What are ultradian cycles?

Ultradian cycles, also known as ultradian rhythms, are cycles that occur throughout the day and are shorter than 24-hour circadian rhythms. These rhythms generally last about 90 minutes and govern our ability to focus and engage in tasks, both during sleep and wakefulness.

In sleep, for example, our sleep cycles are organized into these 90-minute segments, alternating between different sleep phases such as lighter sleep (stages 1 and 2) and deeper sleep (stages 3 and 4) [1].

During wakefulness, ultradian rhythms also play a crucial role. Our ability to focus and perform physically or mentally peaks during these 90-minute cycles. After about 90 minutes, there is typically a significant drop in our ability to concentrate or engage physically, which is why it's often recommended to limit intense work or learning sessions to 90 minutes or less [2].

These cycles are linked to the function of neurotransmitters like acetylcholine and dopamine, which promote focus and motivation. As the 90-minute cycle concludes, the release of these neurochemicals diminishes, reducing our capacity to maintain high levels of focus [3].