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There's a building tension. Apparent is the cold breath emanating from my rivals as they do the "starting line" shuffle on the start line.

A rapid twitch of the hips.

I'm at my local 5km community parkrun and I'm focused. It's almost time...

Wait a second. I need to adjust my watch. As does the guy alongside me.

The person in the line expresses impatience. I won't start until… done! Signal acquired, and I'm running.

In the mele, it's difficult to find a arm without a smartwatch on it. And this isn't only us runners who wear them.

This is a explosive, multi-billion dollar market. Brands like Apple Watch are prevalent, all offering an extensive range of different devices to cater to a range of budgets. Based on how high tech the device you select, prices can start from a hundred pounds to a small fortune.

"I find it infuriating, I can't switch off."

"It reassures me… It acts as a companion guiding me."

"Please don't notify me about a bad night's sleep."

A handful of the reactions I've received from fellow device users when I inquire what they their opinion is on theirs.

The Data Dilemma

My feelings on mine? Currently, annoying. It's indicating I'm off pace, causing me to question whether the trees I'm passing under are interfering with my GPS connection.

Millions of us attach these small devices onto our wrists and wear them all day and night, seemingly unconcerned with the fact they're continuously tracking us.

Long past are the days when we relied on them solely to give us an idea of our daily steps. Today, they can track our sleep quality, blood pressure, oxygen saturation, our body battery.

It's a challenge to find a physical metric they fail to monitor.

But are they able to do what they claim to do? And are the statistics we analyse a faithful picture of our actual health? Do they boost our daily wellness, or do the multitude of measurements and constant notifications just contribute to our everyday anxiety?

A Love-Hate Relationship

"I become a quite fixated with mine," one user admits.

While she values how her device records her runs, she finds some of its other features "daunting" at times - a feeling initially realised during a major life event.

Prior to discovering she could put it into a specific mode, her smartwatch constantly alerted her she was failing to be productive enough. Now, the watch keeps telling her she's had a bad night's sleep.

"I have a young baby, I don't need to be informed I'm tired," she says. "I know that only too well."

Why doesn't she just take it off?

"I could, theoretically, but I'm in this love-hate relationship with it," she continues. "I value it for its workout tracking, but I'm unsure whether the myriad other functions it can now do is possibly excessive for me."

How Do They Work?

Different brands of smartwatch has its own proprietary way of tracking your vitals and interpreting your data, but the vast bulk use detectors on the underside of the watch.

They usually project small, green LED lights onto your wrist which can detect blood flow, identifying your BPM. More advanced devices detect changes in the electrical current that flows through the skin to gauge your nervous system activity.

The Professional Viewpoint

One expert says that for most people for smartwatches, it's a "difficult line" - while the continuously improving tech could realistically prevent illness, "spotting abnormalities before we show symptoms", it could also turn us the tracked into the "concerned but fine".

He points out that newer wearables can perform tests like heart rhythm analysis, which constantly monitor how stable the heart is. They can notify if someone is experiencing atrial fibrillation (AF), where there is abnormal electrical activity in the heart causing an uneven pulse.

This does not necessarily indicate someone is about to have a cardiac event, but it can give an preliminary indication they might be more susceptible of a stroke in the years to come.

But how to understand these readings is complicated. The expert worries that as more functions are incorporated, people may not be able to fully comprehend their data.

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

A clinical psychologist focusing on wearable tech echoes this sentiment. A study into the influence of wearable tech on a set of cardiovascular patients suggested a noticeable percentage of those who were given devices to monitor their heart health experienced greater stress and were "more inclined to use doctor's time".

She observed a pattern with her patients - they saw a worrying figure on their watch. They felt anxious. Their heart rate went up. They got more worried. They looked a second time, and their anxiety rose further.

"Upon viewing data about ourselves that we can't properly interpret then, of course, we are going to want to know more," the psychologist says. "We monitor, we obsess - it becomes a feedback loop."