What HRV actually is
HRV stands for Heart Rate Variability — the tiny variation in time between heartbeats. Not the beats per minute. The milliseconds between beats.
When you're relaxed, those intervals vary a lot. When you're stressed, sick, or under-recovered, they become more regular. Counterintuitively: more variation = healthier, less variation = dysregulated.
Athletes have been using HRV for decades to decide when to train hard and when to back off. Long COVID patients are now using it to understand their autonomic nervous system.
Why it matters for Long COVID
Long COVID messes with the autonomic nervous system (the one that controls heart rate, breathing, digestion). HRV is the cleanest single number we have for tracking that system.
Healthy HRV:
- Your "rest and digest" (parasympathetic) system is doing its job
- You recover well from stress
- Your body is ready to handle more activity
Low HRV:
- You're in "fight or flight" mode
- Your body is allocating resources to survival, not recovery
- Today might not be the day to push
In Long COVID patients, HRV is often significantly lower than age-matched controls and drops further during crashes. Studies show HRV can decrease days before the patient feels a crash coming — making it potentially useful as an early warning signal.
How to measure it
Best: a wearable you wear overnight.
- Oura Ring — measures HRV during deep sleep, shows a daily number. Widely used in LC community.
- Garmin — shows "HRV Status" (Balanced / Low / Poor / Unbalanced) + overnight average in ms
- Whoop — subscription based, gives detailed HRV + "recovery score"
- Apple Watch — takes HRV spot-measurements, not continuous
- Fitbit — includes HRV in some newer models but less reliable than the above
The key: measure at the same time every day, ideally during sleep. HRV varies a lot within a day (it drops during stress and exercise). You want your baseline, not a snapshot.
What the numbers mean
Absolute HRV numbers are very individual. Here's rough context:
| HRV range | What it means | |---|---| | 100+ ms | Young, athletic, well-recovered | | 50-100 ms | Average healthy adult | | 20-50 ms | Typical Long COVID range | | < 20 ms | Significantly dysregulated |
Don't compare your HRV to someone else's. Track your own trend. A week of 25 ms is normal for you if your usual is 25. A drop to 15 ms is meaningful.
How to use HRV without becoming obsessive
This is the hardest part. Research shows that obsessive health tracking can increase anxiety, which in turn lowers HRV, which makes you more anxious — a vicious loop.
Healthy use:
- Check it once a day, in the morning
- Track trends over weeks, not days
- Use it as one data point among several (how you feel, your symptoms, your sleep)
- Let it inform decisions about activity level, not emotional state
Unhealthy use:
- Checking every hour
- Canceling plans because of a single low reading
- Feeling personally responsible when HRV drops (it's not your fault)
- Catastrophizing normal fluctuations
Practical tips
- Context matters. A low HRV after 3 days of poor sleep is not the same as a low HRV after 3 days of great sleep.
- Morning context is cleanest. Measure at the same time, ideally while still in bed.
- Breath work raises HRV. 5-minute paced breathing (6 breaths/minute) before sleep improves overnight HRV for most people.
- Hydration affects HRV. Dehydration lowers it.
- Alcohol tanks HRV for 24-48 hours, sometimes longer in LC patients.
The goal is not a number. The goal is to know yourself better so you can make smarter choices about energy.