Ultradian cycles

Ultradian cycles are roughly 90-minute rhythms that occur during sleep and waking, shaping cycles of sleep stages and periods of focus and performance. 1

• Difference from circadian rhythms: Circadian rhythms run on an approximately 24-hour cycle; ultradian rhythms are shorter and recur throughout the day. 2
• Work, learning, and activity: A focused bout of work, learning, or physical activity can be organized in a block of about 90 minutes or less. The work cycle can be started deliberately, though intense focus may take time to build. 3
• Focus and neurochemicals: The first five to ten minutes may be a warm-up; focus tends to diminish after roughly 90 minutes as the capacity to release acetylcholine and dopamine drops. 4