The 45-minute nap.

A 45-minute nap is deep enough to give you a meaningful chunk of slow-wave N3 sleep — the stage responsible for physical recovery, glymphatic clearance (the brain's waste removal system), and growth hormone release. For someone with a high physical training load or real sleep debt, a 45-minute nap delivers actual physiological recovery, not just alertness. The catch is the same as a 30-minute nap: you are very likely still in N3 when the alarm goes off, which means 15–30 minutes of sleep inertia on wake. The difference is that at 45 minutes you have gotten enough benefit that the inertia is a worthwhile trade — whereas at 30 minutes you get the inertia without enough benefit to justify it. Who should use a 45-minute nap? Athletes in two-a-day training, night-shift workers bridging between shifts, parents of newborns catching recovery sleep, and anyone who has accumulated 3+ hours of nighttime sleep debt and needs to drive or perform mental work later but not *immediately*. Practical execution: set an alarm, but build in 20 minutes of "recovery buffer" before any cognitively demanding task. Plan to use the grogginess window to do something low-stakes — shower, walk, eat — then expect cognitive performance to rebound and exceed pre-nap baseline for several hours.