These “smart” watches are used by 27% of French people and purchasing intentions remain strong (source 1). The latest models multiply health functions, but are they really useful?
What is a smartwatch and what does it measure?
Heart rate
They continuously measure the number of heartbeats per minute by detecting pulsations at the wrist. “It is quite reliable and useful because the heart rate at rest is a good indicator of cardiovascular health, to be compared to the norm depending on one’s age. A high heart rate or ‘tachychardie‘ (beyond 100 at rest) for no reason can also indicate a rhythm disorder, to be confirmed with a cardiologist,” notes Dr. Sana Amraoui, cardiologist, head of the rhythmology department at the American Hospital in Paris. The watch also calculates our maximum heart rate (max HR) : a guide to staying at the right intensity during physical activity sessions.
Number of steps and level of physical activity
“Even though there may be an error of 10 to 20% in the number of steps measured, it does not matter: studies show that this encourages you to move more and has a beneficial impact on the level of physical activity », summarizes Dr Nicolas Postel-Vinay, doctor at the Arterial Hypertension Unit at the European Georges Pompidou Hospital (Paris). They also detect if you stay still for too long and send alerts inviting you to walk for a few minutes: useful to fight against sedentary lifestyleespecially if you work seated.
Sleep
Specialists agree that these data are still approximate : the watch has difficulty distinguishing rest time from real sleep time, and the different sleep phasesespecially if we move little. “This analysis is never enough to make a diagnosis or rule out a sleep apnea if, despite a good score, you wake up tired: you must always confirm with a doctor,” insists Dr. Amraoui. And this surveillance must not turn into obsession : avoid sleeping with your watch on if you are already anxious, as this can paradoxically increase the fear of sleeping poorly and interfere with sleep.
Connected watch: which health measurements are really useful?
Heart rhythm with electrocardiogram (ECG)
Two electrodes – one on the wrist, the other at the level of a button or the metal contour of the watch – measure electrical activity of the heartfor thirty seconds. Algorithms evaluate rhythm variations and send an alert in the event of repeated irregularities (source 2). « Although it is not as precise as a ECG medical, it is 90-97% reliable if the bracelet is well adjusted. This measure can really help detect arrhythmiasparticularly atrial fibrillation, which is common (1 in 4 people over 40) and increases the risk of stroke or heart failure, even when there are no symptoms. Also practical for establish a diagnosis in case of palpitationsbecause at the time of the consultation, patients often have a normal rhythm,” observes the cardiologist.
She recommends a watch equipped with the ECG function if you have a tendency to palpitations, cardiovascular risk factors (history of stroke or heart attack, hypertension, diabetes, smoking, etc.) or over 55 years of age.
Heart rate variability
Some watches measure microvariations in the gap between two heartbeats, which allow the heart to adapt when it needs to speed up or slow down. » It is a good indicator of the level of stressbecause heart variability decreases when we are anxious or depressed. The interest is above all that the watch invites you to take breaks and do small breathing exercises type cardiac coherencebeneficial for lowering cardiovascular risk,” notes Dr. Amraoui.
Connected watch: which measurements are unreliable or useless?
Blood pressure
Most watches use optical measurement (PPG), which only gives an estimate, not an actual value. An exception: the Huawei Watch D2equipped with an inflatable balloon to compress the radial artery, with a precision comparable to a wrist blood pressure monitor. “There is no point in measuring your blood pressure continuously: when you have to monitor it, it is better to do it sitting quietly, and use a blood pressure monitor on the arm, the only one recommended (we find them from €15),” says Dr Postel-Vinay.
Body temperature
The body temperature varies constantly if only depending on the outside temperature, after exercise… the oxygen level in the blood (Sp02): the reliability of the measurements is, for the moment, disappointing.
Connected watches: the flagship models and their benefits
- L’Apple Watch SE 3 (269 €) : personalized heart rate zones to adapt your sports sessions, and the very visual “Activity” rings which encourage you to move more;
- The Withings ScanWatch2 (€349.95) : the ECG on the wrist and the possibility of having it analyzed by a cardiologist (Cardio Check-Up offered with a free one-month subscription to Withings+);
- Garmin’s Vívoactive 6 (€329.99) : measurement of heart rate variability and autonomy of up to eleven days without recharging.
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