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Ultradian Rhythms

Your brain naturally cycles every 90-120 minutes. Fight it or flow with it.

What Are Ultradian Rhythms?

While circadian rhythms are your 24-hour cycle, ultradian rhythms are shorter cycles within the day. The most relevant for work is the Basic Rest-Activity Cycle (BRAC) — approximately 90-120 minute periods of high and low alertness.

You experience this cycle at night as sleep stages. During the day, it manifests as waves of focus and fatigue.

Elite performers from athletes to musicians typically practice in 90-minute sessions. This isn't coincidence — it aligns with how your brain naturally operates.

The 90-Minute Focus Cycle

Minutes 0-20 — Warmup, getting into focus
Minutes 20-70 — Peak focus zone
Minutes 70-90 — Focus declining, diminishing returns
After 90 — Rest period needed (15-20 minutes)

Pushing past 90 minutes without a break is fighting biology. You might work, but quality suffers.

Signs Your Cycle Is Ending

Yawning or sighing
Mind wandering more frequently
Craving food, coffee, or distraction
Difficulty maintaining focus
Reading the same sentence multiple times

These aren't failures — they're your brain signaling it's time for renewal.

Working With Your Rhythms

Plan 90-minute focus blocks — One cycle, one major task
Take real breaks between — 15-20 minutes of non-work
Don't fight the dip — When focus drops, take a break
Aim for 4-5 cycles per day — More isn't always better

Ultradian vs. Pomodoro

The Pomodoro Technique uses 25-minute work periods. Ultradian cycles suggest 90-minute periods. Which is better?

Pomodoro: Better for tasks requiring willpower, avoiding procrastination
90-minute blocks: Better for deep work requiring extended focus
You can nest Pomodoros inside an ultradian cycle: 3 Pomodoros + longer break

Both work. The key is regular breaks, regardless of the interval you choose.