What does it mean that energy follows ultradian rhythms?

Your energy cycles in 90-minute waves — work with these rhythms not against them.

Example: A software engineer notices she writes her best code in focused bursts that last about 90 minutes before her attention starts to fragment. She used to push through the fragmentation — forcing another 45 minutes of degraded work before finally breaking. After learning about ultradian rhythms, she restructures her day: 90 minutes of deep coding, then a 15-20 minute genuine break (walk, stretch, casual conversation — not email). She tracks her output for a month and discovers she produces more quality code in three 90-minute cycles with real breaks than she did in six hours of continuous desk time. The total clock hours are fewer. The total output is higher. The end-of-day exhaustion is lower. She did not become a better programmer. She became a better allocator of her existing capacity by working with her biology instead of against it.

Try this: Run a three-day ultradian tracking experiment. Set a gentle alarm for every 30 minutes during your workday. When it sounds, rate your current focus and energy on a 1-5 scale in a simple note or spreadsheet. Do not change your behavior — just observe and record. After three days, chart your ratings. You will see a wave pattern: peaks of 4-5 lasting roughly 60-100 minutes, troughs of 1-3 lasting 15-30 minutes. Mark the peaks and troughs. Now compare: during the troughs, were you pushing through demanding cognitive work? During the peaks, were you wasting capacity on low-value tasks like email or administrative sorting? Identify the two largest mismatches and redesign tomorrow's schedule to correct them — deep work during peaks, recovery and administrative tasks during troughs.