To track our progress without stopping, we must accept a margin of error.

Listen to your pulse

Chapter 1

The science of the beat

Chapter 2

The tech on your wrist

Chapter 3

Training by the numbers

Chapter 4

Beyond the watch

Ch 2 · The tech on your wrist
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coach Smartwatch Pulse Oximetry

Red and infrared, red and infrared, counting the oxygen riding on your cells.

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The magic of green light

coach Your watch's optical sensor uses photoplethysmography to translate rapid changes in capillary light absorption into your real-time pulse.

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Quiz

Why do smartwatches use green LED lights to measure your heart rate?

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Quiz

What is the scientific name for the optical technology smartwatches use to detect blood volume changes?

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To track our progress without stopping, we must accept a margin of error.

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The Finnish skiing origin story

coach Polar Electro introduced the first wireless wearable heart rate monitor in 1982.

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Quiz

Which company, founded by Seppo Säynäjäkangas, released the first wireless wearable heart rate monitor in 1982?

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Quiz

In which country was the wireless portable heart rate monitor invented in 1977?

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Fun Fact

Wearable tech: The first Garmin GPS fitness watch, released in 2003, was so large that athletes joked it looked like wearing a brick on their wrist.

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Quiz

What technology do chest strap heart rate monitors use to detect your heartbeat?

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Quiz

Why can wrist-based optical sensors lag during sudden high-intensity sprints?

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Gossip

Would you wear a smart ring?

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Quiz

Which light wavelengths do smartwatches use to estimate your blood oxygen levels?

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Quiz

What does the abbreviation SpO2 represent on your fitness wearable?

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