It took some time for their sleep to regulate but by the fourth week a distinct two-phase sleep pattern emerged. They slept first for four hours, then woke for one to three hours before falling into a second four-hour sleep. This finding suggests bi-phasic sleep is a natural process with a biological basis.
Pros and cons
Today’s society often doesn’t allow for this type of flexibility, thus we have to conform to today’s sleep/wake schedules. It is generally thought a continuous seven to nine-hour unbroken sleep is probably best for feeling refreshed. Such a schedule may not suit our circadian rhythms however, as we desynchronise with the external 24-hour light/dark cycle.
To successfully maintain a split sleep schedule, you have to get the timing right – that is commencing sleep when there is a strong drive for sleep and during a low circadian point in order to fall asleep quickly and maintain sleep.
Some of the key advantages of a split sleep schedule include the flexibility it allows with work and family time (where this flexibility is afforded). Some individuals in modern society have adopted this type of schedule as it provides two periods of increased activity, creativity and alertness across the day, rather than having a long wake period where sleepiness builds up across the day and productivity wanes.
In support of this, there is growing evidence suggesting naps can have important benefits for memory and learning, increasing our alertness and improving mood states. Some believe sleep disorders, like sleep maintenance insomnia, are rooted in the body’s natural preference for split sleep. Therefore, split sleep schedules may be a more natural rhythm for some people.
Implications for shift work
Split sleep schedules have recently begun to emerge as a potential alternative to continuous night shift work. Working at night has the combined problems of prolonged wakefulness (often working eight to 12 hour shifts) and circadian misalignment (working at a time of night when you would normally be asleep). Shift workers frequently complain of fatigue and reduced productivity at work and they are at increased risk for chronic disease such as obesity, type 2 diabetes and heart disease.
Some industries have employed schedules with shorter, but more frequent sleep opportunities on the premise that the drive for sleep will be less with reduced time. For example, six hours on/six hours off, four hours on/eight hours off, and eight hours on/eight hours off, limit time on shift and reduce extended periods of wakefulness. Split sleep/work schedules divide the day into multiple work/rest cycles so employees work multiple short shifts, broken up with short off-duty periods every 24 hours.
Split-shift schedules that maintain adequate sleep time per 24 hours may be beneficial for sleep, performance and safety. A number of recent studies have found split sleep provides comparable benefits for performance to one big sleep, if the total sleep time per 24 hours was maintained (at around seven to eight hours total sleep time per 24 hours).
However, as might be expected, performance and safety can still be impaired if wake up and start work times are in the early hours of the morning. And we don’t know if these schedules afford any benefits for health and reduce the risk for chronic disease.
While the challenges of night shift work cannot be eliminated, the advantage of some split shift schedules is that all workers get at least some opportunity to sleep at night and do not have to sustain alertness for longer than six to eight hours.
Although we aspire to have consolidated sleep, this may not suit everyone’s body clock or work schedule. It might in fact be a throwback to a bi-model sleep pattern from our pre-industrial ancestors and perhaps work well in a modern industrial setting.
Melinda Jackson - Senior Research Fellow in the School of Health and Biomedical Sciences, RMIT University
Siobhan Banks - Senior Research Fellow, Centre for Sleep Research, University of South Australia
Originally published on The Conversation.