2026年11月7日 / Last updated : 2026年11月7日 桑子 研 Science

Human Relay Race Reveals Your Nerve Speed! The Hidden Drama Inside Your Body in Just 0.187 Seconds (Sense of Touch)

I’m Ken Kuwako, a science trainer. Every day is an experiment.

You touch something hot and yank your hand away. But how long does that actually take inside your body? You can’t see signals racing through your nerves, but you can measure their speed with nothing more than a human circle and a stopwatch. All you need is the courage to hold each other’s wrists.

A Relay Through Your Nerves! How Does the Experiment Work?

The rules are simple. Everyone stands in a circle and gently grabs the wrist of the person next to them with one hand. (Middle schoolers might feel a little shy about holding hands, so wrists are a safer bet.)

One person holds a stopwatch in their right hand. They press start and, at the same moment, grab their neighbor’s wrist with their left hand. As soon as the neighbor feels the grip, they grab the wrist of the person on their other side. Keep passing the squeeze along like a relay baton. When the last person grabs the wrist of the stopwatch holder, stop the clock right away.

Say you have 10 people. Divide the total time by 10, and you get the speed of one person’s complete loop: skin, nerve, brain, nerve, muscle.

Surprising Results! How Fast Can We Think?

This time, a group of seven trainees took on the challenge, and the final time was 1.31 seconds!

Diagram showing the path of a nerve signal

Take a look at the video here.

Divide 1.31 by 7, and each person’s reaction time comes out to about 0.187 seconds. That sounds like a blink, but between being grabbed and grabbing back, your body is getting a surprising amount of work done.

What Happens Inside Your Body in 0.187 Seconds?

Here’s a question I like to ask students: “We’re going to try one more round. If everyone really concentrates, will our time get closer and closer to zero?”

That question gets them thinking about how a signal actually travels through the body. The truth is, the time can never reach zero, and the reason lies in the signal’s journey.

1. Receptors in the skin of your wrist detect the sensation of being touched.

2. Sensory nerves carry that signal up through your spinal cord to your brain.

3. Your brain decides, “I’ve been touched. Time to grab back!” and sends out a command.

4. Motor nerves deliver that command to the muscles in your arm.

5. The muscles contract, your hand moves, and you grab your neighbor’s wrist.

How fast a signal travels depends on the thickness and structure of the nerve, and the fastest ones can reach around 100 meters per second. But at the junctions between nerves, called synapses, the signal has to be converted into chemicals and handed off, and that takes time. On top of that, your brain needs time to make a decision, and your muscles need time to actually start moving. Because of these unavoidable delays, reaction time can never be zero.

By the way, the reflex that makes you pull your hand away from something hot works differently. It skips the brain and sends the command from the spinal cord, which is a shortcut. That’s why it’s much faster than the kind of reaction in our experiment, where the brain makes the call.

Touch vs. Sight: Which Is Faster?

This time we tested reactions to touch, but what about reactions to something you see? Think of a sprint race. Is there a difference between starting when you hear the gun (hearing) and starting when you see a flag drop (sight)?

定規で反応速度を確かめよう！反応時間を確かめる実験（視覚→脳→脊髄→手の動き）

It turns out the answer depends on which sense is involved. Each one sends information along slightly different pathways, and the brain processes it differently, so reaction times vary. In general, reactions to touch and sound are said to be a little faster than reactions to sight. If you dig into how we react to what we see, you’ll find even more fascinating discoveries.

目で見てからでは間に合わない！お札キャッチで学ぶ「0.2秒の壁」の正体（反応速度）

Try It Together!

You can easily do this experiment with family, friends, or your whole class. Try changing the number of people, or tapping shoulders instead of grabbing wrists, and see how the time changes. Come up with your own questions to explore, like “Will we get faster on the second try?” or “If we add more people, does each person’s time change?” Asking and testing your own questions is a wonderful way to learn.

Contact and Requests

Science is full of wonder and fun, and I want to bring it closer to everyday life! This site is packed with science experiments you can do at home, along with tips to make them work. Have a look around and search for whatever sparks your curiosity!
・Learn more about the site’s author, Ken Kuwako, here.
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  • 『高校入試 分解問題集 理科』（学研）…難しい問題も小さな問題に分解することで、問題を解くことができます。そんな分解の技術が身につくように深く関わりを持って作りました。
    『大人のための高校物理復習帳』（講談社）…一般向けに日常の物理について公式を元に紐解きました。特設サイトでは実験を多数紹介しています。※増刷がかかり６刷となりました（2026/02/01）
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  • 『きめる!共通テスト 物理基礎 改訂版』（学研）…　高校物理の参考書です。イラストを多くしてイメージが持てるように描きました。授業についていけない、物理が苦手、そんな生徒におすすめです。特設サイトはこちら。

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