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There's a building tension. I can see the chilled vapour exhaled by my competitors as they execute the "about to run" jiggle on the beginning point.

A rapid movement of the hips.

I'm lined up for my local 5km community parkrun and I mean business. It's almost time...

Wait a second. I need to adjust my tracker. As does the runner next to me.

The person waiting sighs. I refuse to go until… there! GPS ready, I'm off.

Amidst the crowd, it's difficult to find a person without a wearable on it. And this extends beyond us participants who use them.

It's a thriving, multi-billion dollar sector. Companies like Samsung Galaxy dominate, all offering an extensive array of different devices to cater to a variety of lifestyles. Based on how advanced the watch you select, costs can range from a hundred pounds to a small fortune.

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

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

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

A handful of the reactions I've received from fellow smartwatch wearers when I ask what they think of theirs.

The Monitoring Conundrum

My thoughts on my own device? Currently, annoying. It's reporting I'm not hitting my target, making me wonder whether the foliage I'm running below are disrupting my GPS connection.

Millions of us fasten these compact gadgets onto our arms and wear them all day and night, apparently unconcerned with the fact they're constantly recording us.

A distant memory are the days when we depended on them exclusively to give us an estimation of our step count. Today, they can analyse our nightly rest, blood pressure, oxygen saturation, our body battery.

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

But can they do what they advertise? And are the statistics we scrutinise a accurate representation of reality? Do they enhance our overall health, or do the plethora of measurements and motivational messages just add to our everyday anxiety?

A Love-Hate Relationship

"I do get a bit preoccupied with mine," a wearer reveals.

While she loves how her device tracks her workouts, she finds some of its other capabilities "excessive" at times - a feeling first discovered during a major life event.

Until she found out she could put it into a specific mode, her smartwatch constantly alerted her she was being insufficiently energetic enough. In a new phase, the watch insists her she's had a bad night's sleep.

"I have a young baby, it's unnecessary for me to be told my sleep was poor," she says. "I'm acutely aware perfectly well."

Couldn't she just take it off?

"It's possible, I suppose, but I've got this love-hate relationship with it," she says. "I appreciate it for its workout tracking, I just wonder whether the myriad other functions it can now do is perhaps overkill for me."

How Do They Work?

Every device of smartwatch has its own novel way of measuring your bodily functions and analysing your data, but the majority use optical sensors on the underside of the watch.

They commonly shine small, green LED lights onto your arm which can detect pulsation, recording your heartbeat. More advanced devices analyse changes in the electrical current that runs through the skin to assess your stress levels.

A Fine Balance

A data scientist says that in general for smartwatches, it's a "difficult line" - while the rapidly advancing tech could realistically aid early diagnosis, "detecting disease before we notice anything", it could also turn us device users into the "anxious healthy".

He points out that newer wearables can carry out tests like medical-grade monitoring, which regularly monitor how healthy the heart is. They can notify if someone is experiencing atrial fibrillation (AF), where there is abnormal electrical activity in the heart causing an irregular heartbeat.

This does not mean someone is imminently going to suffer a cardiac event, but it can give an advance notice they might be more at risk of a blood clot in the future.

But how to make sense of these numbers is not straightforward. The expert worries that as additional features are introduced, people may find it hard to fully understand their data.

"I have some doubts that having the capacity to monitor so many metrics is such a positive development," he says.

A professor focusing on patient behaviour concurs. Research into the effect of wearable tech on a set of heart condition patients suggested a minority of those who were given devices to monitor their heart health experienced heightened worry and were "far more likely to use doctor's time".

She observed a vicious circle with her patients - they spotted a alarming metric on their watch. They felt anxious. Their heart rate went up. They got even more concerned. They checked again, and their reading rose further.

"Upon viewing stats about ourselves that we can't properly interpret then, understandably, we are going to become concerned," the psychologist says. "We monitor, we obsess - it becomes a vicious cycle."