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There's a building tension. I can see the chilled vapour exhaled by my rivals as they do the "about to run" shuffle on the start line.

A swift twitch of the hips.

I'm participating in my local weekly parkrun event and I'm serious. Three, two, one...

Hold on. I must sort my device. The same goes for the runner beside me.

The person behind us tuts. I'm not moving until… yes! GPS ready, and I'm running.

In the mele, it's difficult to see a person without a fitness tracker on it. And this isn't only us runners who rely on them.

We're witnessing a thriving, multi-billion dollar market. Brands like Samsung Galaxy dominate, featuring an extensive selection of various devices to cater to a variety of budgets. Based on how feature-packed the device you select, costs can range from £100 to thousands of pounds.

"It drives me insane, it's impossible to switch off."

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

"I wish it wouldn't say about a bad night's sleep."

Just some of the comments I've had from other device users when I ask what they feel about theirs.

The Monitoring Conundrum

My feelings on my own device? Currently, frustrating. It's telling me my speed is wrong, causing me to question whether the overhead branches along my route are disrupting my satellite signal.

Countless individuals of us fasten these compact monitors onto our wrists and keep them on all day and night, ostensibly comfortable with the fact they're perpetually monitoring us.

Gone are the days when we used them only to give us an estimation of our pedometer reading. Today, they can measure our nightly rest, blood pressure, glucose levels, our body battery.

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

But can they do what they say they do? And are the statistics we scrutinise a accurate representation of our actual health? Do they enhance our mental and physical wellbeing, or do the avalanche of readings and cheerleading alerts just contribute to our everyday anxiety?

Addiction or Aid?

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

While she appreciates how her device records her exercise, she finds some of its other functions "daunting" at times - a feeling that became apparent during a major life event.

Prior to discovering she could change its configuration, her smartwatch constantly alerted her she was not being active enough. In a new phase, the watch keeps telling her she's had a restless night.

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

Why doesn't she just take it off?

"I suppose I could, I suppose, but I've got this complicated dynamic with it," she explains. "I value it for its workout tracking, I just wonder whether the myriad other functions it can now do is possibly excessive for me."

The Technology Behind the Tracking

Different brands of smartwatch has its own proprietary way of monitoring your bodily functions and processing your data, but the most use detectors on the reverse of the watch.

They typically emit minute LED lights onto your wrist which can detect pulsation, identifying your BPM. More advanced devices detect changes in the bioimpedance that flows through the skin to assess your stress levels.

The Professional Viewpoint

A professor says that in general for smartwatches, it's a "difficult line" - while the continuously improving tech could potentially prevent illness, "spotting abnormalities before we show symptoms", it could also turn us watch wearers into the "worried well".

He points out that newer wearables can conduct tests like medical-grade monitoring, which continuously monitor how stable the heart is. They can alert if someone is experiencing atrial fibrillation (AF), where there is abnormal signals in the heart causing an arrhythmia.

This does not necessarily indicate someone is about to have a heart attack, but it can give an advance notice they might be more vulnerable of a stroke in the future.

But how to understand these figures is complex. The expert worries that as further capabilities are added, people may not be able to fully comprehend their data.

"I'm not entirely convinced that being able to monitor so many metrics is such a beneficial thing," he says.

A health researcher studying cardiology echoes this sentiment. Research into the impact of wearable tech on a specific group of heart condition patients suggested a noticeable percentage of those who were given devices to monitor their condition experienced heightened worry and were "far more likely to use healthcare resources".

She noted a vicious circle with her patients - they noticed a concerning reading on their watch. They became worried. Their heart rate rose. They got increasingly anxious. They looked a second time, and their reading increased again.

"Upon viewing stats about ourselves that we don't really understand then, of course, we are going to become concerned," the psychologist says. "We monitor, we re-check - it becomes a feedback loop."