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A sense of building tension. Apparent is the chilled vapour exhaled by my rivals as they perform the "starting line" jiggle on the start line.

A quick flick of the hips.

I'm participating in my local 5km community parkrun and I mean business. It's almost time...

Wait a second. I must sort my watch. As does the runner alongside me.

The person waiting tuts. I won't start until… done! Signal acquired, away I go.

Amidst the crowd, it's hard to see a arm without a fitness tracker on it. And it's not just us runners who wear them.

This is a thriving, multi-billion pound sector. Brands like Samsung Galaxy dominate, each with an broad range of diverse models to cater to a spectrum of budgets. Depending on how feature-packed the device you choose, price tags can range from an affordable sum to a small fortune.

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

"It comforts me… It acts as a friend guiding me."

"Stop telling me I've had a restless night."

A handful of the reactions I've had from other tracker enthusiasts when I inquire what they think of theirs.

A Sea of Statistics

My current opinion on mine? At this moment, frustrating. It's reporting I'm not hitting my target, leading me to doubt whether the foliage I'm passing under are disrupting my location tracking.

A vast number of us fasten these compact gadgets onto our wrists and keep them on all day and night, apparently unconcerned with the fact they're perpetually monitoring us.

Long past are the days when we used them solely to give us an rough count of our pedometer reading. Today, they can analyse our nightly rest, heart rate, oxygen saturation, our body battery.

It's tricky to find a physical metric they aren't designed to measure.

But do they do what they claim to do? And are the data points we scrutinise a faithful picture of the truth? Do they improve our mental and physical wellbeing, or do the multitude of metrics and motivational messages just contribute to our sense of overwhelm?

A Complicated Bond

"I find myself getting a bit preoccupied with mine," one user confesses.

While she values how her device records her exercise, she finds some of its other capabilities "daunting" at times - a feeling that became apparent during a significant period.

Prior to discovering she could change its configuration, her smartwatch kept telling her she was not being active enough. Now, the watch frequently reports her she's had a restless night.

"I've got a six-month old, it's unnecessary for me to be informed my sleep was poor," she says. "I know that perfectly well."

Couldn't she just remove it?

"I could, theoretically, but I have this love-hate relationship with it," she says. "I appreciate it for its fitness insights, but I'm unsure whether the myriad other functions it can now do is maybe too much for me."

How Do They Work?

Different brands of smartwatch has its own novel way of measuring your vitals and interpreting your data, but the most use optical sensors on the back of the watch.

They typically project tiny, coloured LED lights onto your wrist which can detect pulsation, detecting your pulse rate. More advanced devices detect changes in the skin conductance that flows through the skin to get an idea of your recovery state.

Expert Perspectives

A professor says that in general for smartwatches, it's a "fine balance" - while the rapidly advancing tech could realistically prevent illness, "detecting disease before we notice anything", it could also turn us the tracked into the "concerned but fine".

He points out that newer wearables can conduct tests like electrocardiograms (ECGs), which continuously monitor how stable the heart is. They can notify if someone is experiencing an irregular rhythm, where there is erratic impulses in the heart causing an uneven pulse.

This does not mean someone is on the verge of a heart attack, but it can give an advance notice they might be more susceptible of a stroke in the years to come.

But how to interpret these readings is complex. The expert concerns that as additional features are incorporated, people may struggle to fully understand their data.

"I remain sceptical that having the capacity to monitor so many metrics is such a beneficial thing," he says.

A clinical psychologist studying patient behaviour echoes this sentiment. Research into the impact of wearable tech on a cohort of heart condition patients suggested a significant portion of those who were given devices to monitor their condition experienced heightened worry 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 heart rate went up. They got more worried. They looked a second time, and their reading went up again.

"If we see data about ourselves that we don't really understand then, of course, we are going to become concerned," the psychologist says. "We check, we re-check - it becomes a vicious cycle."