Fitness trackers have been all the rage these days. It seems like almost everybody has one on. They are great at motivating you to get off your ass but…

If you happen to be training for that marathon and are relying on a fitness tracker to measure distance, you may just be missing the mark. Not all fitness trackers are built the same. Even if the same manufacturer makes them.

Test have found that some trackers are incredibly inaccurate. With up to a 32% error for both over or underestimating distance traveled. Accurate distance tracking is essential for marathon training.

The worse performers were found to be trackers without GPS location built-in.

Relying on your step count instead. Usually, this will be based on an estimated stride length multiplied by the number of footfalls, worse still are those trackers don’t allow you to add your measured stride length, which can affect accuracy even more.

GPS watches are usually more accurate than apps and don’t kill your phone’s battery. GPS works by trilateration, meaning your receiver picks up signals from a number of satellites to work out your exact position.

But that doesn’t mean that they aren’t fallible and can be hampered by atmospheric conditions, tall buildings, and tunnels. One study found the error was up to 6%. Which is excellent for a rough guide.

Multiple tests have shown that the best GPS trackers come from Garmin, Apple, and Suunto.


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