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A sense of feeling of anticipation. I can see the cold breath exhaled by my competitors as they execute the "about to run" jiggle on the starting line.

A quick flick of the hips.

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

Wait a second. I have to sort my tracker. The same goes for the runner alongside me.

The person in the line tuts. I'm not moving until… done! Signal acquired, away I go.

In the mele, it's challenging to spot a arm without a fitness tracker on it. And this extends beyond us participants who use them.

It's a booming, multi-billion pound market. Names like Samsung Galaxy are prevalent, each with an extensive selection of diverse devices to suit a range of lifestyles. According to how high tech the watch you go for, price tags can range from £100 to thousands of pounds.

"It makes me crazy, I'm unable to relax."

"It reassures me… It feels like a supporter supporting me."

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

A small sample of the reactions I've had from fellow smartwatch wearers when I ask what they think of theirs.

The Data Dilemma

My current opinion on my own device? Right now, annoying. It's telling me I'm off pace, leading me to doubt whether the trees I'm running below are interfering with my satellite signal.

A vast number of us strap these little devices onto our arms and keep them on all day and night, apparently at ease with the fact they're continuously monitoring us.

A distant memory are the days when we relied on them solely to give us an rough count of our step count. Currently, they can measure our sleep quality, blood pressure, heart rate variability (HRV), our VO2 max.

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

But do they do what they say they do? And are the statistics we scrutinise a faithful picture of the truth? Do they improve our overall health, or do the multitude of measurements and motivational messages just add to our daily stresses?

A Complicated Bond

"I become a a little obsessed with mine," a wearer admits.

While she loves how her device tracks her workouts, she finds some of its other functions "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. Now, the watch keeps telling her she's had a bad night's sleep.

"I've got a young baby, it's unnecessary for me to be told I'm tired," she says. "I know that all too clearly."

Why doesn't she just remove it?

"I could, perhaps, but I've got this complicated dynamic with it," she continues. "I love it for its exercise data, but I'm unsure whether all the other things it can now do is possibly overkill for me."

How Do They Work?

Every device of smartwatch has its own novel way of monitoring your bodily functions and processing your data, but the most use detectors on the back of the watch.

They usually project small, green LED lights onto your wrist which can monitor blood flow, recording your pulse rate. Higher-end devices detect changes in the bioimpedance that runs through the skin to assess your recovery state.

Expert Perspectives

A professor says that in general for smartwatches, it's a "difficult line" - while the ever-evolving tech could realistically save lives, "spotting abnormalities before we feel unwell", it could also turn us device users into the "worried well".

He points out that the most advanced wearables can perform tests like electrocardiograms (ECGs), which constantly monitor how normal the heart is. They can flag if someone is experiencing a heart arrhythmia, where there is abnormal electrical activity in the heart causing an irregular heartbeat.

This does not automatically signal someone is on the verge of a cardiac event, but it can give an advance notice they might be more susceptible of a blood clot in the future.

But how to understand these readings is complex. The expert worries that as further capabilities are incorporated, people may find it hard to fully understand their data.

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

A clinical psychologist focusing on wearable tech echoes this sentiment. A study into the influence of wearable tech on a specific group of individuals with health issues suggested a minority of those who were given devices to monitor their cardiac function experienced increased anxiety and were "far more likely to use medical services".

She noted a pattern with her patients - they spotted a alarming metric on their watch. They became worried. Their heart rate increased. They got even more concerned. They looked a second time, and their reading increased again.

"If we see data about ourselves that we lack context for then, of course, we are going to seek clarification," the psychologist says. "We look, we obsess - it becomes a vicious cycle."