Are you dreaming of a 5K run?
well I would not say that you should not run outside at all but running outside is certainly higher impact than running on a treadmill and/or using an elliptical or bike. if running outside is not causing pain you can certainly do it once in while but in general i would suggest that you use the treadmill, elliptical, or bike most of the time.
Jeremy Gentles, MA, CSCS
ObesityHelp Exercise Physiologist