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There's a building tension. Visible is the cold breath exhaled by my fellow runners as they execute the "about to run" shuffle on the start line.

A rapid movement of the hips.

I'm at my local Saturday morning race and I'm focused. It's almost time...

Hold on. I have to start my tracker. As does the guy alongside me.

The person behind us tuts. I won't start until… yes! GPS ready, away I go.

Amidst the crowd, it's hard to spot a arm without a smartwatch on it. And it's not just us athletes who rely on them.

It's a explosive, multi-billion pound industry. Brands like Samsung Galaxy are prevalent, featuring an extensive array of diverse models to suit a range of needs. According to how feature-packed the model you go for, costs can range from £100 to a small fortune.

"I find it infuriating, I'm unable to relax."

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

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

A handful of the reactions I've had from fellow device users when I question what they feel about theirs.

The Monitoring Conundrum

My feelings on mine? Currently, annoying. It's telling me I'm off pace, causing me to question whether the overhead branches I'm passing under are disrupting my satellite signal.

Countless individuals of us attach these little devices onto our wrists and wear them all day and night, seemingly 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. Currently, they can analyse our sleep patterns, stress levels, glucose levels, our VO2 max.

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

But are they able to do what they advertise? And are the statistics we scrutinise a accurate representation of the truth? Do they enhance our overall health, or do the avalanche of metrics and constant notifications just contribute to our everyday anxiety?

A Love-Hate Relationship

"I do get a quite fixated with mine," a wearer confesses.

While she values how her device records her exercise, she finds some of its other features "overwhelming" at times - a feeling initially realised 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. Later on, the watch insists her she's had a bad night's sleep.

"I have a six-month old, it's unnecessary for me to be told I've not slept," she says. "I know that only too well."

Is it not possible to just take it off?

"I suppose I could, theoretically, but I have this complicated dynamic with it," she continues. "I value it for its fitness insights, I just wonder whether the additional features it can now do is possibly too much for me."

How Do They Work?

Each model of smartwatch has its own proprietary way of tracking your health metrics and interpreting your data, but the most use detectors on the back of the watch.

They usually project small, green LED lights onto your arm which can detect capillary action, identifying your pulse rate. Sophisticated devices measure changes in the electrical current that flows through the skin to assess your nervous system activity.

Expert Perspectives

A professor says that in general for smartwatches, it's a "fine balance" - while the ever-evolving tech could actually aid early diagnosis, "detecting disease before we show symptoms", it could also turn us the tracked into the "concerned but fine".

He points out that newer wearables can carry out 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 irregular electrical activity in the heart causing an irregular heartbeat.

This does not mean someone is imminently going to suffer a cardiac event, but it can give an preliminary indication they might be more vulnerable of a heart problem in the years to come.

But how to interpret these readings is complicated. The expert concerns that as more functions are added, people may find it hard to fully comprehend their data.

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

A clinical psychologist studying wearable tech agrees. A study into the effect of wearable tech on a cohort of cardiovascular patients suggested a minority of those who were given devices to monitor their heart health experienced increased anxiety and were "more inclined to use healthcare resources".

She identified a pattern with her patients - they noticed a alarming metric on their watch. They grew concerned. Their heart rate rose. They got increasingly anxious. They looked a second time, and their heart rate went up again.

"If we see stats about ourselves that we lack context for then, naturally, we are going to become concerned," the psychologist says. "We monitor, we obsess - it becomes a self-fulfilling prophecy."