Hi Wendy!
How long have you been running 4 miles 4 times per week? If you have been doing this for more than 6 weeks, chances are your body has gotten used to it and needs some variety to shock it. Try incorporating some hills or sprints into your runs if you have not already. Also, on occasion, do Imax 2 twice a week (put at least three days between those workouts) to add variety.
Since you ask about some DVD's to throw in the mix, I would suggest KPC and Legs and Glutes. This would introduce some new moves, as well as new cardio and strength benefits to keep the variety and results going.
Here is a rotation idea:
Mon: Imax 2
Tues: Run with some sprints at the end
Wed: Legs and Glutes
Thurs: Pyramid Upper Body
Fri: Imax 2 (only once every two or three weeks...other weeks do a run with some hills)
Sat: KPC (alternate this every other week with Muscle Max)
Sun: Off
Do the above for three weeks and then mix it up again with another rotation.
Eat clean, drink lots of water, sleep hard, and deep stretch 10 minutes after every workout.
Stay focused...you'll look great this October
