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.
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Last Updated on 8 July 2026 by the5krunner
My favourite kit and nutrition
- Injinji – Runners protect your toes. Avoid discomfort and minor injury. Run more. Run faster. I use them.
- Garmin 90-degree charging adapter — The small adapter that keeps your charging cables tidy. Essential for race day. I use one.
- Garmin charging puck — the fastest and most reliable way to top up your Garmin before a session. I use one.
- Ravemen FR300 — Front light that mounts directly under your Garmin or Wahoo head unit. Keeps your bars clean and your beam pointed where it matters. I use one.
- Body Glide – The blue anti-chafe stick that all swimmers and many runners use. I use it.
- Maurten — The race nutrition trusted by elite athletes. Gels and drink mixes engineered to be easy on the stomach. I use them.
- Garmin Varia RTL515 — A radar rear light that alerts you to vehicles approaching from behind. Pairs with your Edge or Garmin watch. I use this model.
- Favero Assioma Pro RS2 — The power-meter pedals most serious cyclists choose. Accurate, easy to move between bikes. I use this model.
- Garmin Forerunner 970 — A serious choice for a pro-grade triathlon watch. I use this.
- Polar H10 — My daily driver for accurate, waking HRV readings.
- Wahoo ELEMNT Roam 3 — The bike computer that has the feature Garmin lacks: usability. I use mine on most rides.
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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
