The couch to 5K is one of the best beginner runner programs out there. It gently and smartly alternates walking and running together until you are running for 30 minutes straight. But a lot of clients that have never been runners before come up to me and tell me that at around week five they are hitting a wall. After a lot of tweaking with the program I found an easy solution to help break beyond that 5 week wall.
What I have my clients do is when they get to week five, or any week that just becomes a problem is to switch out the running portion of the workouts for steep incline walking. This allows an increase in heart rate and force production through hills without having to break stride. The problem most of my clients are facing is that they just don't have the muscular strength combined with the muscular endurance to run yet. This substitution method works very well and has help a lot of people.