricket over winter. I've just assumed from then that that was what the second up syndrome was all about. After their first fair dinkum tilt from a long period of rest the horses'muscles are sore (just like I used to be). Dunno if this is right but it makes sense to me.