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There's a building tension. Apparent is the chilled vapour exhaled by my fellow runners as they perform the "starting line" jiggle on the starting line.

A quick twitch of the hips.

I'm participating in my local 5km community parkrun and I mean business. The countdown begins...

Hold on. I must sort my device. The same goes for the person alongside me.

The person waiting tuts. I'm not moving until… yes! GPS ready, and I'm running.

In the mele, it's challenging to spot a person without a smartwatch on it. And it's not just us runners who wear them.

We're witnessing a explosive, massive industry. Companies like Samsung Galaxy lead the market, each with an wide array of different versions to suit a variety of lifestyles. According to how advanced the model you go for, price tags can start from £100 to thousands of pounds.

"I find it infuriating, I can't switch off."

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

"Stop telling me about a poor sleep."

Just some of the comments I've had from like-minded tracker enthusiasts when I inquire what they feel about theirs.

The Monitoring Conundrum

My current opinion on my own device? At this moment, irritating. It's telling me my speed is wrong, making me wonder whether the trees along my route are blocking my GPS connection.

Countless individuals of us fasten these little gadgets onto our arms and keep them on constantly, apparently comfortable with the fact they're perpetually monitoring us.

Gone are the days when we depended on them exclusively to give us an estimation of our pedometer reading. Today, they can measure our nightly rest, blood pressure, heart rate variability (HRV), our recovery score.

It's tricky to find a physical metric they fail to monitor.

But can they do what they claim to do? And are the data points we analyse a faithful picture of our actual health? Do they boost our overall health, or do the multitude of readings and motivational messages just increase our daily stresses?

A Love-Hate Relationship

"I become a a little preoccupied with mine," an individual admits.

While she appreciates how her device records her runs, she finds some of its other features "excessive" at times - a feeling initially realised during a significant period.

Until she found out she could put it into a specific mode, her smartwatch repeatedly informed her she was not being active enough. Now, the watch insists her she's had a poor sleep score.

"I have a six-month old, it's unnecessary for me to be notified I've not slept," she says. "I'm acutely aware perfectly well."

Why doesn't she just remove it?

"I suppose I could, theoretically, but I'm in this love-hate relationship with it," she says. "I value it for its fitness insights, I sometimes question whether the myriad other functions it can now do is maybe too much for me."

Inside the Device

Each model of smartwatch has its own proprietary way of monitoring your vitals and interpreting your data, but the majority use detectors on the back of the watch.

They usually project tiny, coloured LED lights onto your skin which can observe pulsation, identifying your BPM. Sophisticated devices analyse changes in the bioimpedance that flows through the skin to gauge your recovery state.

A Fine Balance

One expert says that in general 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 "worried well".

He points out that newer wearables can carry out tests like medical-grade monitoring, which regularly monitor how healthy the heart is. They can notify if someone is experiencing a heart arrhythmia, where there is abnormal electrical activity in the heart causing an uneven pulse.

This does not necessarily indicate someone is about to have a cardiac event, but it can give an early warning they might be more at risk of a stroke in the future.

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

"I have some doubts that having the capacity to monitor so many metrics is such a beneficial thing," he says.

A health researcher studying cardiology agrees. Her work into the effect of wearable tech on a specific group of cardiovascular patients suggested a significant portion of those who were given devices to monitor their cardiac function experienced greater stress and were "far more likely to use medical services".

She noted a pattern with her patients - they spotted a concerning reading on their watch. They grew concerned. Their pulse went up. They got increasingly anxious. They re-examined the data, and their heart rate rose further.

"If we see stats about ourselves that we can't properly interpret then, naturally, we are going to seek clarification," the psychologist says. "We look, we obsess - it becomes a self-fulfilling prophecy."