Perhaps one of the biggest mistakes new runners make is not taking enough rest, or downtime as it is called in running circles, between long training segments or after marathons.
Understandably, putting your training on pause seems counter-intuitive after a great race. You want to capitalize on your fitness and continue to set new personal bests. Likewise, after a disappointing race, the last thing on your mind is resting; rather, you want revenge and you're anxious to get back on the starting line.
Many runners have Type-A personalities. Taking an unnecessary day off—or worse yet a full week off—is about as enjoyable as a trip to the dentist for a root canal. Some runners have an irrational fear that missing a few runs will dramatically diminish their fitness and that taking five to seven days off will completely ruin all the hard work they've put over the previous months.
Unfortunately, it's the mistake of not resting enough after a big race or a long training segment that can ultimately leads to plateaus in training and stagnant race results. Not only does resting for seven to 10 days have little negative impact on your current fitness, the long-term gains you will be able to make will enable you to continue to make consistent progress, year after year without overtraining.
Why You Need Downtime After Races
It doesn't matter if your main training focus was one big marathon or you just finished a long training segment that includes a variety of short races. Your body needs an extended period of rest to fully recover from and absorb the months of training you've put in. Failing to take the necessary downtime to fully recover will virtually ensure you plateau in your training.
Because shorter racing segments can vary from runner to runner, measuring the cumulative training effect and subsequent stress to the body is difficult. However, the marathon distance provides a constant variable that runners can use to measure how specific physiological systems are damaged during just one race.
The Science of Why You Need Downtime
One scientific study looked at the damage done to the calf muscles during a marathon race and concluded that both the "intensive training for, and the marathon itself, induce inflammation and muscle fiber necrosis that significantly impaired muscle power and durability".
This study makes it clear that your muscles are undoubtedly weakened and need extensive recovery before returning to full training. Given this study also examined calf muscles during an extended training block, the need for downtime applies to any arduous training segment.