HRV & Heart-Rate Monitoring

Heart Rate Variability (HRV) measures the variation between heart beats — high variability = parasympathetic / recovered; low variability = sympathetic / stressed or fatigued. The single most useful daily readiness signal for trained athletes, and the cornerstone of how Whoop, Oura, and Garmin Body Battery work.

Sister sections: Apple Watch, Garmin, Oura & Whoop, Running & Cycling, Sleep Tracking, Quantified Self DIY, Breathwork & Vagus, BLE & Bluetooth IoT.

Hardware: chest straps (best accuracy)

• ★ ★ Polar H10 — the industry-standard chest strap; the most-cited gold reference for HRV research; ~$90; BLE + ANT+ + 5 kHz; replaceable battery; pairs with anything.
  • https://www.polar.com/en/sensors/h10-heart-rate-sensor
• ★ Garmin HRM-Pro Plus — chest strap with running dynamics + step counting when not paired; ~$130; dual BLE + ANT+.
• Garmin HRM-Dual — cheaper Garmin strap (~$70); BLE + ANT+; no running dynamics.
• Wahoo TICKR / TICKR FIT — TICKR is chest, FIT is forearm; ~$50-80; reliable BLE.
• Coospo H6 / H9Z — budget chest straps; ~$25-40; surprisingly accurate.

Hardware: forearm / wrist optical (good enough)

• Wahoo TICKR FIT (forearm) — optical; reliable for steady-state cardio; not great for HRV.
• Polar Verity Sense (forearm / goggles) — optical; the best optical HR sensor; sometimes used for HRV in steady-state.
• Apple Watch / Garmin watch / Oura / Whoop — wrist or finger optical; HRV reasonable for trends, not absolute values.

Reality: optical wrist sensors are 80-90% accurate at steady state, often noisy during intervals or strength training. For HRV specifically, chest strap > optical, period.

HRV apps (mobile)

• ★ ★ HRV4Training — paid (~$10 one-time iOS / ~$10/yr Android); camera-finger HRV measurement OR external strap; daily morning measurement → readiness; Marco Altini (researcher) is the author; the most defensible methodology in the consumer space.
  • https://www.hrv4training.com/
• ★ EliteHRV — paid + free; pairs with chest strap; daily morning ortho test (lying-to-standing); great teams + coaches feature.
• Welltory — paid + free; HRV + stress; gamified; good for non-athletes.
• Cardiogram — paid + free; long-term HR + AFib screening for Apple Watch / Wear OS.
• Hrv4Biofeedback — paid; same author as HRV4Training; biofeedback breathing.
• Inner Balance (HeartMath) — paid hardware + app; biofeedback / coherence.

On-watch HRV

• Apple Watch — overnight + workout HRV (SDNN); reasonable trend; not as actionable as a morning measurement.
• Garmin — overnight HRV Status (Forerunner 255+, Fenix 7+, Epix); "balanced / unbalanced / poor" trend bands; the most usable on-watch HRV.
• Oura — overnight HRV; daily Readiness uses it.
• Whoop — overnight HRV; daily Recovery uses it.
• Polar Vantage / Pacer — Nightly Recharge.
• COROS — Nightly Heart Rate / HRV.

DIY / pro-tier

• Kubios HRV — paid + free; the research-grade HRV analysis app; imports .fit / .txt from Polar / Garmin straps; Lyapunov / detrended fluctuation / Poincaré plots — every metric you've heard of.
• pyHRV / hrv-analysis — Python libs for batch HRV; the Quantified Self crowd's choice.
• OpenAnt / ant_fec Python — read ANT+ HR straps directly on a Linux box.

Practical guidance

• ★ Measure first thing in the morning, lying flat, before coffee — daily, 1-3 min reading; only the trend matters. Single-day numbers are noise.
• ★ HRV is highly individual — your "high HRV" might be 30; an elite cyclist's might be 120. Trends matter, not absolute numbers.
• Drops correlate with: alcohol the night before, illness, hard training the day before, jet lag, dehydration, anxiety, late meals.
• Rises correlate with: rest days, cold exposure (sometimes), good sleep, breathing exercises (long term).
• Don't make decisions on a single day's HRV — most apps require 60+ days of baseline to be meaningful.

Resting HR (still useful)

• Resting HR trend is the simplest readiness signal — a 5+ bpm spike from baseline = something's off (cold, hangover, overtraining).
• Apple Watch / Garmin / Oura / Whoop / Fitbit all surface this trend automatically.
• Garmin's Body Battery = HRV + RHR + activity + sleep blended into a 0-100 scalar; the most popular consumer "readiness" surface.

Cost / license honesty

• Polar H10 — ~$90; the gold-standard chest strap, no sub.
• HRV4Training — ~$10 one-time iOS / ~$10/yr Android.
• EliteHRV — free with paid tiers (~$10/mo for full Coach features).
• Whoop's HRV is sub-gated; Oura's is sub-gated; Garmin's is free with the watch.
• Kubios HRV Standard — free for personal use.

Pick this if…

• One pickup answer for HRV-curious: Polar H10 + HRV4Training.
• Already have a Garmin / Apple Watch: start with on-watch HRV trend; add chest strap if you care more.
• Coach-led team / serious athlete: EliteHRV.
• Researcher / DIY analytics: Kubios + Polar H10 raw RR-interval export → Python hrv-analysis.
• Don't want a subscription: Polar H10 + Apple Watch HRV view (free) or Garmin Body Battery.
• Stress / breathing-focused: Inner Balance or HeartMath; see Breathwork & Vagus.