Even cheap fitness trackers now have an optical sensor for the heart rate in everyday life and during sports on board. Is it still worth buying and using a classic heart rate monitor on the chest strap? What are the pros and cons? What should you consider when buying? We provide the answers in our buying advice.
Optical heart rate monitors and chest straps – how they work and the differences
Let’s first address the question of how optical heart rate monitors and chest straps work at all, and how they detect the user’s heart rate – because that’s where the main differences between the two variants lie.
Optical heart rate monitors are located on the underside of the housing for fitness trackers (best list), sports watches (best list) or smartwatches (theme world). They lie directly on the skin and measure the user’s heart rate. Two or more LEDs illuminate the blood vessels on the wrist. The light is then either reflected or absorbed according to the amount of blood volume passing through the vessels. The optical sensor perceives these changes in light and uses them to calculate the heart rate. Current units measure the pulse either continuously or at such short intervals that it almost comes close to permanent measurement.
The sensor on the chest strap does not determine the heart rate by measuring blood volume, but by measuring the electrical activity of the heart. To do this, it measures the corresponding signals and then converts them into data for pulse indication. Chest straps measure heart rate with ECG accuracy. Therefore, they are still the preferred means of professional training or medicine.
Optical heart rate measurement: pros and cons
The great advantage of optical heart rate measurement is that no additional hardware is required. It does not matter if they are cheap devices like Xiaomi Mi Band 6 (test report) or advanced watches like Apple Watch Series 6 (test report) – they have everything they need to collect the data on the wrist. The processing takes place directly on the device, apps on the mobile phone usually enrich the data further and provide additional information. The tracks also provide data on lap times and effort and can be programmed, at least in part, with training plans or record the route traveled via GPS.
The first thing that stands out among the disadvantages is the significantly shorter battery life and the less accurate measurements. The latter is amplified by interfering factors, such as when the watch does not tighten enough or slips during running. In our numerous tests, we have also noticed that the measurement on the wrist always fails (or at least becomes significantly less accurate) when we practice sports with strongly varying heart rate frequencies. Strength training, HIIT or martial arts are examples of this.
In addition to optical heart rate sensors, which are integrated in conventional sports watches and fitness trackers, as well as chest straps with heart rate sensors, there are also a number of special models. With Variety Sense, for example, Polar offers an optical sensor that works independently of a sports watch and is not worn on the wrist, but on the upper arm. Therefore, this sensor is particularly suitable for swimming or sports where watches on the wrist tend to be annoying (e.g. kettlebell or martial arts). We have tested Polar Variety Sense thoroughly and reveal in the test who this sensor is particularly suitable for.
Basically, because sports watches with optical sensors usually have a wide range of other smart features, they often cost many times as much as a chest strap. Excluded from this are fitness trackers, which like chest straps are already available in the price range from around 30 euros.
Heart rate measurement with a chest belt: advantages and disadvantages
As mentioned in the beginning, the breasts do not measure the electrical activity of the heart optically, but directly. This provides high accuracy in all sports. Another advantage is the long operating time that a heart rate monitor can pull out of a battery or rechargeable battery. The data is transmitted, for example, to a watch, a bicycle computer or a treadmill, either via a proprietary radio standard, via the somewhat more open Ant + standard or via Bluetooth. The latter allows, for example, a mobile phone to record the data directly. However, some sports watches, such as those from Garmin, Pulsar or Suunto, may have access to heart rate belt data in addition to their own measurements.
Ant + used to be the preferred standard, but now you see it less and less – smartphones hardly use it anymore. A proprietary radio usually works only between certain devices from the manufacturer or, especially with cheap products, only with a fixed pair of devices.
Another disadvantage is that a heart rate monitor can quickly become uncomfortable, especially for endurance sports. It depends on the model, in some cases the straps can be replaced for greater comfort.
There are also chest straps that come with a matching watch. This includes PC 15.11 from Sigma Sport. This is a classic digital sports watch without smart functions, which measures the heart rate using a chest belt and offers additional functions such as display of the intensity zones including a zone alarm, a calorie counter and display of the training duration per. intensity zone. The advantage of this watch is that it is very inexpensive compared to traditional optical sensor sports watches and combines the benefits of ECG accuracy with the independence of external hardware.
Chests from well-known brands such as Polar and Garmin are available from a road price of around 55 euros. Polar Variety Sense costs a little more and is just under 90 euros. Depending on the model, sports watches are available with a usable optical sensor from around 150 euros – our buying guide for sports watches and fitness trackers will help you choose the right product.
If you are considering buying a chest belt or a fitness tracker with optical heart rate monitor to monitor your own heart rate, consider one main question: How accurate should the measurement be? Because the answer to this should determine which variant of heart rate measurement is best for you.
If you primarily want to keep an eye on your heart rate during endurance sports, where you are primarily active with a constant heart rate, you will not go wrong with an optical heart rate monitor. Most sports watches and fitness trackers offer sufficient measurement accuracy for these purposes, which usually differs only slightly from the results of a chest strap.
Athletes who value a high degree of accuracy, who want to train according to their heart rate (eg when running with basic endurance in mind), or who regularly train with strongly fluctuating heart rate values, prefer to wear a chest belt. Thanks to the ECG accuracy, the latter offers a maximum degree of precision and therefore responds quickly to changes in heart rate – which athletes depend on for certain types of training.