can we trust the dimensions of the connected watches?

Not all smartwatches are created equal. The smallest recommended models produced absolutely remarkable readings: they exceeded the heart rate by 50% and counted to double the number of steps walked. But some watches – from the ranks of Garmin, Coros, Fitbit, Apple or Samsung, for example – offer more accurate measurements. Is that enough to help us in our search for better iron shape and health?

Here’s a snapshot of the services, all in all fairly modest, provided by today’s very best models. Over the next few years, their abilities should improve at a relatively slow pace with their technological advances and a more peaceful pace of medical study. They make it possible to identify their strengths and identify their weaknesses, which manufacturers strive to improve.


In order to follow the evolution of our physical form, it is better to avoid examining too closely the dimensions of connected watches: their accuracy is very relative. They probably exaggerated the number of steps walked in a day, noticing phantom steps when lying down or sitting. All you have to do is fold the laundry for five minutes, without ever moving your legs, for a hundred phantom steps to add to the daily count.

Under these conditions, it is better to avoid giving too much importance to small differences in flow from one day to the next. Note, to reduce the number of phantom steps, it is better to wear the watch on the non-dominant arm-the left if you are right hand.

Does this activity number, brought to our attention, really inspire us to improve our form? The research is contradictory: an Australian study reported a real increase in daily steps, but a study from the University of Florida points out that smartwatches rarely cause weight loss.

The key may come from a long follow-up, accompanied by a doctor, because owners of connected watches are sometimes likely to leave them, like American journalist Lindsay Crouse: [A cause de ma montre], Exercise no longer helps me push the pressure: it adds to it ”, he wrote. Activity tracking can also lead to a bad experience of addictive behavior. Not all personalities are good with watches.


Many smartwatch models provide a daily estimate of calories consumed. In an ideal world, this should be made possible to match energy expenditure with calories consumed during a meal. But these estimates are wrong, according to a broad consensus in the scientific community. The measurement of energy expended is estimated and the knowledge of the wearers of the watch is incomplete-the amount of fat mass and specific metabolic characteristics will vary in particular from one person to another.


Smartwatches are a great helper for runners, but athletes looking for performance should treat them with caution, as their accuracy is not perfect. The best watches sometimes rate distances with a deviation of two or three percent. As long as they are equipped with GPS, their wanderings are clearly visible on the map: their route will pass through roads and rivers.

The most advanced models are reliable enough to read the heart rate during a run of a steady run, but during intermittent training the rate usually rises to twenty beats above the actual rate. These deviations are tolerable, except for a top athlete.

Read our guide on the topic: The most connected running watches
A fourth generation smartwatch from Apple.


Tracking bedtime is pretty good for people who fall asleep right away on contact with their pillow – except for occasional mistakes. But smartwatches tend to overestimate the nights people stay in for long periods of time before bed.

Worse: their measurements were completely wrong when they claimed to identify phases of deep and paradoxical sleep-which still today require heavy equipment, capable of measuring brain waves, eye movements, the amount of inspired air, and so on. For now, it’s best to avoid relying on connected watches that claim to provide a mark on sleep quality.

In addition, research has found many cases of patients viewing these sleep measurements obsessively, increasing their stress levels to the point of interrupting their nights, rather than improving them. An English study from Oxford University focused on the psychological risks of a poor sleep symptom, which is likely to promote the feeling of tiredness felt and lead to a negative spiral.


Currently, connected watches detect very few diseases. Their ambition primarily focuses on respiratory and cardiovascular pathologies, with relative use.

This disease affects 4% of the population, it is diagnosed in only 20% of patients and can cause severe heart failure. Connected watches more often have an oximeter that makes it possible to measure oxygen droplets in the blood.

After a night of frequent falls, most watches are careful not to launch an “apnea alert”. It is up to the user to consult the oxygen curves at night and interpret them, which is difficult, especially since the measurements are difficult to do correctly and their accuracy falls short for some people. Many manufacturers insist that these measurements should not be used for medical purposes.

The Scanwatch watch from the Withings brand is more ambitious: it gives an indication of respiratory disturbances at night (low, medium or high). In 2020, Withings also launched a study comparing apnea detection on its Scanwatch to laboratory equipment.

However, this study disappeared in 2021 from its page referring to the scientific work being done. According to a spokesman Withings contacted by The world, the study is still ongoing, with no known date of its conclusion. The brand has determined that it continues to improve its algorithms.

The Withings Scanwatch is one of the few watches that sends an alert in case of arrhythmia, like the Apple Watch, which also issues an alert when the heart rate slows too much or speeds up too much. Unfortunately, this surveillance only makes it possible to detect a very small proportion of cardiovascular diseases, as specified in world in 2018 Philippe Steg, head of the cardiology department at the Bichat hospital.

In very rare cases, these watches can save lives. However, for every life saved, they encourage other patients to engage in risky treatments unnecessarily. Or, worse, they can give some a false impression of protection, pushing them to ignore the physical feelings that would have led them, in normal times, to consult for, for example, in a heart attack, a relatively frequent pathology.

According to various cardiologists, however, connected watches may be reasonable for daily monitoring of patients with known problems, especially the elderly, or patients with risk factors such as tobacco, alcohol, hypertension, diabetes. , cholesterol, overweight.

Read also The new Apple Watch: a “footnote on cardiovascular prevention”
An Apple Watch, the brand that sells the most connected watches.

Does the oximetry sensor that detects respiratory failure, combined with other sensors present in some watches, make it possible to diagnose Covid-19 early enough for the person to be able to isolate themselves on the left? still infectious? It’s not certain, according to a Dutch study: it’s probably too late to detect. Also, smartwatches are likely to confuse Covid-19 with other illnesses such as the flu.

These watches can, however, be useful when the disease erupts, to monitor oxygen levels and alert a doctor if hospitalization is needed. But there are other, safer, handheld devices that measure oxygen at the tip of the finger that were distributed to U.S. patients during the pandemic.

Leave a Comment