Half‑marathon heart‑rate comparison: WHOOP 5.0 MG, Polar Loop, Amazfit Helio Strap, Garmin Enduro 3 vs Polar H10
Date
Nov 17, 2025
Category
Performance
As promised in the previous comparison - Three months with WHOOP MG 5.0, Oura 4, Polar365/Loop, Garmin Instinct 3, Helio strap - here’s the follow‑up focused on half‑marathon heart‑rate measurement.
I also incorporated feedback from the last post; this time I included the Polar H10 as a reference device.
Hi folks,
I raced a half‑marathon wearing four popular no-screen devices (+ Garmin Enduro 3 as my pacer) to compare heart‑rate measurement during a race. The line‑up: Polar H10 as the gold‑standard reference, WHOOP 5.0 MG, Polar Loop, Amazfit Helio Strap, and Garmin Enduro 3.
TL;DR
Helio Strap showed near‑perfect agreement despite wrist placement.
WHOOP 5.0 MG tracked closely overall, with a few brief motion‑related spikes.
Garmin Enduro 3 followed the trend but was noticeably noisier.
Polar Loop underperformed in this run with bias at higher intensities and more variability.
Overview of the race data
Below is the multi‑device HR trace and the cross‑device correlation matrix for the full race.
It's impossible to see stuff here, so I pasted pairwise graphs below to make the differences easier to see.
Spearman correlation:
Pearson correlation:
Context and setup
WHOOP 5.0 MG on the bicep with the original sleeve
Helio and Polar Loop on the right wrist, with Polar Loop closer to the wrist bone
Garmin Enduro 3 on the left wrist
Polar Loop and Enduro had the least favorable positions
H10 on chest served as the reference for pairwise comparisons
I used Spearman correlation for trend alignment
I trimmed each device’s start time to the same timestamp
Cool day, 8°C / 46°F. A proper warm‑up avoided early reading issues
Correlation vs Polar H10 (reference)
Pairwise notes (see charts below):
Helio: lines almost superimposed after the opening ramp. Small, consistent offset on a few peaks, otherwise excellent agreement.
WHOOP: strong overall; occasional narrow spikes that resolve quickly without sustained drift.
Enduro: follows the trend but introduces noisy excursions, improves towards the end - I don’t remember if I tightened the strap mid race.
Polar Loop: widest deviations. Peak bias and delayed response. A bit better in longer steady patches.
Placement matters. WHOOP had the bicep advantage. Helio did this on the wrist, which makes its result more notable. Enduro and Loop had less favorable positions; Enduro’s mass likely increased micro‑motion. Tightening the strap further may help next time.
Ranking
Helio Strap → clear winner
WHOOP 5.0 MG → close second, weird spikes
Garmin Enduro 3 → generally aligned yet spikier
Polar Loop → clear bias at higher intensities and more variability
H10 pair sections
H10 vs Helio Strap
H10 vs WHOOP 5.0 MG
H10 vs Garmin Enduro 3
H10 vs Polar Loop
Comparison with earlier tests
This half‑marathon continues a familiar pattern: wrist sensors can align well in steady‑state work, while placement and fit dominate the outcome. What’s new is the ranking shift:
Polar Loop topped my earlier triathlon test, yet underperformed here,
Helio delivered near‑perfect agreement despite wrist placement - did well as in previous tests
Whoop overall better this time, still has issues even on bicep.
What’s next
I’ll probably do some other tests, let me know if there is a comparison you’d love to see.
Why I did it
This is part of my r/reThrive (check it out, it's cool I promise) side project that turns wearable data into your body age. If multiple devices tell similar stories, that builds trust. If they disagree, I want to know where and why.
