How long of a day can the Human Body tolerate?

Could the human body get used to, say, a 30 hour day? Instead of 8 hours a night you might sleep for 10, seeing as how we`re awake for an extra 4 hours.
Could we tolerate a 40 hour day? How long would it take to get acclimated?
If we ramped up the length of the days (like by 5 minutes per day) how far could we stretch it?

How long could this day be stretched before the body gives up?

For the sake of this question we`ll assume the same percentage of daylight verses night. Everything the same except the length of the day.
(I know if it happened along with our evolving then it would not be a problem. I am wondering about our bodies now, and the permanent sudden change in the length of a day.)

I know there`s lots of questions but I wanted to cover as much of the follow ups as I could in the first post.

2 summers ago, I was awake for 41 hours nonstop. I did not nap. For a variety of reasons, I was highly active, then sitting around in the car, then highly active at home, etc.

Caffeine played a part to a degree, but after a while it had no effect on me. I wasn’t going for some record, it just kind of worked out that way. By the end, I was not very aware of my surroundings, I had a ringing in my ears and generally was a mess. I slept for about 10 hours, and awoke needing more sleep.

I have read that in the military, air flight crews routinely train for a 24-hour mission during which time they are “On” at all times.


There’s really no way to answer that as little research has been done and there is huge variability of what makes up the workday for the “average” person. Are you a roofer working in Yuma, AZ in the Summer or an accountant? I’ve read about researchers working in caves who had no time reference and IIRC their wake/sleep cycle eventaully took longer than 24 hours but that doesn’t answer your question.

I have a personal record of 64 hours the last few days of freshman year of college, but I don’t think that that is what the OP was seeking. I have heard about people functioning–at increasingly degraded levels–for several days in a row.

On the other hand, quite a few years ago, a researcher took up residence in a cave (to avoid the influence of sunlight) and found that after a few weeks, her circadian rhythm had switched over to a 28 hour cycle. However, the data is still conflicting as the various studies reported on this page (CLICK the “Visit Site” button to see the reports) demonstrate.
One problem with drawing a conclusion based on a particular subject of a single experiment changing to a very long cycle is that we already know that people are quite variable. There are people who seem to need fewer than five hours of sleep each day and people who appear to need more than nine hours of sleep. How would those people fit into a radically altered schedule?

When I was in a college psychology class, we heard about a different caver who, after about a month, was staying awake for 24 hours and sleeping for 12. I’m sorry I don’t have a cite; I think it was a special educational production–not, for instance, an episode of NOVA. The guy decided to come up from the cave when a trap that he had set for a mouse–to catch it and make a friend of it–killed it instead.

Well, that gets us up to 36 hours anyway.

If we colonized a planet that had 40 hour day cycles could most people adapt?

During a 2 week period of preparing for exams, I found myself naturally drifiting into a 36 hours cycle (22 on, 14 off). I’ve never done it again because it played hell on my rhthyms and my health for the next month or so. My personal record is 56 hours awake before I finally went to a doc and got some sleeping pills.

But 36 hours seems almost the “natural” cycle for me if left alone.

One time visiting some friends on holiday, I was doing a 34 awake 14 sleep cycle for 6 days (3 “days”?) and I felt fine. Actually, I felt more awake and alert than I usually do, though I suppose I was on holiday. I think I could have carried on like that indefinitely (apart from the partying and all. :slight_smile: )