What is the 80% rule of running/racing? Well, explaining the "what" is easier than explaining the why. I'll share my belief of the "what" and leave the rest for others to ponder.
The 80% rule of racing means that 80% of a runner's race times will fit nicely in the middle of a bell curve. The remaining 20% can be divided roughly among two other categories. 10% will constitute sub-par races better known as having an "off day" race. The remaining 10% of races are the "on days". These are the days where everything is clicking. The mind feels a painless, unlabored race.
That's it. That's what the 80% rule of running/racing is in my opinion.
But "ugh" this is too short of a post so maybe sharing a little of the "why" is okay if no one objects.
First, we are all human beings. We have good days and bad days. Our bodies are better rested some days and more tired other days. We have life stresses which push us out of our norm some days and we have days where everything is a smooth as glass and easy as pie.
For a runner, the majority of the time we are training for a goal race but will run other races during the build up to this goal race. In all honesty, a runner should not expect to have a PR during these races. Although, this type occurrence does happen from time to time. The most likely result will be for a runner to field times somewhere well below their best ever efforts. But if a runner is not recovered enough or if the conditions on race day are less than ideal, a "King Kong" size monkey usually jumps on the runner's back as they struggle home – ready to get out of "dodge" as soon as they cross the finish line. Yes, it has happened to all of us at one time or another. Admit it. We have an "off day".
The converse is just as true. Take some extra rest or do some easier workouts or just have life treat the runner a little more gently and "shazam" the runner's legs feel light and frisky which allows him or her to possibly nudge down a PR by a second or two.
As I said above, the rest of the time the runner walks away from their race knowing they put in a solid effort and added another big stone to the training pyramid for their upcoming goal race.
And yes, the 80% rule applies not just to racing but to running in general.
Think of it this way. If someone could pick a stock right 90% of the time, he would make a pretty darn good stock broker. At least, he should be a wealthy stock broker.
90% of the time, a runner has good decent days of running. Good decent workouts build up fitness. However, the 10% of the "off days" don't constitute a loss of fitness. Actually the opposite is still occurring. Because the runner still went through the workout, they were still adding to their stock pile of fitness. The improvement physically might be much smaller but it was still improvement.
To summarize and provide a moral to the story 80% of the time, a runner does what is expected and builds on their fitness goals. 10% of the times, their workouts exceed their expectations and increases their confidence. 10% of the time, when a workout or race doesn't go as expected, it doesn't do anything to decrease their fitness. Fitness was still increased. What was really hurt was confidence.
The moral to the story is look for the positives in your training not the negatives.
Thoughts from the Cool Down Runner