Hidden Rhythms Within Each Day


In this Wall Street Journal article, author Daniel Pink says that standard units of time – seconds, hours, weeks – “are really fences that our ancestors constructed to corral time. But one unit remains beyond our control: We inhabit a planet that turns on its axis at a steady speed in a regular pattern, exposing us to consistent periods of light and dark. The day is perhaps the most important way that we divide, configure, and evaluate our time.”

Research over the last 100 years has come to three conclusions about the impact of time of day on humans:

Each day, our cognitive abilities change in regular, predictable ways: a peak, a trough, and a rebound (about 20 percent of people have the reverse sequence).

People’s daily low point can be the equivalent of drinking the legal limit of alcohol.

We’re more and less effective at some tasks at different points in the daily cycle.

(To find out if you’re a night owl, take a day when you aren’t waking to an alarm clock and find the mid-point between bedtime and waking up. If it’s 5:30 a.m. or later, you’re an owl.)

• The peak – During this part of the day, our executive functioning and concentration are at their best. For 80 percent of people, sharp-minded analytical capacities crest in the late morning, so that’s when it’s smart to do work that requires heads-down concentration and brain power.

• The trough – Executive functioning plummets during the afternoon. One study found that in hospitals, harmful errors with anesthesia were three times more likely to occur after 3 p.m. Another study in Denmark found that students who were randomly assigned to take tests in the afternoon performed at a level equivalent to having missed two weeks of school. (Interestingly, if students had a 20-30-minute break to eat, play, and chat before the test, they scored higher than morning test takers.) Early afternoon is the part of the day when it’s best to do routine administrative work – answering e-mail, filing papers.

• The rebound – For most people, this is the late afternoon and early evening. It’s the best time to be creative, engaging in activities that have non-obvious, surprising outcomes. “In the late afternoons and early evenings,” says Pink, “most people are somewhat less vigilant than during the peak, but more alert and in a better mood than during the trough. That combination has advantages. A boosted mood leads to greater openness. A slight reduction in vigilance lets in a few distractions – but those distractions can help us spot connections that we might have missed when our filters were tighter.” This is a time for brainstorming and creative thinking. (For night owls, this is in the morning.)

The implication of these findings is that we should tune in to our unique body rhythms and, if possible, synchronize activities to the optimal time of day. What about exercise? If the goal is to lose weight or boost mood for the rest of the day, Pink says morning workouts are best. To avoid injury, afternoon or evening workouts are optimal. What about breaks from work? It turns out that frequent, short breaks are best, especially if they involve moving around – for example, a five-minute walk every hour. Breaks are even more beneficial when they’re taken outdoors, with colleagues, and our minds are completely off work.


“How to Be Healthier, Happier, and More Productive: It’s All in the Timing” by Daniel Pink in The Wall Street Journal, December 29, 2017, http://on.wsj.com/2Edo3oF; Pink’s book is When: The Scientific Secrets of Perfect Timing (Riverhead Books, 2018).


Marshall Memo 718 January 8, 2018