
Activity Does Not Always Equal Productivity - indus
http://dealbook.nytimes.com/2013/10/11/activity-does-not-always-equal-productivity/?_r=0
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jere
>Human beings are designed to operate in 90-minute cycles. At night, we move
through the five stages of sleep in that time — the Basic Rest Activity Cycle.
During the day, we are guided by our ultradian rhythms, and we move from high
physiological alertness toward physiological fatigue in 90-minute intervals.

I was in the comments here the other day defending the use of words like
"design" and "purpose" to describe evolution. But even for me, this sets off
my bullshit detector.

I would accept the sleep thing, though a precise 90 minutes is a stretch: "In
humans, the average length of the first sleep cycle is approximately 90
minutes and 100 to 120 minutes from the second to the fourth cycle, which is
usually the last one."
[http://en.wikipedia.org/wiki/Sleep#Physiology](http://en.wikipedia.org/wiki/Sleep#Physiology)

But does anyone have a citation for that kind of cycle during the day?

~~~
RollAHardSix
Somewhat related to what your asking, but according to a rather famous study
done by KA Ericsson on Deliberate Practice and it's effect of learning, the
optimal learning (for violinists and I've seen similar results when applied to
my Mixed Martial Artists) is 90 minutes of deliberate activity, a short break,
90 minutes of further deliberate practice, followed by a second break, by
another 90 minutes of deliberate practice. (Time for training sessions is of
course the enemy, and practice is deliberate enough to cause mental and
physical fatigue).

Source:
[http://graphics8.nytimes.com/images/blogs/freakonomics/pdf/D...](http://graphics8.nytimes.com/images/blogs/freakonomics/pdf/DeliberatePractice\(PsychologicalReview\).pdf)

