Helpful Calculation Tool
I ran 11 1/2 miles this morning. I warmed up and then ran 4 hard miles (average 8:22/mi.), a 5 minute recovery jog and 4 harder miles (average 8:00/mi.) followed by a recovery jog. (I used this calculation tool to figure out my average pace for each four mile part of my run.) I liked the fact that the hard parts were divided by 5 minutes of easy running, but it was still a hard workout.