THE EE WAS REMOVING BOLTS ON A PIPE VALVE. WHILE DOING SO THE EE OVER REACHED WHILE EXERTING FORCE USING A WRENCH. THE EE REPORTED THAT HIS RT. SHOULDER WAS SORE ON 7/7/03 BUT DID NOT WISH TO SEEK MEDICAL ATTENTION. ON 7/18/03 THE EE SOUGHT MEDICAL ATTENTION AND WAS PLACED ON MODIFIED DUTY.