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A sense of nervous excitement. Visible is the chilled vapour coming from my competitors as they perform the "pre-race" wiggle on the starting line.

A rapid movement of the hips.

I'm lined up for my local weekly parkrun event and I'm focused. Three, two, one...

Hold on. I have to sort my watch. So does the guy alongside me.

The person waiting expresses impatience. I won't start until… done! GPS ready, away I go.

In the mele, it's challenging to spot a wrist without a fitness tracker on it. And it's not just us participants who wear them.

It's a booming, multi-billion pound sector. Companies like Apple Watch dominate, featuring an broad array of different devices to fit a variety of needs. According to how advanced the device you choose, price tags can start from £100 to a significant investment.

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

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

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

A small sample of the responses I've had from fellow tracker enthusiasts when I question what they their opinion is on theirs.

The Monitoring Conundrum

My feelings on my own device? At this moment, annoying. It's indicating my speed is wrong, leading me to doubt whether the overhead branches I'm passing under are disrupting my satellite signal.

Millions of us strap these small devices onto our wrists and keep them on 24/7, ostensibly at ease with the fact they're perpetually tracking us.

Gone are the days when we relied on them solely to give us an idea of our daily steps. Currently, they can track our sleep patterns, heart rate, oxygen saturation, our VO2 max.

It's tricky to find a health indicator they aren't designed to measure.

But are they able to do what they advertise? And are the numbers we scrutinise a accurate representation of the truth? Do they improve our daily wellness, or do the multitude of metrics and constant notifications just increase our everyday anxiety?

A Complicated Bond

"I become a a little preoccupied with mine," a wearer confesses.

While she appreciates how her device tracks her runs, she finds some of its other capabilities "overwhelming" at times - a feeling first discovered during a significant period.

Before she realised she could change its configuration, her smartwatch constantly alerted her she was failing to be energetic enough. Now, the watch insists her she's had a poor sleep score.

"I have a six-month old, it's unnecessary for me to be told I've not slept," she says. "That fact is only too well."

Is it not possible to just stop wearing it?

"I could, perhaps, but I have this complicated dynamic with it," she explains. "I love it for its workout tracking, but I'm unsure whether the additional features it can now do is possibly overkill for me."

The Technology Behind the Tracking

Each model of smartwatch has its own proprietary way of tracking your bodily functions and interpreting your data, but the vast bulk use sensors on the underside of the watch.

They usually project minute LED lights onto your wrist which can observe blood flow, detecting your heartbeat. More advanced devices measure changes in the bioimpedance that runs through the skin to gauge your nervous system activity.

A Fine Balance

One expert says that overall for smartwatches, it's a "delicate equilibrium" - while the continuously improving tech could potentially aid early diagnosis, "identifying issues before we show symptoms", it could also turn us device users into the "concerned but fine".

He points out that the most advanced wearables can perform tests like heart rhythm analysis, which regularly monitor how normal the heart is. They can flag if someone is experiencing an irregular rhythm, where there is erratic impulses in the heart causing an uneven pulse.

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

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

"I have some doubts that being able to monitor so much data is such a positive development," he says.

A clinical psychologist studying wearable tech echoes this sentiment. A study into the influence of wearable tech on a cohort of cardiovascular patients suggested a minority of those who were given devices to monitor their heart health experienced greater stress and were "more inclined to use medical services".

She identified a cycle with her patients - they saw a concerning reading on their watch. They became worried. Their pulse rose. They got even more concerned. They re-examined the data, and their reading rose further.

"If we see numbers about ourselves that we lack context for then, naturally, we are going to want to know more," the psychologist says. "We check, we re-check - it becomes a self-fulfilling prophecy."