I just wanted to add my 2-cents here. I got the Run Less, Run Faster book for Christmas and was very intrigued. Starting Jan 1 I began working my way through the programs beginning with the 5K. I didn't have a goal race in mind but I wanted to see if I would improve. I did the intervals and tempo on the treadmill so I could more easily control my pace. Once they got longer, I moved them outside. I did the three running workouts religiously but I slacked a lot on the XT. The program worked great initially. I ran a 5K time trial that was 3:30 faster than my PR. I found the tempo run to be the hardest, with the long run being the second hardest, and the intervals to be kind of easy. With all my new found success I decided to train for an Aug 1/2 marathon and an Oct marathon. I decided to start with the 1/2 training program (since it was longer) and then cut over to the full when I was the right time out for it to start. I worked through the 1/2 program without any problems but the wheels came off pretty quickly once I started the full program. I could no longer complete the long runs. The distances, combined with the heat, were at a pace that I couldn't sustain. I initially dropped my target pace by almost 90 seconds per mile with the justification that it was my first marathon and I didn't need to kill myself. Even then I couldn't hit the mileage requirements for the full marathon and I eventually stopped training on the program. I do think the program works but I now know that you'd better have the base to back up the program. I am considering using some of the workout principles this winter to improve my basic speed but I've learned that it's not a marathon training plan for beginners (and maybe even intermediate runners).

I think Marcus is right. The FIRST program isn't a short cut to training. They just substitute a cross training activity for 2 runs a week. You have to be going at building your "aerobic engine" with hard cardiovascular exercise at least 2 cross trains a week. Then you can carry that activity over to your running. Your engine is bigger from the diversified work load making your running better. As an older runner I'm sold on it even though I really struggle with the biking. It's harder than I thought by the hour and I've yet to complete a swim that I didn't feel like I was drowning.