Does the Treadmill or Your Watch More Accurately Measure the Distance You’ve Run?
Outdoors, smartwatches are great at telling you how far you’ve run or walked. Indoors, they often disagree with the readings on the gym treadmill. This leaves many of us wondering: Should we trust a treadmill or a watch?
The answer to this question is a treadmill. A treadmill will always give you a better idea of what your legs are doing than a watch. But I don’t blame you for doubting everything you see on the machine’s readings. After all, their calorie counts are notoriously inaccurate .
Why is a treadmill more accurate than your watch (by distance)
Whenever we evaluate accuracy, it is important to know whether the device is measuring something directly or interpreting the data to make an assumption. In this case, the treadmill measures the distance and the watch guesses it. (Calories are always interpreted, so they are never truly reliable .)
Distance is quite simple: it is the number of miles (or meters) of the treadmill that passes under your feet while you run. The treadmill knows its belt length and motor speed, so it directly measures how much belt passes under your feet. (Sticklers will note that technically there is still some interpretation here, since the relationship between the motor’s performance and how much the belt moves can change over time, so calibrating the treadmill is an important thing. But it’s still pretty close, and your best bet is for the purposes we discuss here.)
Your watch, on the other hand, is on your wrist. He can’t know what your legs are doing. It can make some guesses based on how much your wrist swings back and forth, and thus picks up the rhythm (each hand movement corresponds to one step). When you run faster, you will swing your arms a little harder and higher, so he can use the force of your arm swing to guess the speed of your running. From here he estimates the distance.
How to get the most accurate numbers
None of them will be perfect, but the treadmill is much more likely to get the right idea. The treadmill may be slightly miscalibrated and give you a slightly different distance than what you actually ran. But the watch just rides around on your wrist, guessing. I noticed that my arms don’t move any differently when I run at a fast or slow pace.
In fact, while following a treadmill interval workout on the Garmin Forerunner 265 , I found that the watch thought I was going slower than during the fast parts. When he honks to rebuke me (“Pace is slow”), I can reassure him that I’m within reach by pumping my arms a little harder. However, this is not really a solution.
Instead of trying to get more accurate numbers on my watch while running, I approach my treadmill workouts knowing that the following things are accurate:
-
Treadmill speed during workout
-
Treadmill distance at end of workout
-
Heart rate on my watch (especially if I’m using the chest strap )
-
Time from one or both devices (which should be the same if I were running them at the same time)
I then monitor my workouts accordingly. If it’s a heart rate based workout, I let my watch handle everything. (Garmin might tell me to do 32 minutes at 139 to 167 bpm. Great. That’s it, Garmin.)
But if I want to do a workout based on speed or distance, I control it manually, using the human brain. A quarter mile at 7.5 mph repeated eight times? Accordingly, I press the buttons on the treadmill. At the end of the workout, I will either “calibrate” (using the watch) or edit the distance in my app to make sure it recorded the correct total distance.