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A sense of building tension. I can see the cold breath exhaled by my rivals as they perform the "pre-race" jiggle on the starting line.

A rapid flick of the hips.

I'm participating in my local weekly parkrun event and I'm serious. The countdown begins...

Hold on. I need to adjust my device. As does the person beside me.

The person in the line expresses impatience. I'm not moving until… yes! Connection established, and I'm running.

During the scramble, it's difficult to see a arm without a fitness tracker on it. And this extends beyond us athletes who wear them.

It's a explosive, multi-billion pound sector. Companies like Apple Watch dominate, featuring an broad array of various devices to fit a spectrum of lifestyles. Depending on how feature-packed the device you go for, prices can start from an affordable sum to thousands of pounds.

"I find it infuriating, I'm unable to switch off."

"It comforts me… It's like a friend supporting me."

"I wish it wouldn't say I've had a bad night's sleep."

A small sample of the comments I've had from fellow device users when I inquire what they think of theirs.

The Monitoring Conundrum

My thoughts on mine? At this moment, irritating. It's indicating my speed is wrong, making me wonder whether the foliage along my route are interfering with my satellite signal.

A vast number of us strap these compact devices onto our arms and use 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 idea of our daily steps. Today, they can measure our nightly rest, stress levels, heart rate variability (HRV), our VO2 max.

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

But are they able to do what they say they do? And are the numbers we scrutinise a accurate representation of our actual health? Do they improve our mental and physical wellbeing, or do the avalanche of readings and constant notifications just increase our everyday anxiety?

A Love-Hate Relationship

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

While she appreciates how her device monitors her runs, she finds some of its other features "excessive" at times - a feeling that became apparent during a major life event.

Before she realised she could change its configuration, her smartwatch constantly alerted her she was failing to be active enough. In a new phase, the watch keeps telling her she's had a bad night's sleep.

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

Why doesn't she just stop wearing it?

"I could, perhaps, but I have this complicated dynamic with it," she continues. "I appreciate it for its workout tracking, but I'm unsure whether all the other things it can now do is maybe too much for me."

The Technology Behind the Tracking

Different brands of smartwatch has its own proprietary way of monitoring your vitals and analysing your data, but the majority use sensors on the underside of the watch.

They usually shine small, green LED lights onto your arm which can observe pulsation, detecting your heartbeat. Higher-end devices measure changes in the electrical current that passes over the skin to assess your stress levels.

The Professional Viewpoint

One expert says that in general for smartwatches, it's a "difficult line" - while the rapidly advancing tech could actually save lives, "identifying issues before we feel unwell", it could also turn us the tracked into the "worried well".

He points out that newer wearables can perform 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 abnormal signals in the heart causing an uneven pulse.

This does not mean someone is about to have a cardiac event, but it can give an preliminary indication they might be more vulnerable of a heart problem in the future.

But how to understand these figures is not straightforward. The expert concerns that as more functions are introduced, people may struggle to fully comprehend their data.

"I remain sceptical that having the capacity to monitor so much data is such a good idea," he says.

A professor specialising in wearable tech concurs. Research into the impact of wearable tech on a set of individuals with health issues suggested a significant portion of those who were given devices to monitor their heart health experienced greater stress and were "more inclined to use doctor's time".

She identified a cycle with her patients - they saw a concerning reading on their watch. They grew concerned. Their BPM rose. They got increasingly anxious. They checked again, and their heart rate rose further.

"When people are presented with data about ourselves that we lack context for then, naturally, we are going to become concerned," the psychologist says. "We look, we re-check - it becomes a feedback loop."