u/the5krunner

On the Forerunner 970 the optical heart rate sensor sometimes stops tracking correctly overnight. The watch records the first part of sleep normally, then resting heart rate jumps from the low 40s to a stuck reading near 119 for the rest of the night, stress sits at 100, and no HRV is recorded. Sleep stages, Body Battery, and recovery figures for that night are lost. Owners on this thread report the same pattern on current firmware across multiple units.

The sensor does not recover on its own once this starts. It keeps returning the invalid value until the watch is restarted, so the gap runs until morning if nothing intervenes. Turning off sleep mode after waking clears it, but the night data is already gone.

• The only reliable intervention is to restart the watch as soon as you notice the stuck reading. If you check the watch in the night and see a heart rate that does not match how you feel, a restart at that point recovers the sensor and allows the remainder of the night to be tracked correctly. Waking to a normal resting heart rate on the display suggests the episode did not occur. Waking to a reading above 100 with stress at maximum confirms it did.

Garmin has not issued a firmware fix for this. Wearing the strap slightly higher on the wrist and ensuring it is snug before sleep reduces how often the fault triggers for some owners.

After updating a Fenix 8, Fenix 8 Pro, or Enduro 3 to stable software 21.25, the watch reboots on its own during activities and during normal use. Reports cluster around scrolling through glances during a run, a track change in a connected music app, and cold conditions. The activity pauses at the crash point and resumes after the restart, so recorded data is usually kept, but the interruption lands mid run, mid ride, and during ski touring. Owners on this thread confirm the behaviour started only after 21.25.

A full factory reset does not stop it for most owners, which points at the firmware itself rather than a corrupted setting. The crash is reproducible enough that some owners trigger it by scrolling the same screens each time, which rules out random hardware faults on individual units.

The fix is software 21.30. After installing it the reboots stop. Install through Garmin Express over USB, or accept it over Bluetooth or WiFi once the rollout reaches your unit, then repeat the activity that crashed before to confirm. Garmin support gave a separate workaround to owners still on 21.25: recalibrate the buttons from the system settings, which reduced frequency but did not clear it.

Did updating to 21.30 stop the random reboots on your Fenix 8?

I tested the Amazfit Balance 3 for swimming HR accuracy at an outdoor 36m pool, with the Garmin FR970 and a chest strap as cross-references. The Balance 3 showed dropouts and a wider limit of agreement than the Garmin HRM 600 and Polar SENSE, which on the face of it puts it third. The more interesting finding is that the HRM 600 likely overestimated HR during the two harder efforts toward the end of the session. Overestimation in a higher zone carries a disproportionate physiological impact on TRIMP, CTL and ATL, which matters if you are using that data to manage training load. The Balance 3 overestimated in Zone 1, which is largely irrelevant. Lap counting was 100% accurate at a custom 36m pool length, with the FR970 as a cross-check.

Is a chest strap that overestimates during hard efforts actually more useful for training load management than a wrist sensor with dropouts at low intensity?

Further reading: https://the5krunner.com/2026/06/26/amazfit-balance-3-swimming-accuracy/

Awesome Maps is a Connect IQ datafield and glance widget that streams premium map tiles to any modern Garmin on demand. Providers include Ordnance Survey (GB), IGN (France/Spain), Swisstopo, LINZ (New Zealand), Kartverket (Norway), NGI (Belgium), USGS (USA), plus satellite and OpenHikingMap.

The headline implication: a Forerunner 70 at £220 effectively gets richer mapping than a Forerunner 970 at £620, because on-device map content has historically been a software price-point definer rather than a hardware one.

Caveats are upfront in the article:

1. it does not (yet) follow uploaded routes, and
2. the first tile load needs a mobile data connection (it then caches).
3. It is freemium, with full unlimited access at £3.49 per three months.

Built by an indie developer with a spatial data background who handles the geodetic transformations needed for accurate OS coordinates himself.

More details

https://the5krunner.com/2026/06/26/awesome-maps-garmin-ordnance-survey/

Any other suggestions for free maps on Garmin?

I ran a controlled calibration test on the hDrop sweat sensor today: HYROX half sim, nude weigh-in before and after, nothing consumed during the session. Body-mass delta came out at 1.50 kg (1.50 L). hDrop measured 2.055 L, a 37% overestimate. The same direction showed up across two earlier sessions (Stockholm HYROX sim and the Dartmoor Classic), though neither had a rigorous weigh-in to confirm the figure.

The likely mechanism is indoor pooling. hDrop uses conductivity electrodes that need liquid sweat to produce a reading. Outdoors, sweat evaporates and skin stays relatively dry between cycles. In a low-airflow gym, sweat accumulates and keeps the electrodes saturated, so the algorithm reads a higher local rate than the body-weight change supports. Today's sweat rate was around 0.9 L/h, below hDrop's 1.5 L/h adaptive calibration threshold, so the high-sweat-rate algorithm wasn't the cause.

Sodium concentration held up better: Dartmoor plateau was 57 to 65 mmol/L, stable across the final two hours.

Working correction: divide the hDrop fluid loss figure by 1.37.

Is a single-site conductivity sensor ever going to give reliable absolute fluid loss figures, or is it always going to need a personal calibration run?

Further reading: the5krunner.com/2026/06/24/hdrop-calibration-fluid-loss/

The Wahoo BOLT V3 and ROAM V3 are both on sale for Prime Day 2026 -- first time either has been discounted since launch. BOLT at $297, ROAM at $380. The KICKR CORE 2 is also 15% off, which is notable because Wahoo trainer discounts outside of Black Friday are rare. The ACE bike computer is down $80 too if you want the top-end option with the wind sensor.

Full links for US, UK and EU here for further reading: the5krunner.com/2026/06/23/wahoo-prime-day-deals-2026/

Is a first-ever sale on the V3 computers enough to pull buyers away from Garmin Edge at similar price points?

The Polar Loop Band is $30 off for Prime Day 2026 -- first time it's been discounted since launch. At $169 it sits in the same space as the Fitbit Air as a screenless wearable focused on recovery rather than real-time training data. The H10 and H9 chest straps are also down ($89 and $55 respectively), which is useful if you need a reference strap or a budget dual-protocol option.

Full links for US, UK and EU here for further reading: the5krunner.com/2026/06/23/polar-prime-day-deals-2026/

Is the Loop Band actually a credible alternative to the Fitbit Air at this price?

IntervalCoach reads more than 60 recovery and fitness signals every morning (HRV, sleep, sleep debt, training load, subjective wellness) and rebuilds today's workout from that, rather than handing you a static plan and assuming you'll follow it whatever the data says. Multi-sport in one plan, so cycling/running/swimming/strength all sit in the same engine rather than separate calendars.

What caught my attention: the data stays in your own Intervals.icu account rather than getting locked into a closed platform, and the writeback goes straight to Garmin, Wahoo, etc. via the existing integrations.

Free tier with a weekly plan, 14-day trial of the adaptive engine, then €3/month Pro or €8/month Max (the latter adds a Coach+ AI chat).

Full piece with the integrations list and how the engine actually works:

https://the5krunner.com/2026/06/23/intervalcoach-ai-training-app/

Runalyze quietly launched an official MCP server on 9 June. It connects an AI chat tool directly to your Runalyze account, with your permission, and exposes far more than activity history: CTL, ATL, TSB, HRV baseline, marathon shape, plus a full health layer of sleep, resting heart rate, blood glucose, blood pressure and more.

What makes it interesting is the aggregation. Runalyze pulls from Garmin, Polar, Suunto, COROS, Whoop, Oura and others, so the AI sees a consolidated multi-source picture that COROS or Strava connectors, tied to one ecosystem, cannot match. It follows COROS in May and Strava in June, so the pattern is now three platforms deep.

Runalyze's own analyses are calculated outputs, so the MCP hands over the answer, not the method, which protects Runalyze for now. The platforms with less to fall back on are the coaching tools that exist mainly to turn data into recommendations. That is a job an AI can now do across a broader dataset.

Once AI can reason correctly over training data, will the dedicated analysis platforms have any reason to exist?

Further reading: the5krunner.com/2026/06/22/runalyze-mcp-server/

On firmware 31.29, the Edge 1050 displays NaN rather than a time value in the Shimano Di2 time-in-gear data field when the drivetrain is configured as a 1x single chainring setup. The field works correctly on 2x setups and on earlier firmware, so the fault is specific to 1x Di2 configurations introduced or changed in the 31.29 build. Owners on this thread report the field appearing correctly after a ride restarts but returning to NaN partway through or after a sensor reconnection.

• Removing the time-in-gear field from the data screen and re-adding it clears the NaN display temporarily for some owners. The field reverts after the next Di2 reconnection or power cycle, so this is a workaround for a single ride rather than a fix.
• Configuring the Di2 system as 2x in the Shimano E-TUBE app and then setting the front derailleur to a fixed position replicates a 1x behaviour while satisfying the Edge firmware's 2x data model. Several owners have used this to restore correct time-in-gear data. It is an awkward workaround but the only one confirmed to hold across multiple rides.
• Firmware 31.30 appears to be the correct fix but the NaN behaviour is not listed in the release notes but owners who updated report the field displaying correctly on 1x setups after the update.

Did updating to 31.30 resolve the NaN display on your 1x Di2 setup?

On firmware 31.29, typing an address or place name into the navigation search menu and pressing search causes the Edge 850 and Edge 1040 to display Saving Diagnostics and reboot. The device rides and records normally until the navigation search is opened. Owners on this thread report it across both 2025.10 and 2026.xx map versions, which points to the on-device search index rather than a specific map file.

• The workaround while waiting for the update is to deactivate the map in the Maps settings. This removes the search index that triggers the reboot. Routes built in Garmin Connect, Komoot, or Ride with GPS and sent to the device still navigate correctly, because a loaded course does not call the address search function that causes the crash.
• The crash is resolved in stable firmware 31.30. Install it through Garmin Express over USB or accept it over WiFi once the rollout reaches your unit, then test an address search before relying on it for a navigation-heavy ride.

Let us know if deactivating the map or updating to 31.30 resolves the search crash on your Edge?