I've never had soarness in my fingers before and I've pushed them beyond the limit at like a million bpm (slight exageration :-)...Your comparison with working out makes alot of sence though. I'm sure there is some truth in that. I have a friend who expirienced the same thing but it turned out to Arthritis...lets hope its not. I think he got that from playing with his guitar hanging too low though. Anyway good luck.
-Garret