The Ideal Work Schedule, as Determined by Circadian Rhythms
Bron: Harvard Business Review
28 januari 2015
Humans have a well-defined internal clock that shapes our energy levels throughout the day: our circadian process, which is often referred to as a circadian rhythm because it tends to be very regular. If you’ve ever had jetlag, then you know how persistent circadian rhythms can be. This natural — and hardwired — ebb and flow in our ability to feel alert or sleepy has important implications for you and your employees.
Although managers expect their employees to be at their best at all hours of the workday, it’s an unrealistic expectation. Employees may want to be their best at all hours, but their natural circadian rhythms will not always align with this desire. On average, after the workday begins, employees take a few hours to reach their peak levels of alertness and energy — and that peak does not last long. Not long after lunch, those levels begin to decline, hitting a low at around 3pm. We often blame this on lunch, but in reality this is just a natural part of the circadian process. After the 3pm dip, alertness tends to increase again until hitting a second peak at approximately 6pm. Following this, alertness tends to then decline for the rest of the evening and throughout the early morning hours until hitting the very lowest point at approximately 3:30am. After hitting that all-time low, alertness tends to increase for the rest of the morning until hitting the first peak shortly after noon the next day. A very large body of research highlights this pattern, although of course there is individual variability around that pattern, which I’ll discuss shortly.
Managers who want to maximize their employees’ performance should consider this circadian rhythm when setting assignments, deadlines, and expectations. This requires taking a realistic view of human energy regulation, and appreciating the fact that the same employee will be more effective at some times of the day than others. Similarly, employees should take their own circadian rhythms into account when planning their own day. The most important tasks should be conducted when people are at or near their peaks in alertness (within an hour or so of noon and 6pm). The least important tasks should be scheduled for times in which alertness is lower (very early in the morning, around 3pm, and late at night).
Naps can be a good way to regulate energy as well, providing some short-term recovery that can increase alertness. A large body of evidence links naps to increases in task performance. However, even tired and sleep-deprived employees may find it difficult to nap if they work against their circadian rhythms. Fortunately, there is a nice complementary fit; naps are best scheduled for the low point of alertness in the circadian rhythm. Thus, smart managers and employees will schedule naps around 3pm, when they are less useful for important tasks anyway, such that they will be even more alert later on during the natural high points in their circadian rhythm.
Unfortunately, we often get this wrong. Many employees are flooded with writing and responding to emails throughout their entire morning, which takes them up through lunch. They return from lunch having already used up most of their first peak in alertness, and then begin important tasks requiring deep cognitive processing just as they start to move toward the 3pm dip in alertness and energy. We often put employees in a position where they must meet an end-of-workday deadline, so they persist in this important task throughout the 3pm dip. Then, as they are starting to approach the second peak of alertness, the typical workday ends. For workaholics, they may simply take a dinner break, which occupies some of their peak alertness time, and then work throughout the evening and night as their alertness and cognitive performance decline for the entire duration. And in the worst-case scenario, the employee burns the midnight oil and persists well into the worst circadian dip of the entire cycle, with bleary eyes straining just to stay awake while working on an important task at 3:30am. All of these examples represent common mismatches between an optimal strategy and what people actually do.
As I briefly noted above, there are of course individual differences in circadian rhythms. The typical pattern is indeed very common, and the general shape of the curve describes almost everyone. However, some people have a circadian rhythm that is shifted in one direction or the other. People referred to as “larks” (or morning people) tend to have peaks and troughs in alertness that are earlier than the average person, and “owls” (or night owls) are shifted in the opposite direction. Most people tend to experience such shifts across their lifetimes, such that they are larks as very young children, owls as adolescents, and then larks again as they become senior citizens. But beyond this pattern, people of any age can be larks or owls.
These differences in circadian rhythms (referred to as chronotypes) present some challenges and some benefits. The biggest challenge is matching patterns of activity to individual circadian rhythms. A lark working a late schedule or an owl working an early schedule is a chronotype mismatch that is difficult to deal with. Such employees suffer low alertness and energy, struggling to stay awake even if they really care about the task. Some of my own research indicates that circadian mismatches increase the prevalence of unethical behavior, simply because victims lack the energy to resist temptations. This is bad enough for an employee who is working alone. In the context of groups, finding a good time for a team composed of some larks and some owls to be at optimal effectiveness may be difficult. However, it does also provide opportunities. For organizations or tasks that require around-the-clock work, if managers can optimally match employees with different chronotypes to work different shifts, the work can be handed off among employees who are all working at or near their circadian peaks. This requires knowing the chronotype of each employee and using that information when developing work schedules.
Flextime provides an opportunity for employees to match their work schedules to their own circadian rhythms. However, managers often destroy this opportunity to capture value by punishing employees for using schedules that match an owl’s rhythm. In my own research, I found that supervisors tend to assume that employees who start and finish work late (versus early) are less conscientious and lower in performance, even if their behavior and performance is exactly the same as someone working an early riser’s schedule. Managers must see past their own biases if they want to optimize schedules in order to match the most important activities to the natural energy cycles of employees. Managers who do this will have energized, thriving employees rather than sleepy, droopy employees struggling to stay awake. Your most important tasks deserve employees who are working when they’re at their best.
Christopher M. Barnes is an assistant professor of management at the University of Washington’s Foster School of Business. He worked in the Fatigue Countermeasures branch of the Air Force Research Laboratory before pursuing his PhD in Organizational Behavior at Michigan State University.