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There's a building tension. Visible is the cold breath exhaled by my fellow runners as they do the "pre-race" jiggle on the start line.

A quick twitch of the hips.

I'm lined up for my local Saturday morning race and I'm focused. It's almost time...

Hold on. I need to sort my device. The same goes for the guy alongside me.

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

During the scramble, it's challenging to see a person without a wearable on it. And this extends beyond us participants who use them.

This is a booming, massive industry. Names like Samsung Galaxy are prevalent, featuring an broad range of various models to fit a variety of lifestyles. Depending on how feature-packed the device you go for, costs can range from £100 to a small fortune.

"It drives me insane, I'm unable to relax."

"It provides solace… It acts as a friend encouraging me."

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

A handful of the reactions I've received from fellow smartwatch wearers when I question what they feel about theirs.

The Data Dilemma

My feelings on mine? Currently, irritating. It's indicating I'm off pace, leading me to doubt whether the overhead branches I'm passing under are disrupting my GPS connection.

Millions of us attach these compact gadgets onto our wrists and use them 24/7, ostensibly unconcerned with the fact they're perpetually tracking us.

Long past are the days when we used them solely to give us an estimation of our pedometer reading. Today, they can track our nightly rest, stress levels, glucose levels, our VO2 max.

It's difficult to find a bodily function they aren't designed to measure.

But are they able to do what they say they do? And are the statistics we scrutinise a faithful picture of reality? Do they enhance our mental and physical wellbeing, or do the multitude of metrics and constant notifications just increase our everyday anxiety?

Addiction or Aid?

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

While she values how her device records her runs, she finds some of its other capabilities "overwhelming" at times - a feeling that became apparent during a significant period.

Until she found out she could put it into a specific mode, her smartwatch constantly alerted her she was failing to be active enough. Now, the watch insists her she's had a bad night's sleep.

"I have a six-month old, I don't need to be notified my sleep was poor," she says. "I'm acutely aware perfectly well."

Why doesn't she just remove it?

"I suppose I could, theoretically, but I've got this push-pull dynamic with it," she explains. "I value it for its fitness insights, I sometimes question whether all the other things it can now do is maybe overkill for me."

The Technology Behind the Tracking

Each model of smartwatch has its own unique way of tracking your health metrics and processing your data, but the majority use detectors on the reverse of the watch.

They usually shine small, green LED lights onto your arm which can detect capillary action, identifying your heartbeat. Higher-end devices measure changes in the skin conductance that passes over the skin to gauge your nervous system activity.

The Professional Viewpoint

A data scientist says that for most people for smartwatches, it's a "delicate equilibrium" - while the ever-evolving tech could realistically prevent illness, "spotting abnormalities before we notice anything", it could also turn us device users into the "anxious healthy".

He points out that the most advanced wearables can perform tests like medical-grade monitoring, which continuously monitor how normal the heart is. They can alert if someone is experiencing an irregular rhythm, where there is irregular signals in the heart causing an arrhythmia.

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

But how to understand these readings is not straightforward. The expert fears that as further capabilities are added, people may find it hard to fully understand their data.

"I have some doubts that being able to monitor so many things is such a beneficial thing," he says.

A health researcher specialising in cardiology agrees. Her work into the impact of wearable tech on a specific group of cardiovascular patients suggested a minority of those who were given devices to monitor their condition experienced increased anxiety and were "more inclined to use doctor's time".

She identified a vicious circle with her patients - they saw a concerning reading on their watch. They felt anxious. Their heart rate went up. They got even more concerned. They looked a second time, and their anxiety rose further.

"If we see numbers about ourselves that we can't properly interpret then, understandably, we are going to seek clarification," the psychologist says. "We look, we check again - it becomes a self-fulfilling prophecy."