Measuring HRV during sleep is crucial because it acts as a "blank canvas," removing the confounding variables of daily psychological and physiological stress. This provides the most accurate window into the nervous system's underlying ability to repair and regulate itself. You cannot fake regulation during sleep.

Insomnia is often maintained by 'conditioned arousal,' where your brain learns to associate your bed with being awake (from working, watching TV, or worrying in it). To break this, if you're awake for 20 minutes, get out of bed until you're sleepy again to re-teach your brain that bed is only for sleep.

Bryan Johnson suggests focusing on a single metric: pre-sleep resting heart rate. Lowering it through specific habits (like eating 4 hours before bed) improves sleep quality, which in turn boosts your prefrontal cortex, enhancing willpower and alleviating mental health issues.

The goal isn't to constantly chase a higher HRV score. A healthy, adaptive nervous system is reflected in a stable HRV that doesn't fluctuate wildly day-to-day. High variability between days can signal overtraining or poor recovery, even if the absolute numbers seem high.

Heart Rate Variability isn't a single number. It's a compilation of 12 to 15 different metrics analyzing heart rate data in various ways (e.g., time domain, frequency domain). The single score on your consumer device is a useful but incomplete picture of your nervous system's state.

To combat stress and improve sleep, data scientist Penelope Lafoy takes short, five-minute walks between meetings without her phone. This practice trains the body to "down-regulate" and shift out of a high-alert state, which makes it easier to fall asleep and improves overall sleep quality.

The popular belief that blue light from devices is the primary sleep disruptor is a myth. New research shows the main issue is the psychologically activating nature of the content (e.g., social media, email) which mutes sleepiness, especially in anxious or impulsive individuals.

Studies show that regularity—going to bed and waking up at the same time—outweighs sleep quantity in predicting all-cause mortality. People with the most regular sleep schedules have a 49% lower risk of premature death compared to those with irregular schedules.

Consuming sugary foods before bed leads to high blood glucose, which activates the sympathetic nervous system (fight or flight). This physiological stress state increases heart rate and body temperature, directly opposing the calm, parasympathetic state required for restorative sleep and leading to poor sleep quality.