Fractional sleep: the method developed by sailors and military personnel

Sleep hygiene

They are sailors or military personnel, and they share a common practice: fractional sleep. Indeed, these athletes or professionals sometimes have to stay awake for several days, accumulating significant sleep debt. Knowing that it’s impossible not to sleep, what is the secret of these professionals to endure this sleep debt?

The consequences of sleep deprivation on the body and mind

Certain professions like military personnel and sailors often face sleep deprivation. To address this, they have developed very particular forms of sleep. By listening to their body’s rhythm, these atypical sleepers have learned to tame their bodies to stay awake even after long periods of wakefulness. During these extended wake periods, the body undergoes significant changes.

On a cognitive level, researchers from Nagoya University in Japan showed in 2010 that during sleep debt, the oxygenation of the frontal lobes of the cortex is affected. According to this study and many others, when sleep debt accumulates, the resulting disturbances can have serious consequences:

  • After 24 hours: Physiological changes are barely noticeable. There may be mood degradation or a decrease in muscle strength.
  • Beyond 30 hours: Symptoms become more significant. Visual disturbances may occur along with a decrease in alertness and short-term memory.
  • After 48 hours: The individual’s mental integrity is at stake. This syndrome, which sailors may experience, is synonymous with hallucinatory delirium. It’s not uncommon to hear sailors in long-distance races experiencing hallucinations, such as Michel Desjoyaux, who, alone on his boat, recounts handing over the helm to a teammate during a solo race.

A strict discipline is required for this type of sleep

When professional activity demands little or no sleep, the most effective tactic is to break up sleep rather than try to go without it, especially beyond 40 hours without sleep. To endure several weeks, sailors must abandon the so-called monophasic rhythm for a polyphasic sleep pattern. Fractional or polyphasic sleep is a resting mode where an individual divides their sleep into multiple nap phases throughout the day. As early as 2002, navigator Ellen McArthur was the first to track her waking and sleeping cycles in real-time during solo races, in order to identify periods conducive to effective sleep. When properly regulated, each sleep cycle allows for alternating phases of light sleep, deep sleep, and REM sleep, essential for physical and mental recovery.

At equivalent duration, the quality of fractional sleep will never match that of monophasic nocturnal sleep because humans are biologically programmed to sleep at night. Although restorative, polyphasic sleep should be reserved for limited periods as it can weaken immunity and lead to depression. When sleep deprivation is a constraint, only specific training and medical supervision can mitigate its consequences.