When I started c25k, I was able to do all the routines without stopping until I hit week 5. I took a break from the program and started working on my stamina. This was the routine I did: run 30 seconds, walk a minute on and off 30 minutes. Once I felt comfortable running longer, I would run 1 minute and walk for 2 minutes for 30 minutes. Then I finally upped it to 1.5 minutes and walked for 3 minutes. I read his article saying that if you run for X amount of minutes and then double that time for walking that it will help your stamina and increase your distance in running. At first, I started at 4.3 mph on the treadmill running and I was able to work up o 4.5-4.8. But don't start out running fast. Do what is comfortable for you. Also if you're new at running, don't run day after day. Make sure you have a rest day in between you're running days so you don't hurt yourself. I normally lift weights or ride the bike on my rest days. if your calves are hurting after a run, ride the bike for at least 15 minutes and it'll help elevate the pain.