A common question I receive from many of my athletes regards treadmill running – a question that I’ve had myself and you have possibly had as well. Most runners use a Garmin or other GPS watch to track their runs – it’s a commonplace piece of gear for a majority of runners. The Run Indoor setting on many Garmins allows you to track and record your treadmill run, just as you would an outdoor run. However, several of the runners I coach ask me about the accuracy of the Garmin Run Indoor mode. More often than not, the Garmin record a different distance – and therefore different average pace – than the treadmill.
So which is more accurate – the Garmin or the treadmill? Why is there a discrepancy in the distance between the two? Why is the discrepancy even more prominent on interval workouts than easy runs?
Garmin Indoor Mode Accuracy on the Treadmill
Unless you utilize a footpod, a Garmin tracks distance indoors using an accelerometer (depending on the model, but this is how most function). Accelerometers calculate distance covered based upon your stride length, stride frequency, and arm swing. The accelerometer calibrates based off of your form on outdoor runs. As an accelerometer, the Garmin Indoor mode works very well; the data inaccuracies occur due to individual variations in form from outdoors to the treadmill.
Running on the treadmill is different than running outdoors – especially when it comes to form. As a 2017 study published in the International Journal of Exercise Science notes, stride length and stride frequency tend to different when running on the treadmill than outdoors.
The difference in form on the treadmill versus outdoors makes sense. You aren’t propelling yourself forward on the treadmill, but rather you keeping up with the pace of the belt, which alters your form. The confined space of the treadmill can also cause many runners to change their form. This is especially true if you are worried about flying off the back of the treadmill during intervals or tempo runs and subconsciously shorten your stride.
If the Garmin Indoor mode is calculating the distance run based off of your stride and arm swing, and you change your stride and arm swing on the treadmill, it therefore makes sense that the distance calculated is different than the treadmill reads. The treadmill calculates distance based on the number of revolutions of the belt – unless the treadmill is very old or poorly calibrated, it should be relatively accurate.
Alternatively, you may not change your form too much – so you may not notice any difference!
Most of us runners are analytical numbers geeks – we want the accurate data on our Strava or Garmin Connect and we want to be able to easily track our workouts. These few tips will help you minimize discrepancy between your watch and the treadmill – and help you get the most out of your indoor run.
Focus on Your Form
If the indoor mode of your GPS device and your treadmill read statistically significant differences (say, more than 10% of the distance of the run), your form may drastically different on the treadmill than outdoors.
Whether or not you care about the GPS data, pay appropriate attention to your form on the treadmill. Avoid holding onto the front bars or running at the very front of the belt. Running at the front of the belt can shorten your stride and inhibit your arm swing. Run on the middle of the belt, giving yourself room for your stride and arm swing to open up more naturally. Run tall, avoiding hunched shoulders. Don’t obsessively check your watch, as bringing your wrist forward and craning your head down throws off your form.
Run for Time Instead of Distance
If even a minor distance discrepancy is going to mess with your mind, change your metric and rely upon duration instead of distance. For example, if your normal easy run pace is approximately a 9 minute mile and you want to run 5 miles, run for 45 minutes on the treadmill. If your watch reads short or long, it really doesn’t matter – you will have achieved your prescribed workout.
For speedwork, use time-based interval workouts such as fartleks rather than distance based intervals. The form differences on the treadmill are exaggerated at faster paces, so your watch will likely be more inaccurate during interval runs. If you are using the interval function on your watch, time-based intervals will align with the time readouts on the treadmill. Try a fartlek workout or one of these treadmill workouts for runners.
Remember the Purpose of Your Workout
I think the age of GPS watches and social training logs, we can become slightly obsessive over the preciseness of data and numbers. Ultimately, what matters is the workout itself, which is often defined by volume and intensity. Distance and pace are one method of measuring volume and intensity, but so are duration and perceived effort.
For example, 5 mile and 5.2 miles at an easy effort renders the same workout. Choose which way you want to measure that run on the treadmill and then disregard any minor discrepancy. Don’t obsess too much if your watch and treadmill are slightly different on distance, especially if it’s an easy run. The discrepancy does not negate the purpose of your workout.
A Final Note on Indoor Mode
Yes, indoor mode works well on the treadmill – but let’s not forget about the other type of indoor running, the indoor track. Run Indoor mode will be more accurate on the indoor track than the treadmill, since indoor track running is more similar to outdoor running. You can also use the precisely measured distance of an indoor track (many are 200ms per loop) to confirm the distance and pace of your run.
For more on treadmill running, check out these blog posts:
How to Survive – and Enjoy – Treadmill Long Runs in Winter
Runners Share their Best Treadmill Tips
Do you use your Garmin on treadmill runs? Have you noticed this issue?
How often do you run on the treadmill?
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