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A sense of building tension. Apparent is the chilled vapour exhaled by my rivals as they do the "pre-race" wiggle on the start line.

A quick movement of the hips.

I'm at my local weekly parkrun event and I'm serious. Three, two, one...

Wait a second. I have to start my device. So does the person alongside me.

The person in the line tuts. I won't start until… there! Connection established, away I go.

In the mele, it's difficult to see a person without a smartwatch on it. And this isn't only us participants who use them.

It's a explosive, multi-billion dollar market. Brands like Apple Watch dominate, featuring an wide range of various devices to cater to a variety of lifestyles. According to how advanced the watch you go for, costs can range from £100 to a small fortune.

"It drives me insane, I'm unable to relax."

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

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

Just some of the reactions I've had from other tracker enthusiasts when I inquire what they think of theirs.

A Sea of Statistics

My feelings on my own device? At this moment, annoying. It's reporting I'm off pace, leading me to doubt whether the foliage I'm running below are disrupting my GPS connection.

Countless individuals of us fasten these small gadgets onto our arms and keep them on all day and night, ostensibly comfortable with the fact they're constantly tracking us.

A distant memory are the days when we used them solely to give us an estimation of our pedometer reading. Today, they can track our nightly rest, heart rate, glucose levels, our VO2 max.

It's a challenge to find a health indicator they aren't designed to measure.

But are they able to do what they claim to do? And are the data points we scrutinise a true reflection of our actual health? Do they improve our overall health, or do the avalanche of measurements and motivational messages just add to our everyday anxiety?

A Love-Hate Relationship

"I become a bit preoccupied with mine," a wearer admits.

While she loves how her device tracks her exercise, she finds some of its other functions "excessive" at times - a feeling first discovered during a major life event.

Until she found out she could change its configuration, her smartwatch kept telling her she was not being productive enough. In a new phase, the watch insists her she's had a restless night.

"I am caring for a six-month old, there's no point to be informed I'm tired," she says. "I'm acutely aware perfectly well."

Is it not possible to just stop wearing it?

"I suppose I could, theoretically, but I have this complicated dynamic with it," she says. "I appreciate it for its exercise data, but I'm unsure whether the additional features it can now do is possibly too much for me."

How Do They Work?

Different brands of smartwatch has its own proprietary way of measuring your health metrics and processing your data, but the majority use detectors on the back of the watch.

They typically project small, green LED lights onto your wrist which can detect blood flow, recording your heartbeat. Higher-end devices detect changes in the electrical current that flows through the skin to gauge your stress levels.

A Fine Balance

A professor says that for most people for smartwatches, it's a "difficult line" - while the rapidly advancing tech could potentially prevent illness, "detecting disease before we feel unwell", it could also turn us device users into the "concerned but fine".

He points out that newer wearables can conduct tests like heart rhythm analysis, which constantly monitor how normal the heart is. They can flag if someone is experiencing atrial fibrillation (AF), where there is irregular electrical activity in the heart causing an uneven pulse.

This does not necessarily indicate someone is imminently going to suffer a heart attack, but it can give an advance notice they might be more susceptible of a blood clot in the long term.

But how to interpret these readings is complicated. The expert concerns that as additional features are incorporated, people may find it hard to fully contextualise their data.

"I have some doubts that the ability to monitor so many things is such a positive development," he says.

A clinical psychologist studying cardiology agrees. Her work into the impact of wearable tech on a set of individuals with health issues suggested a minority of those who were given devices to monitor their condition experienced greater stress and were "had a higher tendency to use medical services".

She identified a vicious circle with her patients - they saw a concerning reading on their watch. They felt anxious. Their heart rate increased. They got more worried. They re-examined the data, and their anxiety increased again.

"When people are presented with data about ourselves that we can't properly interpret then, naturally, we are going to seek clarification," the psychologist says. "We check, we check again - it becomes a vicious cycle."