Insights, category: Measuring

Deep sleep, also known as slow-wave sleep or NREM Stage 3, is the heavy-duty restoration phase of your sleep cycle. It’s when your body goes into full-on repair mode—muscles rebuild, tissues grow, your immune system gets stronger, and your brain cleans out waste.

Heart rate variability (HRV) measures the variance between each heartbeat controlled by the autonomous nervous system (ANS). This system operates behind the scenes, regulating vital body functions such as heart rate, blood pressure, breathing, and digestion. The ANS is comprised of two systems: the sympathetic nervous system, responsible for fight or flight responses, and the parasympathetic nervous system, responsible for relaxation and recovery.