Out and Back Runs - Why They're Important

Ever notice that one side of your body (e.g., ankle, knee) is sore or strained after a run but the other side is fine?  Well it could be a result of running on a sloped roadway.  For drainage purposes roadways are created with a slope towards the outside of the road, which keeps the road from flooding during a rainstorm or melting of snow.  A slope of just 1 to 2%, which may appear almost flat to your naked eye, will deliver uneven stress to your body.
To avoid this uneven stress - especially to your lower extremities - run out and back routes as opposed to loop runs (staying on the same side of the street running in the same direction).  The objective is to keep the impact to your body even on both sides.  Running out and back on the same path (same side of the street on the way out and back) is helpful in doing this whereas loop runs put more stress on one side of the body.
I've been running loop runs for the past few weeks and I noticed an aching or strained feeling on the outside of my outer ankle and knee on one side, and on the inner side of my opposite ankle about 1 mile into my run.  Not thinking too much of the aching, I kept running, and paid the price when I was finished 4 miles later!  Since then I have been running out and backs - out and back on the same side of the street.  Though this type of running delivers even stresses to the body, you still have the uneven impact from running on a sloped roadway.
So those roads that flood during a rainstorm are your best bet for running since they should be flat from side to side! :)