I am recovering very well after a diagnosed tibial stress fracture on Feb. 12.  I have resumed full running status with no problems.  ( the only difference is I train smarter and more patient now)  All of my training has been on completely flat rail -to - trail trails.  I would like to incorperate some gradually hilly trail runs.  Are there any suggestions as to a time frame to slowly mix some hills in?  I have been back to all-running every other day for the last two and a half weeks.  Thank you for any responses.