What is Ultradian Rhythm?
Ultradian rhythms are biological cycles that repeat more than once per 24 hours. Examples include the 90-minute sleep cycle, the 90–120 minute basic rest-activity cycle (BRAC), and shorter attention cycles.
Key Cycles
- •90-minute cycle — deep work, creative flow
- •20-minute cycle — short breaks, recovery
- •Neurotransmitter depletion — focus depletes; rest restores
Why does Ultradian Rhythm matter?
Ultradian rhythms matter because many body processes repeat more than once a day rather than following a single 24-hour cycle. The clearest example is sleep, which cycles between non-REM and REM stages several times each night, each cycle lasting roughly 90 minutes on average.
Hormone release also tends to be pulsatile. Cortisol, growth hormone, and reproductive hormones are secreted in bursts, and this pulse pattern can affect how target tissues respond to them.
What affects Ultradian Rhythm?
Ultradian rhythms are shaped by brain circuits, hormones, age and the timing of sleep. Sleep-cycle length and structure change across the lifespan, and sleep deprivation, alcohol and some medications can alter the balance of REM and deep sleep.
The idea of a daytime "basic rest-activity cycle" of about 90 minutes, proposed by Nathaniel Kleitman, remains debated; evidence for a consistent waking cycle of attention is weaker than for sleep cycles. Individual rhythms also vary considerably from person to person.
In ONDA Life
Part 8 "Ultradian Optimization" works within natural rhythms (90/20-minute cycles) for the timely restoration of neurotransmitters. Working against these rhythms leads to cognitive burnout; working with them supports neural resilience.