Just a couple of week ago Riyad posted his review of the Polar RS800CX. This is a top of the range device that is at home being used by single sports enthusiasts as those engaged in several different activities. Anyone interested in multiple sports will be drawn to the range of bundles and accessories on offer including a cadence sensor for those who like to work out on two wheels, a stride sensor for those who prefer two feet, and GPS and heart rate monitor for both.

Bearing in mind the extreme flexibility of the Polar RS800CX I decided to take a look at it with a fresh pair of eyes, and to concentrate on its use for running. As Riyad has already tested the Polar RS800CX with the G3 GPS I decided to try it with the S3 Stride Sensor.

 I’m not going to reiterate what Riyad has already written in his review, and it would be a good idea to read that in addition to this article to get a more rounded picture of the Polar RS800CX. In particular if you want to know about the ProTrainer software, Riyad’s review covers that and I am not going to cover it again here.

I used exactly the same RS800CX unit as Riyad did, the only addition is that Polar sent me the S3 Stride Sensor. This costs £125.00 if you buy it as an add-on.

If you buy the Polar RS800CX with the S3 Stride Sensor as what Polar calls the RS800CX RUN it’ll cost £464.50.The package includes the training computer, heart rate monitor, S3 Stride Sensor, iRDA USB adaptor for getting data onto your PC, ProTrainer 5 software CD and manual.

Set up and configuration

The RS800CX is an incredibly complex and powerful fitness computer which you can programme to the nth degree. You can combine different exercise sessions on the computer, and upload data to the ProTrainer software for detailed analysis.

However you can use the RS800CX right out of the box with minimal time spent on set up, thanks to some pre-configured exercises that are present as standard. The only information you absolutely must enter as soon as possible is your height, weight and sex. You’ll need to set the time and date too, of course.

The computer has several exercises built into it, called Free, Basic, Interval and OwnZone. You can also create new exercises directly on the computer or on the ProTrainer software from which they can be uploaded.

OwnZone is the most personalised exercise the computer can deliver without access to the ProTrainer software. Each time you do an OwnZone exercise you start with a short regime of slow to fast walking and slow to fast jogging to let the computer work out your heart rate and then the OwnZone exercise is tied in to this. The idea is to give you a tailored workout every time. As you get fitter your heart rate measurements should change, so this is a way to get a fairly personalised workout with the minimum of fuss.

At the other end of the spectrum you can use the Polar RS800CX in the Free zone. In this mode the computer simply records time, distance and heart rate data.

Setting up the S3 Stride Sensor is easy enough. The first stage is the physical setup – you need to put its battery in place and use its very robust lace-hook mechanism to fix it to your shoelaces.

It is quite large unit, and is very noticeable on your shoe.

Because it is a relatively expensive piece of kit, you may want to take the S3 Stride Sensor off your shoe when you are not training. But there is another reason apart from the monetary value for removing the S3 Stride Sensor from your shoe. You can actually calibrate the device for three different pairs of shoes. Riyad mentioned in his review that you can calibrate the RS800CX for three bikes too.

Now at first this might seem like overkill. Cyclists might use more than one bike with different wheel sizes for different types of training and/or terrain but while runners may train on different surfaces and use different shoes, there isn’t a direct link between shoe and stride length. That’s really more related to what you are running for – a 5k race, a half marathon, or a nice steady trail run, and the kind of terrain you are on – fast and flat or rugged and hilly, for example. Your choice of shoe might vary, but it isn’t always the vital factor that affects stride length.

However, there are two runners in my household with different stride lengths, and we could very easily share the use of one S3 Stride Sensor. For those that think this is an expensive piece of kit, there is a strong argument for saying that sharing it with another person effectively halves the cost. As long, of course, as you don’t want to go for training runs together!

As with any stride sensor you really ought to calibrate the S3 Stride Sensor. If you don’t it can only make a best guess as to how much ground you cover with each stride and unless you are very lucky it will be way off beam. There are two ways to do this. One involves running a known distance, making a note of what the Polar RS800CX reports as the distance covered, and using this to work out a ‘calibration factor’ using a simple algorithm. You can enter the calibration factor into the RS800CX at any time.

The other way is ‘on the fly’ calibration. Again you need to run a known distance starting the RS800CX when the run begins and taking a lap measurement when you’ve reached the end of the distance. Then you can go through the menus to set the true lap distance rather than what the computer thinks you ran.

This is the method I chose. I used a separate GPS unit to measure a km of running, and did an on the fly calibration for that before starting a new ‘free’ run and going for a further 9k.

This worked OK, but you can’t walk through the calibration instructions before you are on a run to see the procedure in action as the necessary menu options are only available when the computer is receiving data from the S3 Stride Sensor. The process is quite straightforward, but I found it helpful to carry a note of the steps involved in my pocket.

In use

I have to agree with Riyad that Polar RS800CX is very comfy to wear. It has a slightly curved shape, which makes it snake around the wrist very nicely. The wrist band is flexible, and there are plenty of notches so you can get a comfortably tight fit. I have a very small wrist, and the Polar RS800CX did feel a little chunky, but because the fit is comfortable and the computer is lightweight wearing it was no problem.

While the large front start/stop/lap button is very easy to hit, I found the side buttons a bit on the tricky side to use when wearing the computer. They are a bit small, and the glossy silver finish made them a slippery – particularly so when my hands were wet – with sweat or rain!

The Polar RS800CX is very versatile in terms of the information it can display. You have access to three lines of data at once offering various combinations of heart rate, speed, pace, calories burned, overall time, heart rate zone, lap time, countdown timer, ascent completed, current altitude and more.

There are some preconfigured groupings of three lines, and if you don’t like any of them you can customise what is displayed making selections on the RS800CX itself or using the ProTrainer software. If you create specific exercises in the software and download these to the Polar RS800CX, there is a separate display for data relating to these.

Still, I found the display a bit disappointing because it is tricky to read. The contrast on the LCD display is not great, and the digits on screen are small. When there are multiple elements to look at it can be difficult to see information at a glance when running along.

Take the OwnZone display, for example. The bar in the centre of the screen on the photo below is a representation of heart rate. During a run a miniature heart moves along the bar giving a visual cue as to how far you are within, or towards the limits of, a heart rate zone. It is a great idea, but the information was just too small for me to see easily while on the move.

The good news on this front is that the RS800CX beeps at you if you fall outside its heart rate zones, giving an aural indication that something is wrong. So you could choose to glance at the computer only when it indicates something is amiss.

The menu system is fairly intuitive to work through, but when it comes to setting up exercises on the watch you could get a bit confused. If you want to set up a new exercise completely different from those built into the RS800CX, you can setup a mix of heart rate zones, speed or pace, and distances, configuring very complex interval based sessions if that’s your desire. But it is fiddly. At least you probably aren’t going to want to set up too many complex new exercises and, as I’ve said already, you can also use the ProTrainer software to set up exercises which some people will find easier.

I haven’t mentioned the heart rate monitor at all, and it does deserve a mention. Both the HRM unit itself and the strap are a little on the chunky side, and while I did not find it uncomfortable to wear I was certainly more aware of its presence than the Suunto HRM which is the most comfortable I’ve tried so far. It and the RS800CX had no trouble communicating with each other, though.

As for the Polar RS800CX with S3 Stride Sensor’s ability to accurately record distances, on a test 10k run it was a couple of hundred metres short of my GPS watch’s distance measurement.

Now, 200m out of 10,000m is not enough to make most people grumble. Run any 10k race and even if it is measured accurately you can do more than that amount over or under the distance. But my test shows that one – or possibly even both – measuring system is inaccurate. As a general rule I’d much rather rely on GPS than a stride sensor. In the case of the Polar RS800CX this is no problem as I could opt for the GPS unit that Riyad tested instead of the S3 Stride Sensor.


It really is impossible to cover the range of features in the RS800CX without writing a thesis on the subject. It is so very flexible that athletes involved in all manner of different sports should be able to tweak it to meet their needs, and I am talking about serious, high performance athletes looking for top notch achievements as well as anyone seeking to better their own performance.

I’ve not, for example, covered the way you can use the RS800CX to discover and track your V02max, though this is something many people will find extremely useful.

I can’t really fault the Polar RS800CX for the range of features on offer, then. But it is not the most user friendly of devices. Its relatively poor screen made it difficult for me to get the most from it while on the run, and some people may find the setup procedures challenging too. It is a real shame that only half the available screen area is given over to seeing menu arrangements, too.

There is no doubt that the Polar RS800CX with S3 Stride Sensor is one of the most powerful computers out there. It could be too sophisticated for many beginners to feel comfortable with, but it has enough features to help get anyone who is serious about their training to the peak of performance. You’ll just have to live with its foibles.


  • Brimming with features
  • Modular components so you can use it for multiple sports
  • Can be used with three pairs of shoes (and three bikes too)
  • Comes with desktop software for analysis and configuring training sessions


  • Difficult to read the screen
  • Fiddly to get to grips with
  • Expensive – though two people could share one computer

Manufacturer: Polar


  • RS800CX £369.50
  • RS800CX Bike £379.50
  • RS800CX Run £464.50
  • RS800CX Multi £464.50
  • S3 Stride Sensor £125.00