Recent headlines were dramatic:

⚠️ “Smartwatches can’t measure your stress levels.”
⚠️ “Your tracker is confused: stress or exercise.”

Cue the panic posts (and concerned messages from some of my coaching clients).
But here’s the truth: your wearable isn’t “confused.” And it’s not useless. The problem isn’t the tech, it’s how we interpret it.

In my Optimised Group Performance Program and with my private coaching clients, I always tell them: check in with yourself before you check your wearable. These aren’t medical-grade devices, and no algorithm should override your lived experience.

Still, dismissing the entire category because of one flawed study? That’s missing the point.

The Study That Caused the Panic (and Misses the Point)

The research behind those headlines tracked stress, fatigue, and sleep in 781 students wearing Garmin Vivosmart 4 devices — a fitness tracker first released in 2018. Participants were asked to self-report how they felt four times a day, and this was compared with the tracker’s data.

The conclusion? “Basically zero” correlation between device-generated stress scores and self-reported feelings.

And that’s when the headlines rolled in.

But here’s the issue:

• The device was seven years old.
• Only one brand was tested.
• The focus was on a narrow set of metrics.

It’s like test-driving a 2016 Mazda and declaring all electric vehicles in 2025 are useless.

Then there’s the much-quoted claim that watches “confuse stress with exercise.” That one’s especially galling, because it misunderstands biology. Exercise is stress. That’s how training works: you apply controlled stress, your systems adapt and you get stronger. A device that correctly identifies a workout as a stress event isn’t confused, it’s accurate. The real confusion lies in how the data was interpreted.
And finally, the “zero correlation” result may not prove what you think. If participants reported feeling fine while their physiology showed signs of stress, that’s not the device failing. It’s a reflection of how poorly humans judge their own state, especially under chronic, low-grade stress.

The Bigger Problem Isn’t the Tech, It’s Us

But your heart rate variability doesn’t care how you think you feel. Your body often knows before your brain admits it.

I coach countless women who see a red “high stress” alert and instantly assume the device is wrong.

But often, it’s right.

• Cortisol spikes don’t care if you feel calm.
• HRV reflects sleep debt long before your patience starts to fray.
• That “low recovery” score isn’t a weakness. It’s your biology waving a red flag, signalling you to slow down.

We often know how we feel when we physically feel stressed, but what I’ve found with many of my coaching clients, is that most people underestimate the toll that psychological stress is having on their physiology, because it’s not always as tangible.

For example, I once delivered a keynote (tracked by my WHOOP as a “stage performance”). On the surface, I didn’t feel stressed. But my biometrics told a different story: elevated strain, depleted recovery. The invisible mental load of reading the room, adjusting stories, and holding attention took a toll that I wouldn’t have acknowledged without the data.

And that’s the trap for many ambitious women: you don’t feel the toll until you hit the wall.
That’s the danger. Ignoring your device altogether, or treating its data as gospel, both rob you of self-awareness.

The Approach That Actually Works

Here’s what I tell my clients:

1️⃣ Use the data as a mirror, not a master. Let it spark curiosity, not dictate your day. Ask why you might be seeing particular trends. I encourage my clients to use the AI coach to ask about trends in your data and examine their journal (of logged activities) to unearth why these patterns might be occurring.

2️⃣ Correlate, don’t capitulate. If your device says “calm” but you feel anxious, trust yourself. If it says “stressed” but you feel fine, investigate. Your body might be ahead of your brain, or there could be a simple error. I once woke up and saw a terrible sleep score, despite feeling great and feeling like I’d had sufficient sleep. My WHOOP band had simply twisted on my arm whilst I was in bed and it hadn’t captured the data. User error.

3️⃣ Act on patterns, not moments. One high-stress reading isn’t a crisis. A week of them? That’s a pattern worth addressing. Look at the picture your wearable device is painting over time.

Practical Takeaways

If your wearable says “high stress” after a workout → it’s right. Exercise is stress (the good kind).

If your wearable says “calm” but you feel anxious → listen to your mind. Data can miss emotional drivers.

The goal is integration, not replacement. The goal is insights, not instruction. Combine objective metrics with subjective experience for the clearest picture of your wellbeing.

Bottom Line

Your wearable can tell you what’s happening inside your body.

Only you can decide what to do with it.

When you combine feeling with feedback, you stop outsourcing your wellbeing to algorithms and start leading it yourself.

That’s when performance becomes sustainable.

Reference
Siepe, J., Keller, J., Ebner-Priemer, U., & Reichert, M. (2025). Associations between ecological momentary assessment and passive sensor data in a large student sample. Journal of Medical Internet Research. https://doi.org/10.2196/12345