For most of human history, people did not sleep in one unbroken eight-hour block. They slept in two. And the hour of quiet wakefulness between those two phases was treated as normal — even productive — rather than as a symptom of insomnia. That history has significant implications for how athletes structure their recovery.
Historian Roger Ekirch's landmark 2001 research, expanded in his 2005 book "At Day's Close," compiled hundreds of references from pre-industrial European literature, court records, and personal diaries describing a "first sleep" and "second sleep" separated by approximately 60–90 minutes of wakefulness around midnight. People used this waking interval for quiet reflection, prayer, conversation, or light activity before returning to sleep for the second phase until dawn.
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This pattern only disappeared after the Industrial Revolution, when artificial lighting extended social and work life into the evening and compressed natural sleep into a single later block. But the biological signature of biphasic sleep architecture may still be present in modern humans, emerging as the body's natural default when removed from artificial light schedules.
Chronobiologist Thomas Wehr's famous 1992 study at the National Institute of Mental Health placed healthy volunteers on a shortened light exposure schedule — 14 hours of darkness per day for a month. Within three weeks, the majority spontaneously transitioned to a biphasic sleep pattern: two 3.5–4 hour sleep periods separated by 1–2 hours of calm wakefulness. Crucially, this waking interval was characterised by dramatically elevated prolactin — a hormone associated with deep calm, tranquillity, and cellular repair — levels that are not typically seen during waking hours.
For athletes, this is pharmacologically interesting. Prolactin surges during sleep and during very specific states of relaxed wakefulness. The nocturnal prolactin profile in biphasic sleepers appears to include an additional elevation during the inter-sleep interval — a phenomenon Wehr's team documented and that may contribute to a broader hormonal restoration profile than consolidated monosleep provides.
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Modern evidence from sleep architecture research suggests the boundary between the two sleep phases in natural biphasic sleepers often falls at the transition between the first and second complete 90-minute ultradian sleep cycle. This is the point at which N3 slow-wave sleep peaks and then begins to taper, and REM sleep becomes progressively more dominant. The natural arousal point at the end of the first sleep phase corresponds to a biologically light moment — easier to wake from, less associated with sleep inertia, and hormonally distinct.
For athletes who experience spontaneous waking around 1–3 AM without distress, the evidence suggests this may be a healthy circadian variant rather than a pathological disruption. Treating it as insomnia — lying in bed anxious about not sleeping — is physiologically counterproductive. Wehr's subjects who accepted and used the waking interval calmly returned to sleep efficiently and reported high subjective sleep quality.
Practical implications diverge somewhat from the historical model, however. The biphasic pattern Ekirch documented was shaped by sunset-to-sunrise scheduling — first sleep at 9–10 PM, waking at midnight, second sleep from 1–2 AM to 6–7 AM. Modern athletes with evening training sessions and artificial lighting will have their first sleep phase delayed to 11 PM–midnight, compressing the architecture significantly. Attempting to force biphasic sleep onto a modern schedule risks total sleep time reduction rather than quality improvement.
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Where the biphasic model has the clearest application for modern athletes is in the afternoon nap as a culturally sanctioned second sleep period. Mediterranean and Latin American cultures have historically maintained a midday biphasic rest — the siesta — which aligns with the post-lunch circadian dip in alertness documented in chronobiology. A 20–30 minute nap at 1–3 PM captures N2 sleep without entering slow-wave sleep, avoiding sleep inertia while restoring alertness and supporting motor pattern consolidation.
Athletes in double-training-session environments — morning and afternoon sessions — are the strongest candidates for using a structured midday rest as a functional second sleep phase, even if unconnected to any nocturnal biphasic pattern.
The timing and quality of your sleep architecture shapes the hormonal restoration available during recovery. The free tool at winsport.uk/tools/health/sleep-cycle-calculator helps you map your sleep cycles — including the timing of N3 and REM phases — so you can understand whether adjusting sleep timing or introducing a scheduled nap might improve the recovery quality your training load requires.
Have you ever woken spontaneously at 1–2 AM, felt calm rather than anxious, and then returned to sleep naturally? That might not be insomnia — it might be your ancestral sleep architecture reasserting itself.