Optical heart rate monitors on the latest running watches and fitness bands have got a bit of a bad rap, but in reality, the choice between strap and wrist isn't black and white. For many people chest straps are a no-go and even they can't provide spot-on accuracy.
Essential reading: Heart rate variability explained
We've spoken to experts the world over and tried out all the latest devices, and can now offer some pretty clear advice on the matter. Unfortunately, there's not a definitive answer without caveats – but we can arm you with the facts about a pretty impassioned area of technology.
Both wrist and chest strap devices technologies use algorithms to convert what they read into estimated heart rate but the theory is that, because chest straps track closer to the heart, they tend to be more reliable – provided you've got a good wet contact between the pads and the skin.
Must read: Re-live James' heart rate training diary
Because they're on your wrist, optical heart rate sensors actually read your blood flow further from the source and accuracy can also be reduced by light leaking in and affecting the sensor, the movement of your arm and the flexing of your wrist.
That said – for many optical is good enough. In our testing the TomTom Spark and Garmin Vivoactive HR both matched a chest strap for running accuracy, all the way up to HIIT training, when the differences really told.
It's important to remember that any non-invasive sensor will have accuracy issues, even the ones used in sports science labs. While chest straps generally boast reduced lag times, more data points and a better position on the body, they're far from immune to drop-outs.
Our advice is that steady runs are adequate with optical tech, but if you're venturing into HIIT or gym work, chest straps are the way to go.
Winner: Chest strap
The chest strap gets a hard time when it comes to comfort. Anyone who's ever run for more than an hour wearing one will attest, they can get a bit chafey, they feel restrictive and some people find it a bit hard to breathe.
It's also true that wrist-based heart rate watches tend to need to be done up tight on the wrist and can be uncomfortable over long training sessions but on the whole, the watches offer a happier fit.
Also we need to address The Boob Problem. Let's make one thing clear, I don't have boobs. But I have spoken to a lot of people who do and, more often than not, they only have negative things to say about chest straps. That said, the MyZone MZ-3 chest strap has an optional bra accessory, to try and mitigate the problem.
Okay that's not actually a word but chest strappers will be all too familiar with what it means. You get to the gym and dig around in your bag only to find your HRM is nowhere to be found.
You're sure you put it back in after last night's session but then you did also empty out your gym kit and there's a good chance it'll be lying sweatily on top of your wash basket at home.
If you use a sports watch there's still chance you'll forget it – but if that watch is part of your daily life, it's more likely to be there when you need it.
HRM chest straps rely on old school watch batteries and while battery life can vary – something like the Polar H7 will give you a quoted 350 hours of tracking, definitely out lasting all optical heart rate watches on the market.
However, it's vital to remember to unclip it the unit from the strap. Fail to do this and your chest strap will sit in your bag or drawer having the life sucked out if it.
Optical heart rate monitors, on the other hand, will only give you half a dozen sessions or so, depending on how you use them when you're not training.
More frustrating is that almost all of them have their own unique charging cradle that means you either have to remember to charge them at home overnight or cart the charging cable with you wherever you go. Both of which you will almost certainly forget to do at some point.
Winner: Chest strap
Dispute their accuracy if you like, but wrist-based trackers almost always find a pulse. Provided you've got one, the optical heart rate sensors will pick it up and display this piece of tech success conveniently where you can see it.
In contrast, Bluetooth chest straps don't always hook up seamlessly to your smartphone or the watch you're using. The worst thing here is that when it fails you're not quite sure if it's the Bluetooth playing silly buggers or the battery in the sensor has called it quits.
What ensues is a period of Sherlock Holmes detection to decipher what the hell is happening. And all too often the case remains unsolved.
HRM chest straps can offer a cheaper way to monitor heart rate, particularly if you opt for a Bluetooth device that'll partner with a range of fitness tracking apps to give you a sweet of insights that can match a lot of the cheaper watches.
Winner: Chest strap
Chest Strap HRM vs Wrist OHR: Verdict
For those of you who've been keeping score you'll notice the contest has ended all square. That's just a cop out right?
Well, yes and no. Different people will read it different ways. Many Wareable readers will stop reading at accuracy – and that's fine. If you're tracking a workout, you want it to be as definitively accurate as possible. But for others, the thought of training with a strap is just too off-putting.
The fact is that optical is workable. And be honest about how you use the data. Most current optical devices are fine at a steady pace. What's more, if you're only using your chest strap for 25% of your workouts and aren't really using that data meaningfully, isn't it better to use a more convenient device?