“Human beings aren’t designed to expend energy continuously. Rather, we’re meant to pulse between spending and recovering energy.”
– Tony Schwartz (source)
In the late 1950’s, researchers William Dement and Nathaniel Kleitman documented that humans sleep in 90-minute cycles – from light to deep sleep and back to light sleep again. Professor Kleitman later discovered that a similar pattern happens when we are awake – from a state of alertness to physiological fatigue. After 90 minutes of work, we start to feel tired and less productive. Essentially, this is our bodies telling us that we need to slow down and take a break.
Unfortunately, we often ignore these biological signals and try to mask the impact with stimulants like caffeine and sugar. When we’re on a tight deadline or under lots of pressure, we might also summon up the stress hormones adrenaline and cortisol. These stimulants work in the short term but they usually lead to an inevitable feeling of crashing.
Research by Professor K. Anders Ericsson on elite performers reinforced the 90-minute cycle. Professor Ericsson found the best violinists daily practice usually consisted of three sessions of 90 minutes each with breaks for recuperating between each session. These elite musicians rarely worked for more than 4.5 hours per day and they slept almost an hour more than average musicians. A similar pattern emerged in studies of athletes, actors, and chess players.
More from Professor Ericsson:
To maximize gains from long-term practice, individuals must avoid exhaustion and must limit practice to an amount from which they can completely recover on a daily or weekly basis.
I call this effect the 90-minute rule and recommend applying it to your daily routine, regardless of your profession. You should schedule your day in 90-minute periods of intense, uninterrupted work with 20-30 minutes of renewal breaks between them. You should also make sure business meeting don’t last longer than 90 minutes. When you plan an offsite or a conference agenda, no session or presentation should be longer than 90 minutes or else you risk losing the audience.
Adhering to the 90-minute rule takes discipline, especially since we live in an always-on society. But the science tells us we can be better performers if we give ourselves enough time to recuperate. Take a walk, eat a healthy snack, or even chit-chat with co-workers.
And the next time your boss asks if you’re goofing off at work, refer to the 90-minute rule and say you’re taking a science-mandated break.
[…] Limit the length of learning sessions. All-night cramming is inefficient because attention spans are limited and we retain decreasing amounts of information over time. I recommend no more than 90-minute sessions (read the 90-minute rule). […]