Running, see page 144 of the PHB<br/><br/>You can run up to as many rounds as your Constitution score (NOT modifier, but actual score), after which you must make a DC 10 CON check to continue running.  You must make a check each round, and the check difficulty increases by 1, for each check you make.  If you fail, you may no longer continue to run and must rest 1 minute (10 rounds), before running again.  During this rest period a character can move no faster than a normal move action.<br/><br/>For example, a person with a 9 CON score can run up to 9 rounds, however on the tenth round he must make his first CON check at DC 10, if he succeeds he may continue to run.  However, next round he must make another check at DC 11, then DC 12...and so on, however if he fails, he must stop running and must rest at least 10 rounds before running again.<br/><br/>However, a person with a 14 CON score can run up to 14 rounds before making his first check, then on the 15th round he makes a DC 10 CON check to continue running.  And same with the previous example, the check DC goes up to DC 11 on round 16, DC 12 on round 17, and so on... when he fails he must rest for at least 10 rounds before running again.<br/><br/>A person with a 20 CON, can run for up to 20 rounds before making his first check, however the same rules apply...on the 21st round, he must pass a DC 10 CON check to continue running.  The 22nd round DC 11, and so on.