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There's a building tension. Visible is the chilled vapour exhaled by my fellow runners as they do the "about to run" jiggle on the start line.

A swift twitch of the hips.

I'm lined up for my local 5km community parkrun and I mean business. The countdown begins...

Oh, hang on. I have to start my tracker. As does the guy next to me.

The person waiting expresses impatience. I'm not moving until… done! Connection established, I'm off.

Amidst the crowd, it's difficult to spot a wrist without a smartwatch on it. And it's not just us athletes who wear them.

This is a explosive, multi-billion dollar industry. Names like Garmin lead the market, all offering an wide selection of diverse devices to suit a spectrum of lifestyles. Based on how feature-packed the device you choose, costs can vary between £100 to a small fortune.

"It makes me crazy, it's impossible to switch off."

"It comforts me… It acts as a friend guiding me."

"Stop telling me I've had a poor sleep."

Just some of the comments I've had from fellow tracker enthusiasts when I ask what they their opinion is on theirs.

The Monitoring Conundrum

My current opinion on mine? At this moment, irritating. It's reporting my speed is wrong, making me wonder whether the overhead branches I'm running below are disrupting my location tracking.

A vast number of us strap these small devices onto our wrists and wear them constantly, apparently comfortable with the fact they're perpetually monitoring us.

A distant memory are the days when we relied on them only to give us an idea of our step count. Now, they can measure our nightly rest, blood pressure, oxygen saturation, our VO2 max.

It's difficult to find a physical metric they don't track.

But are they able to do what they say they do? And are the statistics we scrutinise a accurate representation of reality? Do they improve our overall health, or do the avalanche of metrics and constant notifications just increase our everyday anxiety?

Addiction or Aid?

"I find myself getting a bit fixated with mine," an individual reveals.

While she loves how her device monitors her workouts, she finds some of its other capabilities "excessive" at times - a feeling that became apparent during a pregnancy.

Until she found out she could change its configuration, her smartwatch constantly alerted her she was failing to be energetic enough. Now, the watch insists her she's had a restless night.

"I have a six-month old, I don't need to be informed my sleep was poor," she says. "I'm acutely aware all too clearly."

Couldn't she just take it off?

"It's possible, theoretically, but I have this love-hate relationship with it," she continues. "I love it for its fitness insights, I sometimes question whether the myriad other functions it can now do is maybe overkill for me."

Inside the Device

Every device of smartwatch has its own novel way of measuring your health metrics and interpreting your data, but the vast bulk use optical sensors on the reverse of the watch.

They typically emit minute LED lights onto your wrist which can observe capillary action, identifying your BPM. Higher-end devices analyse changes in the bioimpedance that passes over the skin to gauge your nervous system activity.

Expert Perspectives

A professor says that in general for smartwatches, it's a "fine balance" - while the rapidly advancing tech could realistically prevent illness, "identifying issues before we feel unwell", it could also turn us the tracked into the "anxious healthy".

He points out that newer wearables can conduct tests like electrocardiograms (ECGs), which regularly monitor how normal the heart is. They can flag if someone is experiencing a heart arrhythmia, where there is erratic impulses in the heart causing an irregular heartbeat.

This does not necessarily indicate someone is about to have a cardiac event, but it can give an advance notice they might be more vulnerable of a heart problem in the long term.

But how to make sense of these numbers is complex. The expert concerns that as more functions are added, people may find it hard to fully comprehend their data.

"I remain sceptical that having the capacity to monitor so much data is such a good idea," he says.

A health researcher focusing on patient behaviour concurs. A study into the influence of wearable tech on a specific group of individuals with health issues suggested a significant portion of those who were given devices to monitor their heart health experienced greater stress and were "far more likely to use doctor's time".

She observed a vicious circle with her patients - they noticed a worrying figure on their watch. They felt anxious. Their pulse rose. They got even more concerned. They checked again, and their reading increased again.

"If we see numbers about ourselves that we don't really understand then, of course, we are going to want to know more," the psychologist says. "We check, we check again - it becomes a vicious cycle."