12 Months to Marathon - Episode 56 - The Danger of Data

Let’s be honest, these devices are amazing. I love my Garmin. Heart rate zones, VO2 max estimates, sleep tracking, HRV, race predictions, it’s all powerful stuff. And it can help guide our training in meaningful ways.

But there’s a fine line between using the data and being used by it.

When you start planning your day based on whether your watch says you slept well… or skipping a session because your 'body battery' says you're tired, even though you feel great, you’re crossing into dangerous territory.

These devices are tools, not truth.

Let’s go back to last night. My watch missed a full hour of sleep. Just glitched out. But my body didn’t glitch, I had that hour. I woke up feeling fine. Yet my watch told a completely different story. So what do I believe? The tech? Or my own experience?

Here’s the danger:

• You start second-guessing yourself.
• You become reactive instead of intuitive.
• You override your own internal signals.

That’s when the numbers start driving the narrative. And you stop listening to your own body, which, by the way, is the only system that actually matters on race day."

Real Training Happens in the Body, Not the Watch

"You don’t race with your Garmin telling you when to push or when to ease off. You race with your lungs, your legs, your grit"

Data can’t account for everything:

• The quality of your nutrition
• Your stress levels
• A fight with your partner
• A bad night’s sleep followed by a surprisingly good run

We’ve all had days where the numbers said we should feel awful, but we crushed the workout. And the opposite—when the metrics look great but the run feels like molasses.

So what gives?

The data is a snapshot—but it’s not the whole picture. That’s why we need to anchor ourselves back to one key question:
How do I feel today?"

Using Data Without Becoming a Slave to It 

Look, I’m not saying throw your watch in the bin. I’m still using mine. I love training zones and long-term trends. But I’m starting to put the numbers in their proper place, as a guide, not a gospel.

Here’s what I try to do now:

• Start the run by checking in with my body—not my watch.
• Let heart rate confirm effort—not dictate it.
• Use sleep data to notice trends—not determine mood.
• Be okay with 'off' data days.

One dodgy night of sleep tracking doesn’t mean your body is broken. Just means the watch had a hiccup.

So if you take one thing from today

 Don’t let data override your instincts.

Remember to follow me on Instagram for all your running content 

https://www.instagram.com/12monthstomarathon 

JH