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There's a nervous excitement. Visible is the chilled vapour emanating from my competitors as they perform the "about to run" wiggle on the starting line.

A swift flick of the hips.

I'm participating in my local Saturday morning race and I'm serious. Three, two, one...

Wait a second. I must adjust my device. So does the runner next to me.

The person behind us expresses impatience. I'm not moving until… there! GPS ready, I'm off.

Amidst the crowd, it's difficult to find a wrist without a fitness tracker on it. And this extends beyond us participants who use them.

We're witnessing a booming, multi-billion pound sector. Companies like Garmin dominate, all offering an broad selection of various devices to suit a spectrum of budgets. Based on how feature-packed the model you select, prices can vary between £100 to a significant investment.

"It drives me insane, it's impossible to stop checking."

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

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

Just some of the comments people have shared from other tracker enthusiasts when I inquire what they their opinion is on theirs.

The Monitoring Conundrum

My thoughts on mine? At this moment, irritating. It's indicating I'm not hitting my target, leading me to doubt whether the foliage along my route are interfering with my GPS connection.

A vast number of us fasten these small devices onto our arms and keep them on all day and night, ostensibly unconcerned with the fact they're continuously tracking us.

A distant memory are the days when we used them exclusively to give us an estimation of our step count. Today, they can analyse our sleep quality, blood pressure, glucose levels, our VO2 max.

It's tricky to find a health indicator they don't track.

But are they able to do what they claim to do? And are the numbers we scrutinise a accurate representation of our actual health? Do they boost our mental and physical wellbeing, or do the plethora of metrics and motivational messages just add to our daily stresses?

Addiction or Aid?

"I become a a little fixated with mine," one user confesses.

While she appreciates how her device monitors her exercise, she finds some of its other features "excessive" at times - a feeling initially realised during a significant period.

Before she realised she could change its configuration, her smartwatch repeatedly informed her she was being insufficiently productive enough. Now, the watch keeps telling her she's had a poor sleep score.

"I've got a six-month old, there's no point to be notified I'm tired," she says. "I know that only too well."

Couldn't she just take it off?

"It's possible, perhaps, but I've got this push-pull dynamic with it," she continues. "I appreciate it for its exercise data, but I'm unsure whether all the other things it can now do is possibly too much for me."

The Technology Behind the Tracking

Each model of smartwatch has its own novel way of tracking your health metrics and interpreting your data, but the vast bulk use detectors on the underside of the watch.

They usually project minute LED lights onto your arm which can monitor blood flow, identifying your BPM. Higher-end devices detect changes in the bioimpedance that runs through the skin to gauge your recovery state.

A Fine Balance

A professor says that in general for smartwatches, it's a "fine balance" - while the continuously improving tech could realistically save lives, "spotting abnormalities before we show symptoms", it could also turn us watch wearers into the "concerned but fine".

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

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

But how to understand these readings is complicated. The expert concerns that as further capabilities are incorporated, people may not be able to fully understand their data.

"I have some doubts that being able to monitor so many things is such a beneficial thing," he says.

A health researcher studying cardiology concurs. Her work into the impact of wearable tech on a cohort of cardiovascular patients suggested a minority of those who were given devices to monitor their cardiac function experienced heightened worry and were "far more likely to use medical services".

She observed a vicious circle with her patients - they noticed a alarming metric on their watch. They became worried. Their BPM went up. They got increasingly anxious. They re-examined the data, and their heart rate rose further.

"If we see stats 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."