Whether you're a fan of GPS running watches or not, most runners wear one on their wrist.
New running smartwatches and fitness trackers are released to the market every year. These high-tech devices are equipped with a dazzling array of features such as programs for different workouts, heart rate monitors, cadence counters and emergency call out capability.
But all the performance monitoring features in the world don't matter if your watch is miles off the mark.
So how reliable is your running watch?
Behind the scenes
Most runners splurge on a fitness watch because they want to be able to accurately monitor and track their distance, pace and heart rate, and to a lesser extent elevation, calories burnt, splits and steps per minute.
Depending on your budget, your running watch could feature a range of hardware including
GPS or Global Positioning System, barometer, accelerometer, magnetometer, altimeter and gyroscope. These sensors, when combined with sophisticated algorithms that are used to collect the data, make for powerful performance measurement.
But technology has bad days too. Ever crossed the finish line of a race, stopped your watch and done a double-take at the distance it has recorded compared with the official event distance? You're not alone.
Is near enough, good enough?
While most technology in your running watch is state of the art, there are inherent limitations that may cause some readings to be inaccurate under certain circumstances. For example, large buildings or the great outdoors can get in the way of a GPS signal, and if your watch isn't fitted correctly to your wrist, the heart rate sensor might not be precise.
Several academic studies have tested the validity of a range top brand running watches. One Japan study that measured 19 adults wearing 12 trackers showed that fitness trackers underestimated calories burned by as much as 590 per day.
The studies say...
Researchers filmed them running four-minute intervals, starting at eight kilometres per hour. Speeds increased by two kilometres per hour after each interval and participants continued until they could no longer complete a full interval.
The study found that non-elite athletes could rely on the device. "Previous research found that at lower speeds Fitbits tended to underestimate step count," said Dr Joanne Kemp from La Trobe Sports and Exercise Medicine.
"Our study found that Fitbit Flex has good-to-excellent reliability for running speeds between eight and 14kms/h, but are slightly less reliable and higher speeds."
Dr Kemp said researchers also compared each of the three Fitbits worn by participants and found differences of between two and six per cent between devices worn on different arms.
How GPS works
GPS or Global Positioning System is standard in most running watches today, and it determines your location through a process called triangulation.
What's triangulation I hear you say? First, let's start with satellites. Solar-powered satellites circle the earth twice a day and work by sending microwave signals to GPS receivers – like that in your watch – to triangulate your location. At any one time your watch needs to detect a minimum of three satellites to pin-point where you are.
GPS works in all weather conditions, but it struggles in populated areas or dense forest, and doesn't work inside buildings, which is why you need to select a different activity program option on your watch if you're running on a treadmill.
The Apple Watch Series 4 goes one step further than GPS to get your running started. Instead of waiting for the watch to lock on to a satellite, it uses Wi-Fi hotspots to pinpoint your exact location, so you'll never be left standing in the street waving your arm around trying to get a GPS signal.
And as a savvy back-up for times when a GPS signal can't be found, the watch uses the accelerometer, which measures motion, to calculate speed and pace.
Does it matter?
Even if your running watch underestimates your heart rate and wrongly measures your distance by a few per cent, does it affect your achievements?
Just because your running metrics might not be 100 percent accurate doesn't mean the technology is useless or your workout doesn't count.
If you're walking more, running more, sleeping more and feeling in control, then the positives of wearing a running watch or fitness tracker on your health and lifestyle far outweigh the negatives.
The goal of one day completing an ultra-marathon inspires running fanatic Laura Hill to clock up the kilometres each week. With a day job in the corporate world, Laura loves nothing more than lacing up her runners and hitting the pavement to clear her mind and challenge her body.
Follow Laura Hill on Twitter