Heart rate (HR) monitors are valuable devices for fitness-orientated individuals. There has been a vast influx of optical sensing blood flow monitors claiming to provide accurate HR during physical activities. These monitors are worn on the arm and wrist to detect HR with photoplethysmography (PPG) techniques. Little is known about the validity of these wearable activity trackers.
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These devices also are multifunctional and some offer GPS, messaging, and cell phone capabilities. The more functionality the higher the price. There are wrist monitors that only provide heart rate.
Fit is extremely important since exercise running, treadmill or bicycle training can affect accuracy.
Health Train recommends an in-person trial for fit, appearance, and accuracy, before buying online.
The current study investigated the accuracy of six newly released wearable activity trackers that continually measure HR with PPG techniques through the arm and wrist area during rest (3 min seated before and after the experiment), and specific treadmill speeds. The criterion measure was a Polar RS-series chest strap with wrist receiver, which in earlier studies was found to have good criterion-related validity with the ECG, and was well suited for measuring HR during PA and exercise training.8 11
Only a few studies have evaluated the accuracy of HR monitors. In a 2002 study using traditional chest strap HR monitors, investigators found that correlation with the ECG decreased with a higher speed of 9.6 km/h and the investigators attributed this to increased upper body movement.2 A similar study conducted in 2011 involving the Smart health watch, an activity monitor that relies on two points of contact to measure the heart's electrical impulse, had comparable results. The researchers validated the HR for the Smart health watch at rest and during treadmill activities, but reported that at higher speeds of 7.2 and 9.6 km/h the watch had reduced ability to detect HR (a decrease of 6% and 13.9%, respectively).12 Again, the investigators attributed this reduced ability to increased upper body movement.
Conversely, in the present study, the accuracy of the optical sensing HR activity monitors had the least MAPE during the highest speed tested, 9.6 km/h. During this phase, the greatest MAPE observed was with BP (3.28%) and MB (3.06%). These results mirror those found in a recent, small study that evaluated the performance of the MA and SR using an ECG as the criterion measure.9 The investigators reported the MAPE of the MA for walking and running was 5.60% and 2.37%, respectively. In the present study, the MAPE of the MA was 8.02% and 1.15%, respectively. In the past study, the MAPE of the SR for walking and running was 10.49% and 3.81%, respectively. For the present study, the MAPE of SR was 5.40% and 2.91%, respectively. Both studies showed a reduction in MAPE with increased speed. One possible explanation is that with increased intensity there is improved perfusion, which could decrease the error rate.
Overall, strong correlations were observed between the activity monitors and the criterion measure, ranging from r 0.87 to 0.96, and the measured HR from all six monitors were significantly equivalent to the measured HR from the criterion measure is resting, walking and running conditions. This suggests that all the activity monitors would provide comparable accuracy to the more established HR monitor. This is an important finding since it informs the existing literature on HR monitoring devices and also supports the utility of these new devices for everyday personal use as well as for research applications.
While conducting the experiment, challenges with correct fit and placement were observed. While great care was taken to ensure watches were placed properly, the experiment was conducted in semi-free-living conditions which resulted in realistic issues arising. A few of the participants had either larger or smaller wrists and forearms that made the proper fitting of the activity monitor a challenge. However, all watches were fitted according to the manual specifications with maximum effort focused on placement control of the watches. In this study, when some participants tried to hold the treadmill railing, HR readings sometimes became irregular, and in two incidents, the BP and FH did not provide an HR reading. The MA also was observed to fluctuate between a high and low HR during this time. Once the participant began walking naturally, with arms swinging, HR readings more closely reflected the criterion measure. Similarly, as soon as the participant started jogging, the arms bent at the elbows and became perpendicular to the body. During the 6 mph jogging phase, the MA and TT had <1% MAPE while the FH was observed with its lowest MAPE for all the protocol intensities. It is speculated that the lesser MAPE is likely attributable to the arms being in a bent, stabilized position combined with the increased HR from exertion. Perhaps a higher and stronger HR can be ‘read’ more easily by the LED lights.
The strengths of this study included a reasonable sample size, examination of a variety of wearable activity HR trackers that are currently available in the market, and utilization of a mixture of various walking and running intensities. In addition, proper fit and constant supervision provided the best opportunity for activity tracking as each tracker was functioning within its intended capacity. The result of this study adds to the existing literature on HR monitoring and is one of the first to undertake validation of new PPG optical sensing HR activity trackers. However, it does have some limitations. The sample population included only healthy, younger individuals (19–45 years) who engaged in regular aerobic exercise and were within the normal range of body weight and body fat. Generalizations cannot be made for youth and/or older adult age groups or for individuals of other body sizes. This study included only walking and running activities; it could be possible that during intermittent or high-intensity interval training results could have been different. The study was also conducted using a controlled treadmill protocol and the transfer of results to free-living conditions should be made with caution.
In conclusion, the present study results showed favorable outcomes for the six PPG optically sensing HR wearable activity trackers that were tested at rest, and during treadmill walking and running in a healthy sample population. Good criterion-related validity was found between all monitors and the Polar HR monitor. In addition, the wearable activity trackers were deemed accurate for the recreational athlete and for research purposes. Furthermore, wearable activity trackers utilizing built-in PPG HR sensors have the potential to overcome the limitations of the traditional chest strap and to advance the science and practice of PA assessment. Further tests utilizing a fixed floor, such as a track, and various indoor/outdoor environments and high-intensity exercises (including weight lifting and bicycling) could confirm the usability of these wearable trackers in expanded exercise settings. Future studies should include different populations and health concerns, such as young and older adults and individuals afflicted with obesity (ie, epidermal thickness) and diabetes (ie, poor blood circulation)
How accurate are the wrist-based heart rate monitors during walking and running activities? Are they accurate enough? - Abstract - Europe PMC:
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