Break up intense intellectual work into focus blocks of a maximum of 90 minutes to respect the brain's natural attention rhythms.

noli's read

This method is inspired by the basic rest-activity cycle theorized by researcher Nathaniel Kleitman, which suggests that our level of alertness naturally fluctuates every 90 minutes (expert opinion). Observational studies on deliberate practice conducted by researcher Anders Ericsson show that high-level experts indeed spontaneously limit their sessions of maximum effort to this duration. Furthermore, experimental work (such as that of Escera and Grau, 1994) confirms the existence of rhythmic fluctuations in our selective attention. However, the idea of a strict, universal biological 90-minute barrier should be qualified. An experimental study conducted by Neubauer and Freudenthaler in 1995 on attention did not detect a fixed 90-minute cognitive rhythm, revealing that cycles vary greatly depending on the individual, their motivation, and the nature of the task. Finally, the explanation linking this drop in performance to the sudden depletion of acetylcholine and dopamine precisely at the 90-minute mark relies on theoretical extrapolations and lacks direct human clinical trials (RCT) in work conditions.

the sources

1. 1NIH Office of Dietary Supplements 2026
2. 2Manson JE et al. 2019
3. 3Bhatt DL et al. 2019
4. 4Khan SU, Lone AN, Khan MS, et al. 2021
5. 5Liao Y, Xie B, Zhang H, et al. 2019
6. 6hubermanprotocols.com (fan reference guide)