A Standard Weekly Workout Cycle The seven-day, or weekly, training cycle is as arbitrary as the seven-day week itself. Or is either really arbitrary? Have you ever wondered why the week is seven days long? Four weeks fit neatly in the 28-day lunar cycle, and that is not arbitrary. Human calendars in all societies are organized around terrestrial and celestial cycles. The Christian Bible says that God worked six days to create the universe and then rested one day, and that’s where the seven-day week comes from, and like many things in the Bible, this story may have a truth that is deeper than literal. Perhaps six days are about as long as the average person can work hard without rest. If this is true, then the seven-day training cycle is needful for the same reason that the seven-day week is. Creating a standard weekly workout schedule is not an absolute necessity, and there are a few noteworthy examples of runners who do not use them, including marathon world record holder Paula Radcliffe, who settled upon an eight-day cycle early in her career. But seven-day cycles work well for almost every runner, and in any case what is far more important than the exact number of days in the cycle is the repetitive, customized routine of the cycle itself. When you commit to doing certain types of workouts in a certain sequence over and over, you soon begin to observe predictable patterns in your body’s responses to training. You may notice that you almost always feel less fatigued and more ready to run the day after Sunday’s long run than you do after Tuesday’s intervals. Or you may notice that you typically perform better in Tuesday’s intervals when you do an easy run on Monday instead of not running at all. Such observations present valuable information that you can use to further customize your weekly routine. Even if the weekly routine you start out with is somewhat arbitrary (as mine was in high school), the emerging predictability of your body’s responses to it enables you to modify this schedule bit by bit to make it ever more productive for you. Undoubtedly, this is how Paula Radcliffe came to her eight-day cycle.