Every person needs a certain amount of sleep to function optimally. The vast majority of adults have a sleep need for optimal performance (SNOP) of 7-9 hours, although there are individuals who need significantly less — known as “short-sleepers” — and some people who need more. SNOP is largely determined by genetics, but can also be affected by lifestyle factors like the amount and intensity of physical activity.
The reason we have coined the term SNOP, as opposed to just referring to “sleep need,” is that the amount of sleep a person needs depends on what their goal is. If a person wants to perform at their absolute best, they need to sleep as much as possible. A person’s SNOP is actually the maximum amount s/he can sleep consistently. However, if a person is satisfied with 90% performance, they may be able to sleep significantly less per night. Many people are willing to make this tradeoff.
The Ideal Way (in theory) to Determine SNOP: Extended Sleep for a few days
The only way for a person to definitely determine his/her SNOP is to sleep as much as possible for several nights and see where sleep starts leveling off. Figure 1 below shows the results of an experiment in which people were given an opportunity to sleep 12 hours per night for 9 days. On the first night of the experiment, E1, the average sleep was about 10.6 hours, and it decreased each night thereafter, leveling off at around 8.4 hours with a range of 7.29–9.26 hours. It isn’t necessary to sleep as much as possible for 9 nights to determine sleep SNOP to a very high degree of accuracy. After about 4 nights, fitting an exponential curve to the data will give a fairly accurate measure.
The challenge with this method is that it is very difficult for people to create the right environment to actually sleep as much as possible.
A More Practical Method for Estimating Sleep Need: Sleep Rebound
Sleeping as much as possible for four or more days to determine SNOP is often impractical. Luckily, there are ways to estimate SNOP more easily. Sleep rebound is the difference between the amount of sleep obtained on the first night of sleeping as much as possible and the person’s habitual sleep, i.e. their average sleep. Figure 2 shows the correlation between sleep rebound and a person’s average sleep deficit, i.e. on average how much less they sleep than their SNOP each night (the paper called this potential sleep debt).
Although most people don’t sleep as much as they possibly could on weekends, many people sleep a lot more on weekends than during the week. By looking at the rebound between weekend nights and weekday nights, we can estimate sleep need. This estimate can be made using either objective sleep data, or using self-reported sleep data during the week and on weekends.