Fitness and health are now tracked continuously by watches and phones.

Today many people wear a smart watch or use an application which counts their steps, their sleep and their heart rate every day. In my opinion, this is mostly a positive development, although it also has some risks.

Firstly, these devices motivate people to move more. When a person sees that he walked only two thousand steps today, he feels that he must go outside, and a small goal like ten thousand steps is easy to understand. Many people who never did sport before started walking or running because of this.

Secondly, these devices can find health problems early. A watch can notice that the heart rhythm is not normal, and the person goes to the doctor before something serious happens. There are many stories about people whose life was saved in this way.

On the other hand, some people become too worried about the numbers. If they sleep badly for one night, they think they are ill, and this stress is worse for their health than the bad sleep. In addition, all this information about our body is collected by big companies. We do not know exactly who reads this data, and maybe in the future an insurance company will use it to increase the price for people who do not exercise.

In conclusion, I believe that health tracking is useful because it encourages exercise and can detect illness early, but governments should make strict rules about who can use this personal information.

Watches and phones now record steps, sleep, heart rate and much else continuously. I regard this as positive in its immediate effects, though the way the resulting data is held raises a concern that is easy to overlook.

The benefit rests on feedback. Most health behaviour suffers from a long delay between action and consequence — the effects of a sedentary decade are invisible until they are severe — and continuous measurement closes that gap by making an abstract risk immediately concrete. The clinical case is stronger still: devices detecting irregular heart rhythms have identified conditions in people who had no symptoms and no reason to seek testing, which is exactly the category of illness that is cheap to treat early and dangerous to discover late.

There are real drawbacks. A minority of users become preoccupied with their numbers, and monitoring sleep in particular can produce the anxiety that then damages it. There is also a tendency to optimise the metric rather than the health it represents — walking to complete a step count while ignoring diet, for instance — because the measured thing feels like the real objective.

The more serious issue is who holds the record. This is continuous medical information about millions of people, gathered by technology companies rather than health services, and therefore outside most medical privacy regulation. It is not difficult to imagine insurers pricing policies on activity data, or employers taking an interest in it, and consent given by accepting an application's terms is not meaningful consent to that.

In conclusion, I consider the trend positive for the individual user, since the health gains are concrete. The arrangement under which the data is collected, however, deserves considerably more scrutiny than it currently receives.

Continuous self-monitoring is worth judging in two parts, because the answers differ. As a tool in an individual's hands it is largely beneficial; as an arrangement under which a small number of companies accumulate clinical records on hundreds of millions of people, it is considerably harder to defend. My verdict is positive on the first and negative on the second, and the second is the one that will matter in twenty years.

The individual case rests on a specific mechanism: feedback delay. Almost everything that damages long-term health does so invisibly — the consequences of inactivity or poor sleep accumulate for decades before announcing themselves — and behaviour responds very poorly to consequences that distant. Continuous measurement substitutes an immediate signal for a delayed one, which is why devices change habits where advice does not. The clinical benefit is more direct still: detection of arrhythmias in asymptomatic people has identified serious conditions that would otherwise have surfaced as a stroke, and this is the category of illness where early discovery matters most.

The costs to users are genuine but narrower than commonly claimed. A minority develop real anxiety around their metrics, and sleep tracking is notably self-defeating, since worrying about a sleep score reliably worsens sleep. More interesting is goal displacement: the measure becomes the objective, so a user completes a step count while eating badly and counts the day a success. False positives compound this, sending healthy people into medical systems for reassurance about a reading no clinician requested.

What concerns me far more is the custody of the data. This is continuous physiological information — activity, heart rate, sleep, in some cases location and menstrual cycles — held by consumer technology firms rather than health providers, and therefore governed by terms of service rather than by medical privacy law. The consent obtained is consent in name only: nobody reads it, and nobody could meaningfully anticipate the uses to which a decade of such data might be put. The plausible ones are not exotic. Insurers pricing on activity, employers inferring health status, or a company changing its policy after acquisition all follow naturally from data existing in a place where it can be used.

My conclusion is therefore split, and deliberately so. The technology is good and I would not discourage anyone from using it. What deserves objection is the de facto decision to build a population-scale medical database outside medical regulation — a choice nobody voted on and which is far easier to prevent now than to unwind later.