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Written by:  Daniel Pink is the author of When: The Scientific Secrets of Perfect Timing, from which this article is adapted.

It’s a cloudy Tuesday in Ann Arbor, Michigan, and for probably only time in my life, I’m wearing hospital greens and scrubbing in for surgery. Beside me is Dr. Kevin Tremper, an anesthesiologist and professor of the University of Michigan Medical School’s Department of Anesthesiology.

“Each year, we put 90,000 people to sleep and wake them up,” he tells me. “We paralyze them and start cutting them open.” Tremper oversees 150 physicians and another 150 medical residents who wield these magical powers. In 2010 he changed how they do their jobs.

Flat on the operating room table is a twenty-something man with a smashed jaw. On a nearby wall is a large-screen television with the names of the five other people in hospital greens—nurses, physicians, a technician—who surround the table. At the top of the screen is the patient’s name. The surgeon, an intense man in his thirties is itching to begin. But before anybody does anything, they call a time-out. Almost imperceptibly, each person takes one step backward. Then, looking at either the big screen or a wallet-size plastic card hanging from their waists, they introduce themselves to one another by first name and proceed through a nine-step “Pre-Induction Verification” checklist that ensures they’ve got the right patient, know his condition and any allergies, understand the medications the anesthesiologist will use, and have any special equipment they might need. When everyone is finished and all the questions are answered—the whole process takes about three minutes—the time-out ends and the young anesthesia resident begins to put the patient, already partly sedated, fully to sleep. Soon the patient is out, his vital signs are stable, and the surgery can begin.

Then the team steps back from the operating table once again. Each person reviews the steps on the “Pre-Incision Time-Out” card to make sure everyone is prepared. They regain their individual and collective focus. And only then does everyone step back to the operating table and the surgeon begins repairing the jaw.

I call time-outs like these “vigilance breaks,” brief pauses before high-stakes encounters to review instructions and guard against error. Tremper says that in the time since he implemented these breaks at the hospital, the quality of care has risen, complications have declined, and both doctors and patients are more at ease.

Afternoons are the Bermuda Triangles of our days. Across many domains, the trough represents a danger zone for productivity, ethics, and health. Anesthesia is one example. Researchers at Duke Medical Center reviewed about 90,000 surgeries at the hospital and identified what they called “anesthetic adverse events”— either mistakes anesthesiologists made, harm they caused to patients, or both. Adverse events were significantly “more frequent for cases starting during the 3 p.m. and 4 p.m. hours.” The probability of a problem at 9 a.m. was about 1 percent. At 4 p.m., 4.2 percent. In other words, the chance of something going awry was four times greater during the trough than during the peak. On actual harm (not only a slip up but also something that hurts the patient), the probability at 8 a.m. was 0.3 percent — three-tenths of one percent. But at 3 p.m., the probability was 1 percent — one in every one hundred cases, a threefold increase. Afternoon circadian lows, the researchers concluded, impair physician vigilance and “affect human performance of complex tasks such as those required in anesthesia care.”

Or consider colonoscopies. One oft-cited study of more than 1,000 colonoscopies found that endoscopists are less likely to detect polyps — small growths on the colon — as the day progresses. Every hour that passed resulted in a nearly 5 percent reduction in polyp detection. Some of the specific morning vs. afternoon differences were stark. For instance, at 11 a.m., doctors found an average of more than 1.1 polyps in every exam. By 2 p.m., though, they were detecting barely half that number even though afternoon patients were no different from the morning ones.

What’s more, other research has shown that doctors are significantly less likely even to fully complete a colonoscopy when they perform it in the afternoon.

We expect important encounters with experienced professionals like physicians to turn on who is the patient and what is the problem. But many outcomes depend even more forcefully on when is the appointment.

What’s going on is a decline in vigilance. In 2015 Hengchen Dai, Katherine Milkman, David Hoffman, and Bradley Staats led a massive study of handwashing at nearly three dozen U.S. hospitals. Using data from sanitizer dispensers equipped with radio frequency identification (RFID) to communicate with RFID chips on employee badges, researchers monitored who washed their hands and who didn’t. They studied more than 4,000 caregivers (two-thirds of whom were nurses), who over the course of the research had nearly 14 million “hand hygiene opportunities.” The results were not pretty. On average, these employees washed their hands less than half the time when they had an opportunity and a professional obligation to do so. Worse, the caregivers, most of whom began their shifts in the morning, were even less likely to sanitize their hands in the afternoons. This decline from the relative diligence of the mornings to the relative neglect of the afternoon was as great as 38 percent.

The consequences are grave. “The decrease in hand hygiene compliance that we detected during a typical work shift would contribute to approximately 7,500 unnecessary infections per year at an annual cost of approximately $150 million across the 34 hospitals included in this study,” the authors write. Spread this rate across annual hospital admissions in the U.S., and the cost of the trough is massive: 600,000 unnecessary infections, $12.5 billion in added costs, and up to 35,000 unnecessary deaths.

Afternoons can also be deadly beyond the white walls of a hospital. In the United Kingdom, sleep-related vehicle accidents peak twice during every twenty-four-hour period. One is between 2 a.m. and 6 a.m., the middle of the night. The other is between 2 p.m. and 4 p.m., the middle of the afternoon. Researchers have found the same pattern of traffic accidents in the U.S., Israel, Finland, France, and other countries.

The good news is that vigilance breaks can loosen the trough’s grip on our behavior. As the doctors at the University of Michigan demonstrate, inserting regular mandatory vigilance breaks into tasks helps us regain the focus needed to proceed with challenging work that must be done in the afternoon.

This simple intervention is backed by heartening evidence. For instance, the largest health care system in the U.S. is the Veterans Health Administration, which operates about 170 hospitals across the country. In response to the persistence of medical errors (many of which occurred in afternoons), a team of physicians at the VA implemented a comprehensive training system across the hospitals (on which Michigan modeled its own efforts) that was built around the concept of more intentional and more frequent breaks, and featured such tools as “laminated checklist cards, whiteboards, paper forms, and wall mounted posters.” One year after the training began, the surgical mortality rate (how often people died during or shortly after surgery) dropped 18 percent.

Still, for most people, work doesn’t involve paralyzing others and cutting them open. For the rest of us, another type of break offers a simple way to steer around the dangers of the trough. Call them “restorative breaks.”

From the schoolhouse to the courthouse: The Power of restorative breaks

Schoolchildren in Denmark who take standardized tests in the afternoon score significantly worse than those who take the exams earlier in the day. To a school principal or education policy maker, the response seems obvious: Move all the tests to the morning. However, the researchers also discovered another remedy, one with applications well beyond schools and tests, which is remarkably easy to explain and implement.

When the Danish students had a twenty-to-thirty-minute break “to eat, play, and chat” before a test, their scores did not decline. In fact, they increased. As the researchers note, “a break causes an improvement that is larger than the hourly deterioration.” That is, scores go down after noon. But scores go up by a higher amount after breaks.

Taking a test in the afternoon without a break produces scores that are equivalent to spending less time in school each year and having parents with lower incomes and less education. But taking the same test after a twenty-to-thirty-minute break leads to scores that are equivalent to students spending three additional weeks in the classroom and having somewhat wealthier and better-educated parents. And the benefits were the greatest for the lowest-performing students.

Like many schools, Danish schools offer only two breaks each day. Worse, legions of school systems are cutting back on recess and other restorative pauses for students in the name of rigor and—get ready for the irony—higher test scores. But as Harvard’s Francesca Gino, one of the study’s authors, puts it, “If there were a break after every hour, test scores would actually improve over the course of the day.”

“We believe these results to have two important policy implications,” say the researchers who studied the Danish experience. “[F]irst, cognitive fatigue should be taken into consideration when deciding on the length of the school day and the frequency and duration of breaks. Our results show that longer school days can be justified, if they include an appropriate number of breaks. Second, school accountability systems should control for the influence of external factors on test scores . . . a more straightforward approach would be to plan tests as closely after breaks as possible.”

Perhaps it makes sense that a cup of apple juice and a few minutes to run around works wonders for eight-year-olds solving arithmetic problems. But restorative breaks have a similar power for adults with weightier responsibilities.

In Israel, two judicial boards process about 40 percent of the country’s parole requests. At their helm are individual judges whose job is to hear prisoners’ cases and make decisions about their fate. Judges aspire to be rational, deliberative, and wise, but judges are also human beings subject to the same daily rhythms as the rest of us. In 2011 three social scientists (two Israelis and one American) used data from these two parole boards to examine judicial decision-making. They found that, in general, judges were more likely to issue a favorable ruling—granting the prisoner parole or allowing him to remove an ankle monitor—in the morning than in the afternoon. (The study controlled for the type of prisoner, the severity of the offense, and other factors.) But the pattern of decision-making was more complicated, and more intriguing, than a simple a.m./p.m. divide.

The following chart shows what happened. Early in the day, judges ruled in favor of prisoners about 65 percent of the time. But as the morning wore on, that rate declined. And by late morning, their favorable rulings dropped to nearly zero. So a prisoner slotted for a 9 a.m. hearing was likely to get parole while one slotted for 11:45 a.m. had essentially no chance at all—regardless of the facts of the case.

But look what happens after the judges take a break. Immediately after that first break, for lunch, they become more forgiving— more willing to deviate from the default—only to sink into a more hardline attitude after a few hours. But look what occurs when those judges then get a second break. They return to the same rate of favorable decisions they displayed first thing in the morning.

So if you happen to appear before a parole board just before a break rather than just after one, you’ll likely spend a few more years in jail—not because of the facts of the case but because of the time of day. The researchers say they cannot identify precisely what’s driving this phenomenon. It could be that eating restored glucose levels and replenished the judges’ mental reserves. It could be that a little time away from the bench lifted their mood. It could be that the judges were tired and that rest reduced their fatigue.

Whatever the explanation, a factor that should have been extraneous to judicial decision-making and irrelevant to justice itself—whether and when a judge took a break—was critical. And the wider phenomenon—that breaks can often mitigate the trough—likely applies “in other important sequential decisions or judgments, such as legislative decisions . . . financial decisions, and university admissions decisions.”

So if the trough is the poison and restorative breaks are the anti- dote, what should those breaks look like? There’s no single answer, but science offers five guiding principles.

1. Something beats nothing.

One problem with afternoons is that if we stick with a task too long, we lose sight of the goal we’re trying to achieve, a process known as “habituation.” Short breaks from a task can prevent habituation, help us maintain focus, and reactivate our commitment. And frequent short breaks are more effective than occasional ones. DeskTime, a company that makes productivity tracking software, says that “what the most productive 10% of our users have in common is their ability to take effective breaks.” Specifically, after analyzing its own data, DeskTime claims to have discovered a golden ratio of work and rest. High performers, its research concludes, work for fifty-two minutes and then break for seventeen minutes. (DeskTime never published the data in a peer-reviewed journal, so your mileage may vary. But the evidence is overwhelming that even short breaks are effective.)

2. Moving beats stationary.

Sitting, we’ve been told, is the new smoking—a clear and present danger to our health. But it also leaves us more susceptible to the dangers of the trough, which is why simply standing up and walking around for five minutes every hour during the workday can be remarkably potent. One study showed that hourly five-minute walking breaks boosted energy levels, sharpened focus, and “improved mood throughout the day and reduced feelings of fatigue in the late afternoon.” These “microbursts of activity,” as the researchers call them, were also more effective than a single thirty-minute walking break—so much so that the researchers suggest that organizations “introduce physically active breaks during the workday routine.”

3. Social beats solo.

Time alone can be replenishing, especially for introverts. But much of the research on restorative breaks points toward the greater power of being with others, particularly when we’re free to choose with whom we spend the time. In high-stress occupations like nursing, social and collective rest breaks not only minimize physical strain and cut down on medical errors, they also reduce turnover; nurses who take these sorts of breaks are more likely to stay at their jobs. Likewise, research in South Korean workplaces shows that social breaks—talking with coworkers about something other than work—are more effective at reducing stress and improving mood than either cognitive breaks (answering e-mail) or nutrition breaks (getting a snack).

4. Outside beats inside.

Nature breaks may replenish us the most. Being close to trees, plants, rivers, and streams is a powerful mental restorative, one whose potency most of us don’t appreciate. For example, people who take short walks outdoors as breaks return with better moods and greater replenishment than people who walk indoors. Even taking a break indoors amid plants is better than doing so in a green-free zone.

5. Fully detached beats semidetached.

By now, it’s well-known that 99 percent of us cannot multitask. Yet when we take a break, we often try to combine it with another cognitively demanding activity—perhaps checking our text messages or talking to a colleague about a work issue. That’s a mistake. In one South Korean study, relaxation breaks (stretching or daydreaming) eased stress and boosted mood in a way that multitasking breaks did not. Tech-free breaks also “increase vigor and reduce emotional exhaustion.” Or as other researchers put it: “Psychological detachment from work, in addition to physical detachment, is crucial, as continuing to think about job demands during breaks may result in strain.”