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Jump to Key Points Data from wearable devices do not replace a clinical examination, but they can serve as a useful starting point. At the 19th National Congress on Sports Medicine and Traumatology, a medical meeting in France, Stéphane Doutreleau, MD, PhD, Grenoble Alpes University Hospital, La Tronche, France, helped the audience distinguish between an artifact and a true arrhythmia.
Reliability Depends on the Device and the Activity
The chest strap, which records an electrical signal, remains the gold standard among consumer devices. It generally provides a reliable measurement of heart rate, although electromagnetic interference or artifacts may occur. Optical sensors in watches and wristbands, based on photoplethysmography, are more comfortable but more sensitive to movement, sensor positioning, sweat, and the type of exercise (see Table).
Table. What types of wearable devices are available for heart monitoring?
| Object type | Technology | Reliability | Benefits | Disadvantages |
| Chest belt | ECG | Very high | Accuracy, minimal interference | Less practical, requires an accessory |
| Smartwatches | PPG | Variable | Practical, multifunctional | Less reliable when moving (underestimation of heart rate) |
| Optical bracelets | PPG | Average | Lightweight, discreet | Sensitive to movement |
| Connected headphones | PPG | Average | Discreet integration | Limited reliability |
| Sensors integrated into clothing | PPG/ECG | Variable | Comfort, discretion | Not widely available, high cost |
| Smart toilets | PPG/ECG (experimental) | Unknown | Originality | Impractical, compromised privacy |
| Connected Holters | Medical ECG | High | Continuous monitoring | Requires medical monitoring |
| PPG = Photoplethysmography | ||||
At rest or while walking, optical measurements are often satisfactory. However, during running, cycling, or activities involving frequent wrist movements, the discrepancy with a chest strap can become significant. Heart rate is then most often underestimated, sometimes by several dozen beats per minute. Performance also varies by brand and model. “It is therefore essential to know what device is being used before assigning any clinical significance to the displayed data,” Doutreleau said.
- Chest strap ECG = highest reliability; smartwatch PPG variable, motion-sensitive.
- Running/cycling often ↓ watch HR; underestimation may reach several dozen bpm.
- Isolated HR spikes may reflect true arrhythmia, not artifact; correlate with symptoms.
- HRV useful only at rest, standardized, serial measurements; single value low utility.
- Wearable data guide evaluation, never replace exam; extreme values need medical confirmation.
Furthermore, watches may also automatically adjust certain parameters — particularly maximum heart rate — after an isolated spike. This value should not be accepted without verification: An artifact or arrhythmia can cause the device to recalculate an erroneous maximum heart rate and skew subsequent training metrics.
Do Not Dismiss Heart Rate ‘Spikes’ as Insignificant
Irregularities observed on heart rate monitor graphs are often attributed to interference. However, a spike may correspond to a genuine arrhythmia. Premature beats or certain arrhythmias can temporarily alter the intervals between heartbeats and result, as recorded by the device, in a very brief increase in heart rate. Data collected simultaneously by a heart rate monitor and a Holter monitor have thus shown that a significant proportion of these anomalies were not related to interference.
In practice, an unusual waveform must be evaluated in light of the symptoms, the circumstances of its occurrence, and the type of sensor used. Palpitations, a very high heart rate, a feeling of discomfort, unusual exercise intolerance, or a marked deviation from the usual pattern warrant caution against jumping to the conclusion that it is simply a measurement error. Confirmation via ECG, Holter monitoring, or another medical device may be necessary. Some portable systems now allow for the recording of an ECG, either when symptoms occur or on a more continuous basis, which can facilitate the diagnostic process.
Heart Rate Variability
Heart rate variability is easily accessible on many watches, but its interpretation requires rigor. Ideally, it should be measured at rest, under standardized conditions, always using the same device. For athletes, a protocol may include a measurement lasting a few minutes while lying down, followed by a measurement after actively standing up. This variability is influenced by numerous factors: fatigue, sleep, stress, temperature, respiratory rate, meals, hydration, noise, light, and recent activity. A single measurement therefore has little value. It is preferable to track a trend, with several weekly measurements taken under comparable conditions, and to consider the patient as their own control.
A persistent decrease in variability — especially when accompanied by an elevated resting heart rate, significant fatigue, or decreased performance — may suggest insufficient recovery or excessive training load. Conversely, a lower resting heart rate combined with stable or increased variability may indicate a favorable adaptation. However, these indicators remain nonspecific and must always be interpreted in conjunction with symptoms, clinical examination, and training context.
A Guide, Never a Substitute for Clinical Evaluation
Wearable devices can provide valuable information on heart rate behavior during exercise and at rest. In particular, they can raise suspicion of an abnormal chronotropic response, an exercise-induced arrhythmia, or an unusual inability to increase heart rate and can also aid in monitoring internal load and recovery, even though these indicators are based on calculations that are sometimes complex and vary from one device to another.
It is therefore essential to adopt a critical and pragmatic approach: ask which device was used and under what conditions, verify the consistency of the measurement, look for associated symptoms, and compare the data with the patient’s usual values. Connected data are particularly useful when integrated into a clinical history, but they should never be interpreted in isolation. In the event of an extreme value, an unusual waveform, or suggestive symptoms, it is better to confirm the data through an appropriate medical examination than to dismiss them as a mere artifact.
This story was translated from JIM, part of the Medscape Professional Network.
