Fitness trackers aren’t that complicated: they count your steps, measure your pulse rate and record how long you’ve spent exercising. If they’re sports watches or smartwatches with GPS aboard they can also track your location.

Usually the devices come with the possibility - or the requirement - to connect them to a smartphone or a computer. The collected data is then transferred, saved, and evaluated.

The data analysis often takes place within a dedicated app, but in some cases it can be viewed on the fitness tracker manufacturer’s website after it’s uploaded from the device.

"In my opinion, a fitness band should have these basic functions: pedometer, stopwatch and heart rate monitor," says mathematician Thomas Camminady, a researcher into machine learning at the Karlsruhe Institute of Technology in Germany. He himself uses a GPS watch for running.

The step counters of simple fitness trackers that don’t have GPS work via a motion or acceleration sensor. You can buy one for between US$100 and US$150 .

Very cheap trackers with pedometers and heart rate measurement are also available for around US$30 and can be used even without a user account or a paired smartphone.

A GPS watch has the advantage that it can help you find your way. "For someone like me who runs regularly, the navigation feature is very important, which is why I chose a GPS watch," Camminady says.

"If I upload a route before the run, the watch buzzes at the intersection when I have to turn."

Fitness trackers or watches with GPS start at around US$150 and go up to around US$900 .

Before you buy a tracker, you need to think about what you want to achieve with the device and which functions you need it to have. Otherwise it can quickly end up gathering dust in some corner.

"You should ask yourself why you want to do sports - also from a longer-term perspective - and what supporting role a smartwatch or fitness tracker could play," says Professor Lars Donath, a sports scientist with the German Sport University in Cologne.

For example, what are your specific training goals? How can you reward yourself when you achieve something? Which features of a fitness tracker can support you in everyday sport? The answers to those questions will help you decide what kind of tracker you need.

"A fitness tracker is usually completely sufficient for lower training intensities," says Donath. “With an ordinary fitness tracker, you always know how much and how intensively you have moved. In combination with apps, that's often enough."

Sports watches and smartwatches can generally do a lot more than fitness wristbands. They can manage training plans, recognize different exercises, and even vibrate to remind you of the next training session.

The data is usually synchronized with the manufacturer's server. Although hardly anyone does so, it's essential to read the terms and conditions that apply to a device or app to see how transparent (or not) the data flows are.

Sometimes uploading your data can be beneficial, and you might find it useful to share running or cycling routes with friends or training partners or to document your fitness progress for others to see.

"You can bring your training via the software into a kind of social framework. If you want, you can compare yourself or, for example, collect ideas for new running routes," Thomas Camminady says.

 - dpa