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There's a building tension. Visible is the chilled vapour exhaled by my rivals as they perform the "starting line" wiggle on the start line.

A quick twitch of the hips.

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

Oh, hang on. I must start my watch. As does the runner alongside me.

The person behind us tuts. I refuse to go until… yes! GPS ready, away I go.

During the scramble, it's challenging to spot a arm without a smartwatch on it. And this extends beyond us runners who use them.

It's a thriving, multi-billion dollar market. Names like Garmin are prevalent, each with an extensive range of various versions to cater to a spectrum of budgets. Depending on how high tech the watch you select, costs can range from a hundred pounds to a small fortune.

"I find it infuriating, I can't relax."

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

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

A small sample of the reactions I've received from other smartwatch wearers when I inquire what they think of theirs.

The Monitoring Conundrum

My thoughts on my own device? Right now, irritating. It's indicating I'm not hitting my target, causing me to question whether the overhead branches along my route are interfering with my location tracking.

A vast number of us fasten these compact gadgets onto our arms and keep them on constantly, seemingly comfortable with the fact they're constantly monitoring us.

Gone are the days when we used them solely to give us an rough count of our daily steps. Today, they can analyse our sleep patterns, blood pressure, oxygen saturation, our VO2 max.

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

But are they able to do what they say they do? And are the data points we analyse a faithful picture of reality? Do they improve our overall health, or do the plethora of metrics and motivational messages just add to our everyday anxiety?

A Love-Hate Relationship

"I find myself getting a bit obsessed with mine," one user admits.

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

Until she found out she could adjust the settings, her smartwatch kept telling her she was failing to be energetic enough. Later on, the watch frequently reports her she's had a restless night.

"I've got a six-month old, there's no point to be notified I've not slept," she says. "That fact is only too well."

Is it not possible to just remove it?

"It's possible, theoretically, but I've got this complicated dynamic with it," she continues. "I love it for its exercise data, I just wonder whether all the other things it can now do is possibly excessive for me."

How Do They Work?

Each model of smartwatch has its own novel way of tracking your vitals and interpreting your data, but the vast bulk use sensors on the reverse of the watch.

They typically emit tiny, coloured LED lights onto your wrist which can observe capillary action, identifying your heartbeat. Sophisticated devices detect changes in the bioimpedance that flows through the skin to get an idea of your nervous system activity.

A Fine Balance

One expert says that for most people for smartwatches, it's a "difficult line" - while the rapidly advancing tech could actually save lives, "detecting disease before we show symptoms", it could also turn us device users into the "anxious healthy".

He points out that some of the latest wearables can carry out tests like medical-grade monitoring, which continuously monitor how normal the heart is. They can flag if someone is experiencing a heart arrhythmia, where there is abnormal impulses in the heart causing an irregular heartbeat.

This does not necessarily indicate someone is on the verge of a heart attack, but it can give an advance notice they might be more vulnerable of a blood clot in the future.

But how to understand these figures is not straightforward. The expert concerns that as further capabilities are incorporated, people may not be able to fully contextualise their data.

"I'm not entirely convinced that the ability to monitor so much data is such a beneficial thing," he says.

A professor focusing on wearable tech concurs. Her work into the impact of wearable tech on a set of cardiovascular patients suggested a noticeable percentage of those who were given devices to monitor their condition experienced increased anxiety and were "more inclined to use medical services".

She identified a cycle with her patients - they saw a concerning reading on their watch. They grew concerned. Their pulse went up. They got even more concerned. They checked again, and their anxiety went up again.

"If we see numbers about ourselves that we lack context for then, understandably, we are going to become concerned," the psychologist says. "We check, we check again - it becomes a vicious cycle."