If you’re like many other endurance athletes, you have probably followed a readymade training plan at one time or another. Perhaps you found it in a book, or maybe you purchased it online from a website such as Final Surge or TrainingPeaks. If so, then you know that readymade plans are generally classified by race distance and level. For example, if you’re a relatively new runner interested in training for your first marathon, you will likely choose a beginner-level marathon plan.

Choosing the right level is not always easy, though, especially when there are a lot of levels. I have online running and triathlon plans that come in as many as 10 levels at each major race distance. Not a week goes by without my receiving at leas one email from an athlete asking, “Which level should I choose?” These athletes always tell me a little about themselves so that I have something on which to base my recommendation. More often than not, the information these athletes choose to share with me is either their time goal for the distance at which they intend to race or their best or most recent time for the same distance. This has always seemed odd to me, because time goals are almost completely irrelevant to training plan selection.

To understand why, consider the hypothetical example of a runner who wants to run a marathon in 3:45. If this runner should come to me and ask which level of marathon plan I recommend for a runner who has this goal, and his name is Wilson Kipsang, I will tell him he does not need to train at all, because I know that Wilson Kipsang has run 2:03 for the marathon on four separate occasions, and a man who is capable of running a 2:03 marathon can run a 3:45 marathon on no formal training whatsoever.

Now suppose instead that the runner targeting a 3:45 marathon who comes to me for help with training plan selection is not Wilson Kipsang but a 44-year-old woman who has run six past marathons and has a current PR of 4:22. I would need a little more information to be sure, but it is likely that I would tell this athlete that no training plan could possibly deliver her to a 3:45 marathon. She could quit her job, send her children to live with their grandparents, and devote her life to pursuing this goal and never achieve it.

What this rather extreme hypothetical example demonstrates is that there is no single training plan that fits all athletes pursuing any given race performance goal. So if time goals are not the appropriate basis for training plan selection, what is? Simple: training history.

Numbers aside, the goal that every athlete shares is improvement, which tends to occur in modest increments and is made possible by modest increases in training load. Your next training plan should therefore be one that administers a training load that is slightly greater than the highest training load you handled successfully in preparing for a prior race of the same distance you’re targeting this time around. For example, if you built up to 45 miles per week in preparing for your last marathon, build up to 50 miles next time.

Note that increasing the training load is not the only way to improve, so you shouldn’t feel compelled to keep training more and more each time you set your sights on a PR. You can also improve by making better use of the volume of training you’re already doing, for example by doing less training at moderate intensity and more at low and high intensities.

Indeed, if your current training formula is already a good fit for you, you can improve without changing it at all. That’s because you are not the same athlete at the end of a training cycle as you were at the beginning. For example, if you complete an 18-week marathon build-up, then take it easy for three weeks, and then repeat the same 18-week cycle, you will start the second cycle fitter than you did the previous one, so the same training will develop your running ability even further.

I’ve gone off on a bit of a tangent so I’ll just stop here.