The 400 meter intervals were programmed by using a formula from Army Field Manual 21-20: Physical Fitness Training. You obtain the working time of your 400 meter interval by dividing your goal 2-mile run (2MR) by 8 and then subtracting 5 seconds. Using this formula and a goal time of 13:00 my 400 meter time was 1:32. Then you determine your resting time between intervals by doubling your running time. During the course of our training we identified that we were running the 400s far too fast, often finishing faster than 1:20 and never exceeding 1:32. My concern was that I was training a motor pattern that my cardio-respiratory system could not sustain for more than 2 minutes.
After 2 weeks we switched to 800 meter intervals using a similar formula, dividing our goal 2MR by 4 and subtracting 10 seconds giving us a goal of 3:05 per interval. Because this was a slightly slower pace than we had been running in our 400 meter intervals we gave ourselves relatively less recovery time, resting 5 minutes in between intervals. The 400-meter intervals were the key to getting us out of our comfort zone of the weight room and running again while allowing us to experience a degree of success and not beat us down mentally, while the 800-meter intervals were more effective in establishing a sustainable motor pattern.