The Triathlete Blueprint Newsletter #121-Garbage In, Garbage Out: How to Avoid the Data Traps in Triathlon Training

Yan Busset
Aug 23, 2025
4 min read

Read time: 4min.

By Coach Yan Busset

Guidelines for Clean Data That Could Save Your Training

Technology in triathlon has always been there but now more than ever, its exploding. Power meters, heart rate monitors, glucose sensors, sleep trackers, lactate testing… Never before have athletes had access to so much data. And that’s fantastic, I’m all in for it. But as with every tool, it’s only as good as the quality of the data you collect.

Garbage in, garbage out. That saying applies more than ever.

This article isn’t a rant against wearables. It’s a guide to using them smarter. Because sometimes, a tiny setup mistake or a false assumption can throw your entire interpretation off. Let’s go through the most common devices and see what to be aware of, plus a few small tips to help you collect cleaner, more reliable data.

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Heart Rate – the OG of endurance metrics

It’s the OG of endurance metrics. While it’s not my go-to tool for pacing, it still has value when used correctly. I mainly use it to monitor recovery, and it’s particularly useful during zone 2 assessments to detect cardiac drift. But remember, heart rate is not a real-time metric—it lags on short efforts and can be affected by fatigue, heat, caffeine, hydration, and stress.

👉 Take-away tip: If you’re using wrist-based HR, make sure your watch is snug and stable. Otherwise, your readings can be completely off. A chest strap or optical armband is a safer bet for consistency.

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Power Meters – precise but not absolute

What´s your FTP? Is maybe one of the first question we ask between AGs. But don’t treat power it as a universal truth. Your power zones are only valid with the same power meter, in the same position, on the same bike setup. Swap any of these, and your zones can be off. Even two same high-end power meters can show a 2% gap..

👉 Take-away tip: Always calibrate your power meter regularly, double-check crank length settings, and stick to the same device for progress tracking. Don’t use WattBike test results on your tri bike without re-testing.

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Glucose Monitors – an exciting technology still evolving

Real-time glucose monitors are gaining popularity among endurance athletes. They measure glucose in the interstitial fluid, which causes a slight delay compared to blood glucose. That makes them more suitable for post-session review than live decision-making during a workout. But for spotting patterns in your nutrition, stress, and energy response—they’re promising tools.

👉 Take-away tip: Use glucose monitors for trend analysis after training, not for real-time fueling adjustments. Understand the lag, and don’t panic if you see a dip or spike—it might already be outdated.

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Lactate Testing – powerful, if done properly

Lactate testing is nothing new, but it’s trending again. It’s a great way to understand aerobic vs anaerobic effort—but only if done right. Errors are easy: not enough blood, sweat contamination, bad strips, or taking samples at the wrong time. One or two samples don’t mean much, you need consistent protocols over time.

👉 Take-away tip: Always clean the area, take sample on the same spot,same device and repeat the protocol under the same conditions. Lactate is a great tool, but not magic. Poor sampling gives poor insights.

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Sleep & Recovery Trackers – good for trends, not absolutes

Most wearables now provide sleep scores, HRV, and recovery ratings. These can give a general idea of how you’re coping with training. But don’t overinterpret them—sleep phase tracking is often inaccurate, and one bad score doesn’t mean you’re broken.

👉 Take-away tip: Focus on long-term trends and how you actually feel. One low score doesn’t define your readiness, use the data to support your intuition, not replace it. Track your average weekly sleep time for a more reliable recovery value.

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Training Stress Scores – useful but not always aligned

Training platforms often calculate their version of a TSS (Training Stress Score) based on power, pace, or heart rate. It works fairly well in cycling thanks to power meters, okish for running. But in swimming, where measurements are less precise, the scores can be misleading, and it can affect your vision of the actual workload when you look at the global CTL (chronic training load).

👉 Take-away tip: Use CTL and TSS as directional indicators, not as absolute truths. Especially if your swim or run data isn’t based on consistent metrics, take the overall picture with a grain of salt.

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Testing – compare apples to apples

A lot of confusion comes from changing testing protocols too often. Doing an FTP 20-minute test one week, a ramp test the next, and a lab test after that… it creates noise instead of clarity. Every protocol gives a different result—you need repeatable conditions to track progress.

👉 Take-away tip: Stick to the same testing method over time. Use the same conditions, same gear, same warm-up, and test regularly. That’s how you see true trends.

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All these tools—heart rate, power meters, glucose sensors, sleep trackers, lactate monitors—can be fantastic when used with perspective. The key is not to reject them, but to understand their strengths, their limits, and the best ways to use them.

Whatever coaching style you follow, whether you’re training with a coach, through a platform, an app or on your own—data is only as good as the system you build around it. Know what to trust, how to cross-check, and what each tool is really telling you.