The r/longevity thread about consistent HRV improvement since 2018 is worth sitting with, but there’s a confound almost nobody in that discussion names: wearable HRV algorithms have changed significantly over that same window. Apple Watch, Garmin, and Whoop have all updated their calculation methods multiple times since 2018. What’s being reported as RMSSD in 2026 is not necessarily the same calculation as 2018 on the same device family, let alone across device switches. The second thing I’d flag is metric heterogeneity. HRV isn’t one number. SDNN, RMSSD, and HF power capture different aspects of autonomic regulation and don’t always move together. Most wearables report RMSSD now but didn’t consistently before 2020 or so. If someone switched devices mid-period, the baseline comparison is essentially meaningless. That said, direction still matters even if magnitude is uncertain. A consistent upward trend across 8 years, same device and morning-resting conditions, is harder to dismiss than a single reading. I’ve been logging morning HRV alongside sleep and subjective wellbeing markers for about two years now. The trend line view in CareClinic is what kept me honest about it, actually, bc it’s easy to remember the good weeks and conveniently forget the six weeks after a stressful period when the trend went the other direction. The long arc tells a different story than the daily number. What I’d want to know about that thread: what’s the actual intervention? Exercise, sleep, something compounded? Without naming what changed, eight years of improvement is an interesting observation, not a lesson.