The Power of Prostheses

Read on for the story of Professor Hugh Herr, a physicist who once dreamed of being a rock climber. All words in bold can be found in the glossary at the end of the story. Questions and resources can also be found after the glossary. Happy reading!

A drawing of a young, white man (Hugh Herr) with brown hair climbing a grey rock-face. He is wearing a green t-shirt, blue trousers, and red boots. He is smiling.

Meet Professor Hugh Herr. He’s a physicist from Pennsylvania in the USA. 

Hugh is a scientist, but science isn’t his whole life. Just like you, me, or anyone else, he has hobbies, dreams, and activities that he loves to do outside of work. 

When Hugh was a young boy, before he ever thought about physics, he loved rock climbing. The mountains near his home were a playground for his family, and spending time outdoors was his favourite thing to do.

As a teenager, Hugh was considered one of the best climbers in North America. He was determined to become a professional rock climber, and spent all of his spare time training with his friends. He was fearless, and adventured on incredibly challenging routes for a climber his age.

That is, until one day in January 1982, when his dream came to a crushing halt. 

After completing a difficult and dangerous climbing route through an icy ravine, Hugh and his friend Jeff Batzer were caught in a blizzard on the top of an isolated mountain. The snow was so heavy that the two boys became completely lost, left to huddle together on the mountain to try to keep warm. 

The storm was so bad, and the mountain so dangerous, that it took three days for rescue teams to find the boys. They both survived, but had suffered severe frostbite because of the incredible cold. Both of Hugh’s legs were so badly damaged, that they had to be amputated at the knee, leaving him unable to walk – or climb. 

He was just 17 years old. 

A drawing of Hugh after he has been given prostheses for the first time. He is wearing red trousers, which are rolled up to the knee. He is standing on grey prostheses, which end in green shoes, and using two crutches to help himself walk.

It took Hugh many months to recover from his injuries, and he had to relearn how to walk. When he asked his doctors if he would be able to climb again, they told him that it was unlikely. 

But Hugh was still the determined boy that he was before the accident, and he set his mind on a new ambition. Before the accident, he’d never been much good in school. He didn’t work very hard, because he’d been so focused on the sport and climbing that he loved. Now, he was inspired to work harder than ever before. He found a new love for physics and engineering – looking at how things work, and how machines are designed.

While he was at college studying physics, Hugh discovered a new hobby. He loved to design and redesign his new prosthetic legs, finding ways to make them better and more efficient each time. 

A text box. It reads: 
A prosthesis (pros-thee-sis) is the name for an artificial limb. Instead of saying prosthesis, or prostheses (the plural), people often describe limbs as being ‘prosthetic’(pros-thet-ic) – for example, “prosthetic leg” or “prosthetic finger”.
Prosthetic limbs act as replacements for real limbs. There are a lot of reasons why a person might be missing a limb. Some people, like Hugh, have limbs removed after life-changing injuries or illnesses, while other people are born without certain limbs.
Your limbs are made up of lots of parts, which make them move the way that they do, so prostheses have lots of different parts too! Just like your legs have different bones and muscles that make them work, prostheses have lots of complicated components. 
There is a drawing of a prosthetic leg here. It shows the many different parts - from foot, to ankle, to a shin, and a large hole where the knee is inserted. 
Designs for prostheses are improving, and many are controlled by clever computers that are small enough to go inside them. Some people, like Hugh, have several different types of prosthetic leg, so they can choose the right one for the activity that they want to do!

Hugh realised that, because his legs were adjustable and made of metal and plastic rather than skin and bone, he wasn’t limited by his natural height. He could make the prosthetic legs any length he wanted, by changing their design. This led to some very funny events, including a party where he wore legs that made him over 2.5 metres tall! That’s probably more than double your height, and much MUCH taller than most adults! 

A drawing of three men. Hugh is in the centre. The other men are only tall enough to reach his elbow, because Hugh is wearing long black prostheses. All three men are dressed in suits, as if they are at a fancy part or event. Hugh's suit trousers are cut at the knee, so his prostheses are on display.

After he finished his physics degree, Hugh wanted to keep working on his exciting new prosthetic designs. He recognised that they could make a difference not just to his own life, but to the lives of thousands of other people too. 

Hugh started to work on much more complicated and clever designs for his own prostheses, far beyond just changing his height. He didn’t like his original prostheses, because they didn’t move like natural legs. To take part in sport, or even to just move around like he could before he lost his legs, Hugh needed to create prostheses that were adaptable and moved in a natural way.

With time, Hugh worked hard on these designs, creating increasingly clever prostheses that pushed the boundaries of what artificial legs had previously been able to do. He created specially-made legs that allowed him to stand on tiny ledges, and ones with titanium spikes that helped him climb steep ice walls – all in the hope that they would allow him to climb again. 

Hugh worked and worked at his designs, perfecting every tiny detail until finally, he created prostheses that were able to act like his legs had, giving him the flexibility and strength that he needed.

One incredible day, all this hard work paid off, and Hugh was once again able to rock climb. 

With practise, his old skills came flooding back, until he was once again a good climber. So good, in fact, that his friends accused him of cheating! They said that the prostheses actually gave him an advantage, because they were so well designed. 

Hugh is climbing a grey rock-face once again. This time, he is wearing a blue shirt, orange trousers - and his prostheses, which end in red shoes.

It wasn’t just Hugh’s friends that thought this. Soon, Hugh was climbing at a more advanced level than he had been before the accident. He competed with able-bodied climbers, at the same elite level that he had been forced to leave after his accident. 

So, despite everything that had happened, Hugh was still able to achieve his old dream. He was still an amazing climber, and still able to compete just as he had before the accident. 

But now, he had a new, bigger dream. 

Rock-climbing was no longer enough for Hugh. He knew that his designs could help more people, and because he’d dedicated himself to studying physics after his accident, he had all the training he needed to go out into the world and make a difference.

Now, Hugh is a biophysicist. He studies how our brains communicate with the rest of our body, enabling us to move our natural limbs, and then tries to replicate these processes for people with prosthetic limbs, by designing complicated machinery.

In modern life, not having a limb can make a real difference to what you are able to do. Imagine trying to play the piano with one hand, play football with one leg, or brush your teeth with no arms. You could definitely still do these things – but it would be much harder for you to do them as efficiently as a person who has all their limbs. 

This is why scientists like Hugh want to make prostheses that act just like real limbs.

A drawing of three disabled people. There is a man sitting in a wheelchair, who has lost both his legs below the knee. Beside him is a woman who is standing using crutches. She has lost one leg to mid-thigh. In front of them both is a young man, who has lost both hands at the wrist.

If you wanted to play football, but only had one leg, it would help a lot to have a prosthesis that you could lean on like a real leg. It would help even more if the prosthesis was flexible, and allowed you to run and twist and jump. 

But if you could control this prosthesis with your brain, just like you control your own legs that are made of muscle and bone, then you’d be able to play football just as easily and effectively as an able-bodied player. 

This is what Hugh and his team are hoping to achieve with their latest designs.

A drawing of two able-bodied football players. In front of them, a yellow-haired boy with prosthetic legs below the knee runs past, dribbling a football.

They have set themselves an incredibly hard task. Our bodies are mind-bogglingly complicated. We control our limbs by making hundreds of thousands of decisions that affect when and how each part moves. These decisions happen super-fast – it doesn’t seem like you even think about moving your arm to touch your hair, or your leg to tap your foot, but in reality, every movement takes a lot of brain power! 

A text box. It reads:
The Nervous System 
Throughout every part of your body runs a tiny electrical highway known as The Nervous System. It’s made of billions of cells, which are joined together to make nerves. Through the nervous system, your brain is able to keep track of everything that’s happening in and around the body. It can also send messages through the system. 
To move a limb, a message from your brain has to travel down nerves to the muscles that control movement. The messages are transferred from cell to cell through electrical signals that can move incredibly quickly through the body!
To the left is a drawing of the human body, showing that the nervous system runs through every part of it.

The nervous system is made up of lots of living cells within your body. Being able to send electrical signals through these cells is part of what makes us alive. Our brain controls our body via these signals, and to do so it is dependent on the network of nerves that runs through our limbs. This is why, in the past, prostheses could not be controlled by the brain. 

Think of a pirate with a wooden leg. The leg is sturdy and does a good job of helping them to stand up. Without it, they would be more negatively impacted by their missing limb. However, they cannot control it. The leg is something outside their body – it is no more a part of them than a shoe is part of your foot. 

Hugh dreams of limbs which can tap into the electrical messaging system inside your body. Prostheses today are nothing like wooden pirate legs – they are bionic, and contain tiny computers that control the movements of their many parts. If the messages from these computers were able to connect up with the brain’s electrical messaging system, we could control them as if they were a real limb. This would be a huge breakthrough for people who need prostheses!

A drawing of a persons head, arms, and torso, showing nerves running throughout the body. One arm has a prosthetic hand and arm up to the elbow. This is seemlessly joined to the rest of the nervous system.

After years of hard work, Hugh and his team eventually created a new medical technique called AMI. When a person loses a limb, AMI can be used to make sure that the remaining muscles in their body can communicate with a specially designed prosthesis. This means that people with AMI are able to feel the positions and movements of a prosthesis, and control it like it’s their own limb.

AMI was first tested on Hugh’s friend Jim, who had also been a climber before he lost a leg. Just a few hours after his operation and the fitting of his new prosthetic, Jim was able to make gestures with his foot, and could soon climb up and down stairs with the leg bearing his weight! AMI allowed Jim’s brain to control his prosthesis – he could move it in just the same way as he could his other leg.

When Hugh asked Jim how he felt about his new prosthesis, he said “the robot became part of me”.  Hugh had successfully created a prosthesis that felt like it was meant to be there. He used technology in a new, incredible way, that made Jim feel like his leg wasn’t just a tool that he could use to walk, but a part of his identity.

A drawing of a man bending over as if to pick something up from the floor. He has prosthetic legs up to the knee and is wearing blue shoes.

It takes a very long time to create prostheses like this. They have to be tailored to each individual person who needs one. However, this incredible discovery takes us a step closer to making sure that when a person loses a limb, the replacement can be as effective as possible, letting them keep the opportunities they had before. 

What an accomplishment! Not only had Hugh achieved his new, bigger dream, but his inventions have contributed towards thousands of people with prostheses being able to achieve their dreams, too. 

Thank you for reading!

This story was written as part of a Masters in Science Communication project, investigating whether storytelling is an effective way to teach children about science and scientists. As a result, I would really appreciate some feedback, which you can give by answering a short survey. The survey takes less than 5 minutes to complete, and I will use the results to develop even better science stories in the future. To help, just click on the button below.

A text box. It reads:
Adaptable – able to change and adjust to new conditions
AMI – AMI stands for agonist-antagonist myoneural interface. This is a method designed to give a person awareness of the position of their prosthetic limb. Because of AMI, their brain can receive electrical messages from the prosthesis and send messages back that tell it what to do. It allows people to ‘feel’ their prostheses, and move them like natural limbs. AMIs are created from muscles, during amputation surgery.
Amputated – an amputation is when a limb is intentionally removed by a surgeon. When the limb is removed, we say that is has been amputated.
Artificial – made or produced by humans, rather than occurring naturally. 
Bionic – we say that body parts are ‘bionic’ when some element of them is artificial, usually electrical. Bionics is the study of mechanical systems that act like living things, or parts of living things.
Biophysicist – a scientist who studies how the laws of physics can be applied to biological things.
Efficient – something is efficient when it is as successful as possible, and has minimal wasted effort or cost.
Electrical signals – tiny pulses of electricity that carry information.
Frostbite – an injury caused when parts of the body freeze due to extreme cold. 
Muscles – parts of your body that contract and relax to cause movement.
Nerves – bundles of fibres that electrical signals pass through within your body. They connect your muscles to your brain, so that messages can be passed between them.
Prosthesis – an artificial body part
The Nervous System – a network of nerves that carries electrical signals all round your body. 
Titanium – a hard, silver-grey metal that is strong but not heavy.
A text-box. It reads:
Hungry for more? 
If you’ve loved hearing about how Hugh used physics and biology to make life-changing new designs, have a think about these questions…
1.	To be able to rock climb, Hugh had to give his prostheses certain properties that made them suitable for the job – just like you’d choose to wear trainers to play sport rather than fancy shoes! What kind of properties do you think his prostheses needed? How would you create the best possible design for rock climbing? Hint: watch the videos above to have a look at Hugh’s designs!

2.	When Hugh first started to play with the design of his prostheses, he created some that made him taller! However, he doesn’t use these at all now. Why do you think that many prostheses try to act as much like natural limbs as possible, rather than being wacky and new? 

3.	At the moment, the main purpose of prostheses is to help people who have lost limbs. But, as Hugh found out, prostheses can help people be not just as good, but even better at things than before. This led him to wonder about how able-bodied people, too, could use bionic limbs. Think about how a prosthesis could help you, and what it could look like – could you run faster, reach higher, or even do something super-human, if your limbs were made more effective by technology?

4.	Sometimes, your nervous system allows your body to react to things without you even thinking about it. This is called a reflex reaction. A good example is when you accidentally touch something hot, and your body immediately moves away. Can you think of any more examples? How do you think your body controls this reaction? 

5.	We know that the nervous system is made up of thousands of nerves, but what do you think nerves are made of? What special properties might they need to have, to make sure that electrical signals can travel along them?


Hugh’s research paper: Clites, T., Clarty, M., Ullauri, J., Carney, M., Mooney, L., Duval, J., Srinivasan, S., Herr, H. (2018). Proprioception from a neurally controlled lower-extremity prosthesis. Science Translational Medicine. 10: eaap8373.

More information about Professor Hugh Herr:

Video: “Ascent – The Story of Hugh Herr”

Video: Hugh talks about how new prosthetics allow people to run, climb, and dance.

Article: Hugh’s life and work

More information about prostheses:

Video: Hugh’s prostheses in action

Video: Jim moves his new prosthetic after surgery

Video: Jim rock-climbing with his new prosthesis

Article: Prosthetic Limbs

Article: Prostheses through history

More information about the nervous system:

Article: What is the nervous system, and how does it work?

Video: How do nerves travel through your body?  *Warning: contains real body parts!


The research was produced not just by Hugh Herr, but also by the other members of his research team: Tyler Clites, Matthew Carty, Jessica Ullauri, Matthew Carney, Luke Mooney, Jean-François Duval, and Shriya Srinivasan. They too deserve credit for this discovery – good science is often best done as a team.  

This story would not be nearly so good without its illustrations by the wonderful Sofya Tamarina, and the advice and support of Dr. Nicola Hemmings. Thank you!

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