Week 7 is going to start testing your endurance. Hopefully you are up for this test. The next four weeks of the training will solidify your endurance as well as your speed. If you find the speed too difficult to maintain, back off, but realize the speed you move down to is now the speed you can expect to be for the Half Marathon.
Week Seven program:
Sunday, Friday - off
Monday, Tuesday, 5 miles Easy Run (under 70% HRM)
Thursday - 4 miles easy (under 70% HRM)
Wednesday - 6 miles Tempo (80-88% HRM) This you will do by warming up one mile under 70% MHR, then alternate between 2 minutes under 70% HRM and 9 minutes 80-88%, then again between 2 minutes under 70% HRM and 9 minutes 80-88%of your HRM, etc., to a distance of 5.5 miles and then a half mile cool down.
Saturday - 11 miles (under 70% first 8 miles, 70-80% last two miles)
You have now built up to 9 minutes for a Tempo Workout.