Check his temperature to see if he's running a fever. Is he drinking plenty of water? I usually don't give them more then a day or two being off their feed before calling a vet.
Also, with a strenuous excersize routine, he could be suffering from ulcers, something else to check...
"Be a best friend, tell the truth, and overuse I love you
Go to work, do your best, don't outsmart your common sense
Never let your prayin knees get lazy
And love like crazy"