Couch to 5k is a GREAT program. I'm just starting week six and I love it. I opted to try this program on the treamill and adjusting the speed is really no hastle. If anything it keeps me focused on walking/jogging at the correct times. I'm walking at 3.0 and jogging at 5.0 and that seems to be the ideal speed for me. Most treadmills even have a "walk" "jog" "run" button that you can press to adjust the speed easily. This program starts from very easy to pushing yourself as hard as you can. The first three weeks may even feel too easy, don't push yourself to extend the workout. The purpose of it is to build your muscles gradually so that you have the muscle and stamina to complete each week that follows. This program is great for first time runners (like myself) or for someon who would like to get back into shape. Good luck!