What Google told me
I’ve just had some interesting feedback from Google that two of my Fitbit Air accuracy findings helped identify and fix two unusual bugs in the Air’s TCX file export. Here are the details.
The two bugs
Both bugs were in how the Air saved its TCX file, the file that several testers like me use to check the data.
- The first one affected my sampling rate test post. The file made the Air look like it was recording heart rate far less often than it really was. Google says the Air records more often than the file showed, so the slow sampling I measured was the file’s fault, not the sensor’s (Google asserts one point is recorded every 2 seconds). They have offered me API access to check the real data, which I might take up at some point.
- The second one affected a session where the heart rate chart was highly erratic. Google says the file pulled in heart rate data from other devices connected to Google Health for the same workout, which is what made the readings appear to jump between the sources.
What I make of it
Google fixed both bugs and got in touch to explain, which is fair of them. I haven’t re-tested either session myself, so I am taking their word on both. The affected posts now carry a note pointing here.
There is one thing I don’t fully agree with. Google reckons the second session would still show a bit of cadence lock, and puts that down to the band being too loose. My band was as snug as it is in every other test I have run. Cadence lock on a wrist sensor is a known problem, and it is not linked to how tight the band is when I experience it.
Everything else I have written about the Air still stands.
For the full Fitbit Air record and every test: Google Fitbit and Wear OS hub.
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This site covers endurance sport technology across a range of dedicated reference sections. Each one collects the most relevant articles, tests, and analysis on its topic in one place.
Buyer guides
- Best sports watch: tested recommendations by sport and athlete type (triathlon, running, marathon, cycling, hiking, and women)
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- Best wearables: recovery trackers, heart rate monitors, running power meters, and female athlete tech
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Brand and product guides
- Amazfit: the full Amazfit range from Balance to Cheetah to T-Rex, accuracy tests, HYROX partnership, and Zepp Health analysis
- Apple Watch: athlete-first coverage of Apple Watch across running, cycling, and triathlon
- COROS: watches, features, and firmware across the full COROS range
- Garmin: the company, the platform and the full range, and the starting point for choosing across every Garmin product line
- Garmin Edge: bike computers from entry-level navigation to flagship endurance and mountain biking
- Garmin Fenix: every model, feature, and firmware development for Garmin's flagship outdoor watch
- Garmin Fenix 8 Series: which variant to buy, upgrade advice, accuracy data, and the full Fenix 8 review and firmware coverage
- Garmin Forerunner: the full Forerunner line covered from entry level to triathlon flagship
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- Ride with GPS: route planning, navigation and how it works alongside Strava
- Wahoo: KICKR trainers, ELEMNT bike computers, and the Wahoo ecosystem
- WHOOP: strain, recovery, sleep and the full WHOOP ecosystem
Specifications database
- Full Specifications Database: detailed spec sheets, battery life, sensor lists and generation-on-generation comparisons for current Garmin, COROS, Amazfit, Samsung, Google Fitbit, Huawei, Polar, Suunto, Wahoo and Apple Watch models
Glossary
- Sports Technology Glossary: non-branded terminology across running, cycling, swimming, triathlon, hiking, strength training, HYROX, sensors, ecosystems, and brands
Sport and topic guides
- Running Watches: how to choose by discipline (road racing, trail, track, beginner, and multisport)
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- parkrun: technology, training, and performance for the weekly 5K
- Hiking Technology: navigation, safety, and trail tech for walkers and hikers
- Heart Rate Monitoring: optical sensors, chest straps, accuracy comparisons, and how to set training zones
- Optical Sensors (PPG): the 40 things a wrist optical sensor could measure, from heart rate to glucose, ranked by evidence
- GPS Accuracy: how satellite systems perform across brands, terrains, and conditions
- Sports Watch Battery Life: battery claims, real-world tests, and how to manage battery life across Garmin, Apple, Amazfit and COROS
- Recovery Trackers: WHOOP, Oura, and the science of readiness scoring
- Muscle Oxygen Sensors: SmO2 and NIRS explained, Train Red and Moxy compared, and the category from BSX and Humon to Garmin and WHOOP
- Female Athlete Tech: wearables, physiology, and performance for female endurance athletes, covering cycle-synced training, RED-S, HR accuracy, and VO2max
- Sports Science: peer-reviewed research on HRV, VO2max, lactate threshold, running power, wearable accuracy, and supplementation
- Testing Methodology: how this site tests GPS accuracy, heart rate, battery life, and other performance claims
Content series
- Release Radar: confirmed launches, leaks, and rumours across Garmin, Apple, COROS, Polar, Suunto, and Wahoo
- Deep Dive Feature Files: weekly firmware feature updates across all brands (bug fixes excluded)
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Last Updated on 8 July 2026 by tfk the5krunner
Small things I always use
- Garmin 90-degree charging adapter: Charges your Garmin from any USB-C cable. Essential when travelling. I use one.
- Body Glide: The blue anti-chafe stick swimmers and runners carry. I use it.
- Speedo earplugs: Fewer ear infections and no cold-water dizziness. I use them.
- Dryrobe Advance: My winter changing robe for open-water swims. I use one. A cheaper option is the AONYIYI changing robe.
- Maurten: Race fuel that stays easy on the stomach. I use them.
- Garmin charging puck: The quickest way to top up before a session. I use one.
- Injinji: Toe socks that stop rubbing, so you run more. I use them.
- Ultimate toe protectors: Stop black toenails on long runs. They work. I use them.
- Compressport R2 v2 calf sleeves: My calf sleeves of choice. I use them.
- Cellucor C4: My pre-workout before hard sessions.
- TPU tubes: Schwalbe Aerothan, Tubolito and Pirelli SmarTube. Light, tiny spares. I use all three.
- G8 insoles: Adjustable insoles that are good. I use them.
- Cycplus Cube: A 97g electric pump that gets a road tyre rideable in two minutes. I carry one. 5% off with code THE5KRUNNER.
Watches and sensors
- Polar H10: My daily driver for waking HRV.
- Polar Verity Sense: My backup arm-worn HR sensor.
- Nomad bedside charger: Charges my iPhone and Apple Watch overnight. I use it, and many of their bands.
- Train.Red: The best muscle oxygen sensor I’ve used.
- Tymewear: Accurate heart rate and reliable ventilatory zones. I use it to pace endurance rides over an hour.
- Garmin Forerunner 970: A pro-grade triathlon watch. I use this.
- Apple Watch Ultra 4: My daily smartwatch. No phone needed on rides.
- Garmin Fenix 9 Pro: I’ve just bought one.
On the bike
- Continental GP5000 for everyday riding, and Aero 111 on the front for special occasions.
- Helmets: Specialized S-Works Evade 3 for road riding, and Rudy Project Wing for TT-style races. I use both.
- Ravemen FR300: A front light that mounts under your Garmin or Wahoo. I use one.
- Wahoo TRACKR Radar: I use it on one bike and Varia on the other. They perform the same.
- Garmin Varia RTL515: Radar that warns you of cars from behind. I use this model.
- Wahoo ELEMNT Roam 3: The bike computer that’s easy to use. I use mine on most rides.
- Favero Assioma Pro RS2: Accurate power pedals that swap easily between bikes. I use this model.
Home and indoor training
- NPE Runn: Makes my basic treadmill smart, sending more accurate speed and distance to my watch and Zwift. I use it.
- Google Wifi: Keeps Zwift connected in my pain cave. I use it.
- Apple TV 4K: Zwift on the big screen. I use two.
- Google Nest Doorbell (wired, 2nd gen): My video doorbell, running in both Google Home and Apple Home. I use it.
Health, recovery and sleep
- FreeStyle Libre 3 Plus: Shows how my blood sugar responds to diet.
- hDrop: Measures my sweat loss in summer and indoors.
- Fourth Frontier Zone: Checks my heart under load in hard sessions.
- Oura Ring 5: My partner’s recovery tracker of choice.
- Kineon MOVE+: Red light therapy for niggles. It works.
- Eight Sleep: A cooling mattress cover my partner and I use nightly.
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Written by real people, with AI assistance. Fact-checked and verified for originality. See the Editorial Policy. FTC: Affiliate Disclosure — some links pay commission. As an Amazon Associate, I earn from qualifying purchases.
tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. ID
