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There's a building tension. Apparent is the chilled vapour emanating from my competitors as they execute the "about to run" wiggle on the start line.

A rapid flick of the hips.

I'm at my local 5km community parkrun and I'm focused. Three, two, one...

Hold on. I have to sort my tracker. So does the guy beside me.

The person in the line sighs. I won't start until… yes! GPS ready, and I'm running.

Amidst the crowd, it's hard to find a person without a smartwatch on it. And it's not just us participants who use them.

We're witnessing a thriving, massive industry. Brands like Samsung Galaxy lead the market, featuring an wide array of various versions to cater to a spectrum of budgets. According to how feature-packed the watch you choose, prices can start from a hundred pounds to a significant investment.

"I find it infuriating, it's impossible to relax."

"It comforts me… It acts as a companion encouraging me."

"I wish it wouldn't say I've had a restless night."

A handful of the comments I've received from other tracker enthusiasts when I ask what they think of theirs.

The Data Dilemma

My current opinion on mine? Right now, irritating. It's reporting I'm not hitting my target, causing me to question whether the overhead branches along my route are interfering with my GPS connection.

Millions of us fasten these little gadgets onto our arms and keep them on 24/7, ostensibly at ease with the fact they're continuously recording us.

Long past are the days when we used them solely to give us an idea of our step count. Currently, they can analyse our sleep patterns, heart rate, glucose levels, our VO2 max.

It's a challenge to find a health indicator they fail to monitor.

But do they do what they say they do? And are the numbers we scrutinise a true reflection of our actual health? Do they boost our daily wellness, or do the multitude of readings and cheerleading alerts just increase our daily stresses?

A Love-Hate Relationship

"I do get a bit preoccupied with mine," a wearer reveals.

While she appreciates how her device monitors her runs, she finds some of its other features "excessive" at times - a feeling first discovered during a significant period.

Prior to discovering she could adjust the settings, her smartwatch kept telling her she was not being productive enough. Later on, the watch keeps telling her she's had a bad night's sleep.

"I have a young baby, there's no point to be informed I've not slept," she says. "That fact is all too clearly."

Why doesn't she just stop wearing it?

"I suppose I could, perhaps, but I have this complicated dynamic with it," she continues. "I love it for its exercise data, I sometimes question whether all the other things it can now do is perhaps overkill for me."

Inside the Device

Each model of smartwatch has its own unique way of monitoring your vitals and interpreting your data, but the vast bulk use sensors on the back of the watch.

They usually emit small, green LED lights onto your arm which can monitor capillary action, recording your pulse rate. Sophisticated devices detect changes in the bioimpedance that runs through the skin to get an idea of your nervous system activity.

Expert Perspectives

One expert says that overall for smartwatches, it's a "fine balance" - while the ever-evolving tech could realistically aid early diagnosis, "identifying issues before we feel unwell", it could also turn us the tracked into the "worried well".

He points out that some of the latest wearables can conduct tests like heart rhythm analysis, which regularly monitor how normal the heart is. They can alert if someone is experiencing atrial fibrillation (AF), where there is erratic electrical activity in the heart causing an uneven pulse.

This does not necessarily indicate someone is on the verge of a cardiac event, but it can give an preliminary indication they might be more susceptible of a blood clot in the long term.

But how to make sense of these figures is not straightforward. The expert worries that as additional features are incorporated, people may not be able to fully contextualise their data.

"I'm not entirely convinced that the ability to monitor so many metrics is such a good idea," he says.

A clinical psychologist studying wearable tech agrees. Her work into the influence of wearable tech on a set of individuals with health issues suggested a minority of those who were given devices to monitor their cardiac function experienced increased anxiety and were "far more likely to use healthcare resources".

She observed a cycle with her patients - they saw a alarming metric on their watch. They became worried. Their pulse went up. They got increasingly anxious. They looked a second time, and their reading increased again.

"Upon viewing numbers about ourselves that we lack context for then, of course, we are going to become concerned," the psychologist says. "We monitor, we check again - it becomes a self-fulfilling prophecy."