Guides to stress, HRV and recovery.
Ten guides, reviewed quarterly against the cited literature. The test gives you a number in two minutes. These guides are the longer version: what the instrument measures, what heart-rate variability can and cannot tell you, and which interventions have evidence behind them.
What heart-rate variability actually measures
Why a healthy heart is not a metronome, what RMSSD is counting, how the vagus nerve produces the variation — and why your absolute number matters far less than your own trend.
Read the guide Instrument · PSS-10The PSS-10, line by line
Where the ten items came from, why four of them are reverse scored, what the 0–13 / 14–26 / 27–40 bands actually represent, and the questions the scale was never designed to answer.
Read the guide Mechanism · AgingCortisol, inflammation and allostatic load
How a response built for minutes causes damage when it runs for years: the flattened cortisol slope, low-grade inflammation, and the cumulative cost McEwen called allostatic load.
Read the guide Practice · BreathworkResonance breathing: the six-breaths-a-minute protocol
The one voluntary act with a large, immediate and repeatable effect on heart-rate variability — where the number six comes from, how to find your own rate, and how to practise it properly.
Read the guide Factor · SleepSleep, HRV and the overnight recovery window
Why autonomic recovery mostly happens while you are asleep, what alcohol and late training do to overnight HRV, and why sleep regularity beats sleep duration for nervous-system recovery.
Read the guide Practice · TrainingWhat actually raises HRV — and what does not
A ranked, evidence-weighted list: aerobic base training, alcohol, sleep regularity, breathwork, heat and cold, and the supplements and gadgets that show nothing once you control for measurement noise.
Read the guide Reference · NormsHRV normal ranges by age
A reference table of typical resting RMSSD by decade, why wearable overnight values run 20–50% higher than lab readings, and how to place your own number without being misled by it.
Read the guide Reference · DevicesHow each wearable computes HRV
Oura, Whoop, Garmin, Apple Watch, Fitbit and Polar each count something slightly different. Which metric, which part of the night, and why cross-device comparison is meaningless.
Read the guide Practice · MeasurementMeasuring HRV without a wearable
A phone camera or a cheap chest strap is enough. The morning protocol that makes readings comparable, and the six mistakes that ruin them.
Read the guide Instrument · NormsPSS-10 norms: what the average person scores
US national means from 1983 to 2009, who scores higher, why the 14 and 27 cut-points are conventions rather than clinical thresholds, and how to read your own score against the population.
Read the guideAlso from us: Helixspan
Chronic stress is one of seven modifiable factors that shape how many healthy years you have ahead. Helixspan estimates your projected healthspan from all seven.