Smartwatches with heart-rate monitors are becoming more prevalent with every passing year, and many advertise themselves as fitness trackers, but are they worth the investment?
Wrist-worn heart-rate monitors measure your pulse by shining light into the blood vessels in your wrist, and then detecting the changes in blood volume that occur each time your heart beats and pushes blood through your body. This way of measuring heart rate becomes increasingly inaccurate when people move around a lot (like when they exercise), because factors such as environmental light and the movement of a person’s muscles can interfere with the readings. Most companies have developed algorithms that cancel out a lot of the “noise” generated by people’s movements, but once the wearer passes about 80% of their maximal heart-rate, most trackers are completely inaccurate.
“In the new study, Dr. Marc Gillinov (a cardiac surgeon at Cleveland Clinic) and colleagues tested the wrist-worn heart-rate monitors on four devices: the Apple Watch, the Fitbit Charge HR, the Mio Fuse and the Basis Peak.
Each of the 50 healthy adults wore two trackers at a time (one on each wrist) while walking on a treadmill at different speeds, from 2 mph up to 6 mph (3.2 to 9.7 km/h). The participants also wore a device from fitness tracker company Polar, called the H7 chest strap monitor, as well as electrodes used for a standard electrocardiogram (EKG) test, which also monitors the heart’s electrical activity.
The measurements from the Polar chest strap and EKG were nearly identical, but the wrist-worn heart-rate monitors were not as accurate.
Of the four wrist-worn monitors, the Apple Watch and the Mio Fuse did the best. Most of their measurements fell within a range of 29 beats per minute (BPM) under the measurements from the EKG to 27 BPM above it. In contrast, the Fitbit Charge HR had measurements that ranged from 39 BPM under to 34 BPM above the measurements from the EKG, and the Basis Peak had measurements ranging from 33 BPM under to 39 BPM above the measurements from the EKG.
The Charge tended to underestimate heart rate, while the Peak tended to overestimate heart rate, the researchers noted. In general, the wrist-worn monitors were most accurate when the person was at rest, and their accuracy diminished as the wearer’s activity level increased, the researchers said.”
Wrist-worn heart-rate monitors are a new craze, but right now there isn’t enough scientific evidence on the accuracy of their devices. Every company who sells smartwatches has a webpage stating these inaccuracies (for liability reasons) but none of them are easy to find. Unless you’ve specifically googled (smartwatch name) accuracy, you’ve more than likely never seen these disclaimers before.
From Apple’s Website:
“Many factors can affect the performance of the Apple Watch heart rate sensor. Skin perfusion (or how much blood flows through your skin) is one factor. Skin perfusion varies significantly from person to person and can also be impacted by the environment. If you’re exercising in the cold, for example, the skin perfusion in your wrist might be too low for the heart rate sensor to get a reading.
Permanent or temporary changes to your skin, such as some tattoos, can also impact heart rate sensor performance. The ink, pattern, and saturation of some tattoos can block light from the sensor, making it difficult to get reliable readings.
Motion is another factor that can affect the heart rate sensor. Rhythmic movements, such as running or cycling, give better results compared to irregular movements, like tennis or boxing.
If you’re not able to get a consistent reading because of any of these factors, you can connect your Apple Watch wirelessly to external heart rate monitors such as Bluetooth chest straps. Learn how to pair Bluetooth accessories.”
From Fitbit’s Website:
“As with all heart-rate tracking technology, whether a chest strap or a wrist-based sensor, accuracy is affected by personal physiology, location of wear, and type of movement.
When you’re not exercising, wear your device a finger’s width below your wrist bone. Fitbit’s PurePulse heart-rate tracking system is designed to be most accurate when the device is worn on the top of your wrist. […]
With high-intensity interval training, P90X, boxing, or other activities where your wrist is moving vigorously and non-rhythmically, the movement may prevent the sensor from finding an accurate heart rate. Similarly, with exercises such as weight lifting or rowing, your wrist muscles may flex in such a way that the band tightens and loosens during exercise.”
From Samsung’s Website:
“Caution! The information gathered from Samsung devices and/or related software is not intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment or prevention of disease. The accuracy of the information and data provided by these devices and related software, including heart rate readings, may be affected by factors such as environmental conditions, skin condition, specific activity performed while wearing the device, settings of the device, user configuration/user provided information, sensor placement, and other end-user interactions. Please refer to the user manual for each device for more information on proper wear and use.”
From Garmin’s Website:
“Garmin wearables are intended to be tools to provide you with information to encourage an active and healthy lifestyle. Garmin wearables rely on sensors that track your movement and other metrics. The data and information provided by these devices is intended to be a close estimation of your activity and metrics tracked, but may not be precisely accurate. Garmin wearables are not medical devices, and the data provided by them is not intended to be utilized for medical purposes and is not intended to diagnose, treat, cure, or prevent any disease. Garmin recommends you consult your doctor before engaging in any exercise routine.”
In short, if you’re thinking of buying a smartwatch specifically for it’s heartrate monitoring, you might want to reconsider. Heartrate chest straps like Polar and Myzone will give you more accurate readings (and thus calorie burn readings) and normally cost less (from $80-$120 total cost depending on brand and sales). If you’re interested in using a smartwatch for more than just heart-rate they can be great pieces of technology, but if you’re only interested in the fitness aspect I’d recommended investing in a chest strap.
Below are some of the most popular smartwatches on the market right now – if you have any questions or are seeking a recommendation, feel free to contact us!
Series 4 (GPS + Cellular) Features:
- LTE and UMTS
- Built-in GPS, GLONASS, Galileo, and QZSS
- S4 with 64-bit dual-core processor
- Capacity 16GB1
- Optical heart sensor and Electrical heart sensor
- Improved accelerometer up to 32 g‑forces
- Ambient light sensor
- LTPO OLED Retina display with Force Touch (1000 nits)
- Ion-X strengthened glass
- Sapphire crystal and ceramic back
- Wi-Fi (802.11b/g/n 2.4GHz)
- Bluetooth 5.0
- Built-in rechargeable lithium-ion battery – Up to 18 hours of battery life
- Water resistant 50 meters
- Compatibility: Apple Watch Series 4 (GPS + Cellular) requires an iPhone 6 or later with iOS 12 or later. Apple Watch Series 4 (GPS) requires an iPhone 5s or later with iOS 12 or later.
- Sensors & Components:
Optical heart rate monitor
Relative SpO2 sensor
NFC (in special editions only)
- Display: Touchscreen, Grayscale OLED
- Fitbit Charge 3 has a battery life up to 7 days
Battery type: Lithium-polymer
Charge time (0-100%): Two hours
- Radio transceiver: Bluetooth 4.0
- Fitbit Charge 3 is water resistant to 50 meters.
- Compatibility: Syncs with iOS 9 and later, Android 5.0 and later and Windows 10 devices
- 270 mAh Battery
- Exynos 9110 Dual core 1.15GHz AP
- LTE: 1.5GB RAM + 4GB Internal Memory
- Bluetooth: 768MB RAM + 4GB Internal Memory
- 3G/LTE, Bluetooth®4.2, Wi-Fi b/g/n, NFC, A-GPS/Glonass
- Accelerometer, Gyro, Barometer, HRM, Ambient Light
- WPC based wireless charging
- 1.2” (30 mm) Circular Super AMOLED (360 x 360) Full Color Always On Display
- Corning® Gorilla® Glass DX+
- Compatibility: Samsung, other Android: Android 5.0 or higher & RAM 1.5GB above
iPhone: iPhone 5 and above, iOS 9.0 or above
*Activation feature for Mobile Network of Galaxy Watch with
Non-Samsung smartphones may not be available in some countries.
- Chemically strengthened glass lens
- 1.23″ (31.1 mm) diameter
- Display resolution: 215 x 180 pixels
- Display type: Sunlight-visible, transflective memory-in-pixel (MIP)
- Weight: 40.2 g
- Battery life:
Smartwatch Mode: Up to 11 days
GPS mode: Up to 14 hours
UltraTrac™ mode: Up to 24 hours without wrist heart rate
- Water rating: 5 ATM
- Compatibility: iPhone and Android