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A sense of building tension. Visible is the frosty air coming from my fellow runners as they perform the "starting line" wiggle on the starting line.

A quick flick of the hips.

I'm lined up for my local 5km community parkrun and I'm serious. Three, two, one...

Hold on. I have to start my watch. As does the runner beside me.

The person in the line sighs. I'm not moving until… yes! Connection established, away I go.

Amidst the crowd, it's difficult to find a wrist without a fitness tracker on it. And this isn't only us athletes who rely on them.

We're witnessing a thriving, massive industry. Brands like Garmin are prevalent, all offering an wide selection of diverse models to cater to a spectrum of lifestyles. Depending on how high tech the watch you select, prices can vary between £100 to thousands of pounds.

"It makes me crazy, I can't stop checking."

"It reassures me… It feels like a supporter encouraging me."

"I wish it wouldn't say I've experienced a poor sleep."

A handful of the comments people have shared from other tracker enthusiasts when I question what they think of theirs.

The Data Dilemma

My current opinion on mine? Right now, annoying. It's reporting I'm off pace, making me wonder whether the foliage I'm running below are interfering with my satellite signal.

Millions of us strap these little devices onto our wrists and use them all day and night, ostensibly at ease with the fact they're constantly recording us.

Gone are the days when we relied on them solely to give us an rough count of our daily steps. Currently, they can track our nightly rest, heart rate, glucose levels, our body battery.

It's tricky to find a health indicator they don't track.

But do they do what they say they do? And are the data points we obsess over a faithful picture of reality? Do they enhance our overall health, or do the avalanche of metrics and constant notifications just increase our everyday anxiety?

A Complicated Bond

"I do get a quite obsessed with mine," a wearer confesses.

While she values how her device monitors her workouts, she finds some of its other functions "daunting" at times - a feeling initially realised during a significant period.

Until she found out she could change its configuration, her smartwatch kept telling her she was not being productive enough. Later on, the watch frequently reports her she's had a poor sleep score.

"I have a six-month old, there's no point to be notified my sleep was poor," she says. "That fact is only too well."

Couldn't she just remove it?

"I suppose I could, perhaps, but I've got this love-hate relationship with it," she says. "I love it for its fitness insights, but I'm unsure whether the additional features it can now do is perhaps too much for me."

How Do They Work?

Each model of smartwatch has its own unique way of measuring your health metrics and processing your data, but the majority use sensors on the underside of the watch.

They typically project small, green LED lights onto your wrist which can observe capillary action, recording your pulse rate. Higher-end devices analyse changes in the bioimpedance that passes over the skin to gauge your nervous system activity.

Expert Perspectives

A data scientist says that for most people for smartwatches, it's a "delicate equilibrium" - while the rapidly advancing tech could realistically aid early diagnosis, "spotting abnormalities before we feel unwell", it could also turn us watch wearers into the "concerned but fine".

He points out that newer wearables can conduct tests like electrocardiograms (ECGs), which continuously monitor how healthy the heart is. They can flag if someone is experiencing a heart arrhythmia, where there is erratic electrical activity in the heart causing an uneven pulse.

This does not automatically signal someone is imminently going to suffer a heart attack, but it can give an early warning they might be more vulnerable of a heart problem in the years to come.

But how to make sense of these numbers is complex. The expert concerns that as additional features are incorporated, people may struggle to fully understand their data.

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

A clinical psychologist focusing on cardiology echoes this sentiment. A study into the influence of wearable tech on a cohort of individuals with health issues suggested a minority of those who were given devices to monitor their heart health experienced increased anxiety and were "had a higher tendency to use healthcare resources".

She identified a pattern with her patients - they noticed a concerning reading on their watch. They felt anxious. Their BPM increased. They got even more concerned. They re-examined the data, and their anxiety increased again.

"If we see stats about ourselves that we don't really understand then, of course, we are going to become concerned," the psychologist says. "We monitor, we obsess - it becomes a vicious cycle."