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An atmosphere of feeling of anticipation. Visible is the cold breath exhaled by my competitors as they do the "pre-race" shuffle on the starting line.

A swift twitch of the hips.

I'm lined up for my local weekly parkrun event and I'm serious. The countdown begins...

Hold on. I must start my watch. The same goes for the runner beside me.

The person in the line sighs. I won't start until… yes! GPS ready, away I go.

Amidst the crowd, it's difficult to find a arm without a fitness tracker on it. And this extends beyond us runners who wear them.

This is a thriving, massive sector. Companies like Apple Watch lead the market, each with an broad selection of diverse devices to cater to a variety of lifestyles. According to how advanced the watch you go for, costs can start from £100 to a small fortune.

"I find it infuriating, I can't relax."

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

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

Just some of the responses I've received from fellow device users when I ask what they think of theirs.

The Monitoring Conundrum

My current opinion on mine? At this moment, annoying. It's telling me I'm not hitting my target, leading me to doubt whether the foliage along my route are interfering with my satellite signal.

Countless individuals of us strap these small gadgets onto our wrists and use them 24/7, ostensibly unconcerned with the fact they're constantly tracking us.

Long past are the days when we used them exclusively to give us an estimation of our daily steps. Now, they can measure our sleep quality, stress levels, heart rate variability (HRV), our recovery score.

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

But do they do what they say they do? And are the numbers we obsess over a faithful picture of the truth? Do they boost our mental and physical wellbeing, or do the multitude of measurements and cheerleading alerts just increase our daily stresses?

A Love-Hate Relationship

"I become a a little preoccupied with mine," a wearer reveals.

While she appreciates how her device tracks her workouts, she finds some of its other functions "overwhelming" at times - a feeling initially realised during a pregnancy.

Prior to discovering she could adjust the settings, her smartwatch constantly alerted her she was failing to be energetic enough. In a new phase, the watch frequently reports her she's had a restless night.

"I have a infant, I don't need to be notified my sleep was poor," she says. "I know that all too clearly."

Is it not possible to just remove it?

"I suppose I could, I suppose, but I've got this push-pull dynamic with it," she explains. "I value it for its workout tracking, I just wonder whether the additional features it can now do is maybe excessive for me."

The Technology Behind the Tracking

Every device of smartwatch has its own novel way of measuring your vitals and processing your data, but the vast bulk use optical sensors on the back of the watch.

They typically emit minute LED lights onto your wrist which can detect capillary action, identifying your pulse rate. More advanced devices measure changes in the bioimpedance that runs through the skin to gauge your nervous system activity.

A Fine Balance

A professor says that for most people for smartwatches, it's a "delicate equilibrium" - while the ever-evolving tech could realistically save lives, "identifying issues before we feel unwell", it could also turn us the tracked into the "concerned but fine".

He points out that newer wearables can carry out tests like heart rhythm analysis, which regularly monitor how normal the heart is. They can flag if someone is experiencing a heart arrhythmia, where there is erratic signals in the heart causing an arrhythmia.

This does not automatically signal someone is imminently going to suffer a heart attack, but it can give an preliminary indication they might be more susceptible of a heart problem in the years to come.

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

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

A health researcher studying patient behaviour concurs. Her work into the effect of wearable tech on a cohort of individuals with health issues suggested a minority of those who were given devices to monitor their cardiac function experienced greater stress and were "had a higher tendency to use healthcare resources".

She observed a cycle with her patients - they spotted a concerning reading on their watch. They grew concerned. Their heart rate went up. They got more worried. They re-examined the data, and their heart rate increased again.

"Upon viewing data about ourselves that we don't really understand then, naturally, we are going to want to know more," the psychologist says. "We look, we obsess - it becomes a feedback loop."