“Don’t worry about bad sleep the night before a race; what matters is your sleep two nights before the race,” is one of those bits of running wisdom that get endlessly repeated but that still induce skepticism. How could it not matter if you get two instead of eight hours of sleep the night before a race? After all, you don’t see elites at Broadway shows or midnight movies the night before the New York City Marathon.

A new study supports the don’t-sweat-it conventional wisdom about sleep deprivation and performance. It also sheds light on why it feels natural to worry about bad pre-race sleep.

For the study, Dutch researchers had 10 men do all-out 20-minute cycling time trials under a few conditions. Before one of the time trials, the men arrived at the research lab at 11 p.m., and were not allowed to sleep (or even to lie down, for that matter) until they had completed the time trial at 1 p.m. the following afternoon.

Two of the time trials were done in the same atmospheric conditions (51 degrees Fahrenheit and 69% humidity), the only difference being that one of them was after the sleepless night. In the “normal” time trial, when the men had enjoyed a regular night’s sleep, they covered an average of 7.68 kilometers, or a little less than 5 miles, during their 20-minute cycling time trial. And they estimated their effort fairly accurately–the men guessed they’d covered 7.26 kilometers.

When riding after not sleeping, the men performed almost the same: they covered an average of 7.62 kilometers, and physiological measurements, including average heart rate, were also nearly identical.

What was significantly different was that after the sleep-deprived time trial, the men were way off in gauging their performance. They estimated that they had covered only 6.51 kilometers.

“The underestimation of the actual performance after sleep deprivation may lead to a decision not to start an activity in operational situations because of the feeling that the activity cannot be completed successfully,” the researchers wrote.

In other words, lack of sleep might make you a wimp, but once you get going, there’s every reason to believe you’ll race as well after one night of bad sleep as after good sleep. This is good news for the many marathoners whose nerves keep them up the night before. It’s also worth keeping in mind when race-day logistics require getting up much earlier than usual. You may think you’re not ready to roll, but you are.

In the video below, several elite marathoners discuss their pre-race sleep plan, which in many cases includes, yes, not panicking about bad sleep.