Apple Watch sleep stages missing? What to check
Apple Watch sleep stages missing? Learn why sleep can show as Asleep without REM, Core or Deep, and check the source, tracking setup and app permissions.
Low HRV but feel fine? What to check before you train
Low HRV but feel fine? Check your baseline, measurement timing, sleep and recent training before interpreting a low Apple Watch reading or recovery score.
Why HRV apps show different numbers on Apple Watch
Different HRV readings in Bevel, Athlytic, StressWatch or Welltory? Compare formulas, timing and recovery scores from the same Apple Watch with this guide.
10 Best Apple Watch HRV & Stress Apps in 2027
Compare ten apps for HRV, stress and recovery, with practical reasons to choose each, purchase models and links to their current features.
What is Strain? Understanding your daily load
Learn how daily and workout Strain differ, why the 0–21 scale is nonlinear, and how to read your personal range, TRIMP and training load. Includes 14 app screenshots.
How Often Does Apple Watch Measure HRV?
Series 12 and Ultra 4 can measure HRV as often as every five minutes. See how earlier watches differ, what happens during sleep, and how to check your actual recording times.
Baevsky Stress Index Explained: Formula and Interpretation
Understand the BSI formula with a worked example, learn what high and low values mean, and compare the original index with stress percentages and the Kubios scale.
MxDMn Explained: What Your HRV Range Means
See how the longest and shortest heartbeat intervals determine MxDMn, why extreme values matter, and how to read the result alongside AMo50 and Stress Index.
AMo50 Explained: What High and Low Values Mean
Understand the percentage in your HRV report, see a worked example, and learn how AMo50 differs from pNN50 and contributes to Baevsky Stress Index.
Can Apple Watch Measure Cortisol?
What HRV and stress scores can tell you, how cortisol is tested, and how to follow your readings with Wellhero.
