Feelmo Journal
Apple Watch HRV, heart rate and sleep, explained for anyone starting out — written to help you follow your own trend rather than judge a single value.
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You caught up on sleep at the weekend, yet Monday still feels difficult. Research helps distinguish extra sleep from a shift in sleep timing, with practical ways to ease back into the week while protecting the rest you need.
7 min read
Could afternoon coffee affect your sleep? A gentle, research-based explanation of caffeine dose, timing and individual differences, with manageable changes and ways to review sleep using Apple Watch or Feelmo.
7 min read
What the HRV figure on your Apple Watch actually represents, how it differs from heart rate, what SDNN means, and what to watch for when reading the number.
4 min read
How to read a low HRV reading on Apple Watch. Rather than judging by a single value, work through measurement conditions, your own baseline, sleep and exercise, and your symptoms.
5 min read
How to record sleep with Apple Watch and read sleep duration, sleep stages, heart rate and HRV on iPhone — from the initial setup to what to look at in the morning.
5 min read
Why a long night can still leave you tired: how rested you feel, waking in the night, your body clock, daily habits, and the possibility of a sleep disorder.
6 min read
How HRV relates to fatigue, stress and recovery, and how to read it alongside your own baseline, your sleep, your heart rate and your symptoms.
5 min read
Separate from Apple's native sleep feature, we tested a research model using heart-rate-derived information and temporal context from public Apple Watch data. The specific feature design, preprocessing and model architecture are unpublished. This unreviewed internal secondary analysis explains both the results and their limits.
8 min read
Using HRV-derived information, we linked two sections from the same session among 202 people. The signal exceeded a random baseline, but it does not establish identity verification or performance across days. Aggregate results are public; implementation details are unpublished.
7 min read
Sex differences in HRV depend on the metric, age, breathing, recording length and device. Large studies and an exploratory re-analysis of 1,173 people across four public datasets show why group averages must be separated from individual judgment.
10 min read