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A sense of building tension. Visible is the frosty air coming from my rivals as they execute the "pre-race" wiggle on the beginning point.

A swift flick of the hips.

I'm lined up for my local 5km community parkrun and I'm serious. Three, two, one...

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

The person waiting expresses impatience. I won't start until… there! Connection established, and I'm running.

Amidst the crowd, it's hard to see a wrist without a fitness tracker on it. And this extends beyond us athletes who wear them.

It's a booming, multi-billion pound industry. Companies like Garmin lead the market, each with an broad selection of different versions to suit a range of lifestyles. Depending on how high tech the model you select, price tags can start from an affordable sum to a small fortune.

"It makes me crazy, I can't relax."

"It comforts me… It feels like a friend encouraging me."

"Please don't notify me I've experienced a poor sleep."

A small sample of the reactions I've had from fellow tracker enthusiasts when I question what they think of theirs.

The Monitoring Conundrum

My current opinion on mine? Currently, annoying. It's telling me my speed is wrong, leading me to doubt whether the overhead branches I'm running below are interfering with my GPS connection.

Millions of us attach these small monitors onto our arms and wear them all day and night, ostensibly comfortable with the fact they're continuously monitoring us.

Long past are the days when we relied on them solely to give us an rough count of our pedometer reading. Now, they can measure our sleep patterns, heart rate, oxygen saturation, our recovery score.

It's a challenge to find a health indicator they fail to monitor.

But are they able to do what they say they do? And are the numbers we scrutinise a accurate representation of reality? Do they boost our daily wellness, or do the multitude of readings and motivational messages just add to our daily stresses?

A Complicated Bond

"I do get a bit preoccupied with mine," one user reveals.

While she loves how her device tracks her workouts, she finds some of its other capabilities "daunting" at times - a feeling first discovered during a pregnancy.

Before she realised she could put it into a specific mode, her smartwatch constantly alerted her she was being insufficiently active enough. In a new phase, the watch frequently reports her she's had a bad night's sleep.

"I've got a infant, I don't need to be notified my sleep was poor," she says. "I'm acutely aware perfectly well."

Couldn't she just take it off?

"I could, I suppose, but I have this love-hate relationship with it," she explains. "I value it for its workout tracking, I just wonder whether the myriad other functions it can now do is maybe too much for me."

How Do They Work?

Every device of smartwatch has its own proprietary way of monitoring your vitals and analysing your data, but the most use detectors on the underside of the watch.

They commonly project small, green LED lights onto your wrist which can detect capillary action, detecting your heartbeat. More advanced devices measure changes in the bioimpedance that passes over the skin to assess your nervous system activity.

A Fine Balance

One expert says that in general for smartwatches, it's a "fine balance" - while the rapidly advancing tech could actually save lives, "detecting disease before we feel unwell", it could also turn us watch wearers into the "worried well".

He points out that the most advanced wearables can perform tests like heart rhythm analysis, which regularly monitor how stable the heart is. They can alert if someone is experiencing a heart arrhythmia, where there is irregular impulses in the heart causing an irregular heartbeat.

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 heart problem in the future.

But how to make sense of these readings is complicated. The expert concerns that as further capabilities are introduced, people may find it hard to fully comprehend their data.

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

A professor studying patient behaviour concurs. Her work into the impact of wearable tech on a specific group of heart condition patients suggested a minority of those who were given devices to monitor their heart health experienced heightened worry and were "had a higher tendency to use healthcare resources".

She observed a pattern with her patients - they spotted a concerning reading on their watch. They felt anxious. Their pulse went up. They got even more concerned. They re-examined the data, and their anxiety increased again.

"Upon viewing data about ourselves that we can't properly interpret then, understandably, we are going to want to know more," the psychologist says. "We check, we obsess - it becomes a self-fulfilling prophecy."