What HRV actually measures
HRV is the millisecond-to-millisecond variation between heartbeats. High HRV means your parasympathetic ('rest and digest') nervous system has room to respond. Low HRV means you're stuck in a low-grade fight-or-flight state, even when you feel fine.
What low HRV does to your day
You wake up tired no matter how long you slept. Workouts feel heavier. Decisions take longer. Your patience runs short by 3 PM. Caffeine works less. Alcohol hits harder. Recovery from anything, training, illness, a hard week, stretches out.
Why sleep is the lever
Roughly 80% of your daily parasympathetic recovery happens during deep sleep. Lose that window and HRV stays suppressed for days. This is why one bad night shows up on your Whoop for a week.
How Sleeptruly helps
Magnesium glycinate calms the nervous system before bed. Glycine deepens slow-wave sleep, the stage where vagal tone rebuilds. L-Theanine and Passion Flower clear residual cortisol so your body can drop into recovery instead of fighting through it.