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An atmosphere of nervous excitement. I can see the chilled vapour exhaled by my fellow runners as they execute the "about to run" jiggle on the start line.

A rapid flick of the hips.

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

Oh, hang on. I must start my tracker. As does the runner next to me.

The person in the line tuts. I won't start until… there! Connection established, away I go.

Amidst the crowd, it's difficult to see a person without a fitness tracker on it. And it's not just us participants who wear them.

This is a booming, multi-billion dollar market. Companies like Apple Watch lead the market, all offering an broad array of diverse versions to suit a spectrum of budgets. Based on how high tech the model you select, price tags can vary between £100 to a significant investment.

"It drives me insane, I can't relax."

"It reassures me… It acts as a supporter encouraging me."

"Stop telling me I've experienced a bad night's sleep."

A small sample of the reactions I've received from other device users when I inquire what they their opinion is on theirs.

A Sea of Statistics

My thoughts on mine? At this moment, irritating. It's telling me I'm not hitting my target, making me wonder whether the trees I'm passing under are blocking my GPS connection.

A vast number of us fasten these compact devices onto our arms and wear them 24/7, ostensibly at ease with the fact they're perpetually monitoring us.

A distant memory are the days when we used them only to give us an rough count of our step count. Now, they can measure our nightly rest, stress levels, glucose levels, our VO2 max.

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 numbers we analyse a accurate representation of the truth? Do they enhance our overall health, or do the plethora of measurements and constant notifications just contribute to our everyday anxiety?

Addiction or Aid?

"I find myself getting a a little obsessed with mine," one user reveals.

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

Before she realised she could change its configuration, her smartwatch constantly alerted her she was not being active enough. In a new phase, the watch insists her she's had a bad night's sleep.

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

Is it not possible to just remove it?

"I could, I suppose, but I've got this love-hate relationship with it," she continues. "I value it for its exercise data, I just wonder whether the additional features it can now do is perhaps excessive for me."

Inside the Device

Every device of smartwatch has its own proprietary way of measuring your bodily functions and analysing your data, but the most use sensors on the back of the watch.

They typically emit minute LED lights onto your arm which can monitor capillary action, detecting your heartbeat. Higher-end devices measure changes in the electrical current that runs through the skin to gauge your nervous system activity.

The Professional Viewpoint

A data scientist says that for most people for smartwatches, it's a "difficult line" - while the rapidly advancing tech could actually aid early diagnosis, "spotting abnormalities before we notice anything", it could also turn us device users into the "worried well".

He points out that newer wearables can carry out tests like heart rhythm analysis, which continuously monitor how healthy the heart is. They can flag if someone is experiencing atrial fibrillation (AF), where there is erratic electrical activity in the heart causing an uneven pulse.

This does not necessarily indicate someone is imminently going to suffer a heart attack, but it can give an preliminary indication they might be more at risk of a stroke in the long term.

But how to make sense of these figures is not straightforward. The expert worries that as further capabilities are introduced, people may find it hard to fully comprehend their data.

"I have some doubts that having the capacity to monitor so much data is such a beneficial thing," he says.

A clinical psychologist studying cardiology concurs. Her work into the influence of wearable tech on a specific group of heart condition patients suggested a noticeable percentage of those who were given devices to monitor their heart health experienced increased anxiety and were "more inclined to use healthcare resources".

She identified a cycle with her patients - they saw a alarming metric on their watch. They became worried. Their BPM increased. They got increasingly anxious. They looked a second time, and their anxiety rose further.

"When people are presented with numbers about ourselves that we don't really understand then, naturally, we are going to become concerned," the psychologist says. "We monitor, we re-check - it becomes a vicious cycle."