Hands up!

  • They may look fragile, with their slim bones and complex joints, but hands are surprisingly tough and amazingly versatile.
  • Hands up!
  • Fingers operate at a mechanical disadvantage, so the tendon connecting the bone of your fingertip to the muscle in your arm must pull with a strong force to resist a small force applied to the fingertip.
  • When you have a quiet moment, take some time to learn how your hands are put together. Locate the tendons, ligaments and wrist-bones, and manipulate them to see how they work. You"â„¢ll emerge with a new respect for these everyday tools.
  • Although they"â„¢re not quite there yet, scientists are making good progress in their efforts to create a robotic hand that mimics the movements of the human hand. And in a significant breakthrough last year, Japanese researchers demonstrated a robotic hand controlled by the power of thought alone, taking its cue from real-time functional magnetic resonance imaging (fMRI) of their brain activity. The system was developed by Yukiyasu Kamitani and colleagues at the ATR Computational Neuroscience Laboratories in Kyoto, together with researchers from the Honda Research Institute. As subjects lay inside an MRI scanner, they were asked to make "rock, paper, scissors" shapes with their right hand while the scanner recorded their brain activity and fed the data to a computer. After a while, the computer was able to "recognise" the brain activity associated with each shape, and command the robotic hand to replicate the movement.
Date:31 January 2007 Tags:

While hanging from Fairview Dome, a rock-climbing physicist contemplates the mechanics of his hands

I was shivering in the pre-dawn cold at the base of a 300 m granite wall in Yosemite National Park, USA. My palms were wet with nervous sweat. In a few minutes I was going to start climbing the wall, and I didn’t know whether I would make it to the top or not.

The route I had chosen is known as the Regular Route on Fairview Dome. It’s a hard route, but nowhere near the hardest by modern rock-climbing standards. By my own standards, however, it was bigger and harder than anything I had ever attempted. Whether I made it to the top would depend on the co-ordinated work of my brain, my feet and my hands.

While my eyes studied the steep crack that marked the line of my route, my hands tightened my bootlaces and my harness straps, then tied the knot that attached a nylon rope to my harness. The harness was made of 5 cm-wide nylon straps, like the safety belts in a car, and had the same purpose: to stop me when I was moving at a high speed without injuring me in the process.

As I followed the familiar ritual of dressing like a climber, my fear decreased, my hands stopped sweating, and I began to savour the thought of a fine climb. Beside me, Mike tore adhesive tape from a roll and wrapped it around his hands. He looked up at me from his seat on the ground and smiled. I smiled back. We were both thinking the same thoughts, a combination of “We do this for fun, right?” and “Whose idea was this, anyway?”

On the upcoming climb, our hands, more than any other body part, would be tested to their limits. My life would be in Mike’s hands as much as my own. If I fell, he would have to hold the rope and stop my fall. The job of my hands would be to make sure I didn’t fall.

Open the bonnet of a car and look at the complex mess that fills the frame: pulleys, hoses, cables, wires and engine block. My hand has equivalents to all of these pieces packed into a much tighter space: the bones provide an internal frame; arteries and veins are the plumbing, bringing in the fuel and oxygen and removing waste; nerves – like the wires of the car – carry both control and sensory signals; muscles provide the power; and tendons are the cables connecting the muscles to the bones. All of these pieces are laced together with ligaments and wrapped in skin.

I stepped up to the rock and began to climb. In climbing terms, I was the leader. Before long, the ugly pink, orange and black rope snaked down 9 m from my harness, around Mike’s hips and to his right hand, where he held it in a power grip. The types of hand grips have been classified by the English physician John Napier: the two most common are the power grip and the precision grip. The power grip squeezes an object strongly between the pads of the fingers and the palm, allowing the full strength of the forearm muscles to be applied.

In the precision grip, you use just the tips of your fingers. This grip is suited to fine control, and is used to start the threads of a peanut butter jar lid turning, and then switch to the power grip when you wanted to seal it tight.

Mike’s grip wasn’t doing me any good at the moment. If I fell, the rope and I would crash to the ground below. It was time to do something to ensure my safety. I selected a small wedge of aluminium, which climbers call a chock, from the dozen or so different sizes that I carried with me.

Using the precision grip, I wedged the chock into a 6 cm-wide crack in the mountain. The grip gave me the precise control I needed to make sure that this chock was placed well enough to withstand shock loads that could be as great as a ton. I used a snap link called a carabiner to attach the rope to the chock and continued climbing, feeling more at ease. Now if I fell, the rope would come tight after I dropped past the chock, and Mike’s hand could stop my fall. Once chocks are in place, climbers call them “protection”.

If I slipped off the rock when I was 5 m above my chock, I would fall 10 m and would be going 50 km/h when the rope came tight. The rope would bring me to a stop rapidly, stretching in the process and pulling on me with a force several times larger than gravity. Since gravity pulls me down with 68 kg of force, the rope might have to exert as much as half a ton of force on me. Mike would then have to hold the other end of the rope against that half-ton of force.

Wait a minute! How can the grip of a single hand provide the hundreds of kilograms of force needed to stop a falling climber? When Mike’s hand, in a power grip, squeezes the rope the friction of the rope against the palm of his hand (or his tape on today’s climb), exerts over 45 kg of force, but that is not enough to stop my fall. However, the rope also wraps around Mike’s hips, and the friction of the rope around his hips amplifies the force of his hand several times.

Force amplification provided by the friction of a rope running around a cylinder is known as a belay. (The belaying pins in old pirate movies had ropes from the rigging of the ship wrapped around them. Friction of the rope around the pin held the rope in place.)

I climbed on, secure in the knowledge that if I fell, I wouldn’t hit the ground – as long as the chock didn’t pop out of its crack. I climbed using the hook grip, the same grip you use to carry a briefcase. But I was using the hook grip in reverse – to hold me up.

In the hook grip, the last two joints of my fingers were bent over and placed on a small ledge of rock about 6 mm wide, the width of a piece of cassette recording tape. Although the hook grip could hold my entire weight, it usually shared the load with my feet, which found small footholds. To John Napier, the hook grip was a secondary grip, but to a climber or a monkey swinging through the trees, there is nothing second class about it. It is the most-used grip.

When I found a hold that was not wide enough to allow me to get all of the fingers of my right hand on to it at the same time, I placed my three middle fingers on the hold, then stacked the thumb and little finger on top of them. I was pleased that I had learned a few tricks in my years of climbing, but my pleasure faded when I noticed that I needed the very same hold for my left hand. With the delicacy of a concert pianist (but at about one-hundredth the speed), I removed one finger at a time from the ledge and replaced it with a finger from my left hand. Successful, I reached up for the next hold with my right hand.

Ten storeys above Mike, I was nearing the hardest move on the climb, the part that climbers call “the crux”. The rock got steeper and smoother, and the holds grew scarcer. There seemed to be no hand- or footholds. The crack I had been following pinched down to a thin seam. My fingertips searched across the blank rock to my left, feeling nothing at first. Finally, they found a rough spot suitable for use as a foothold.

My fingertips are capable of feeling a groove or surface roughness only 0,000254 mm deep. Here, on the cliff, my sense of touch had found a hold that was too well camouflaged for my eyes to see. Climbers need a good sense of touch. The callouses that a climber develops from continual climbing interfere with this sense of touch, which is why some top climbers can be seen sitting around the campfire sanding their callouses away like safecrackers in an old B-movie.

One terrible foothold was not going to get me up over the next stretch of steep rock, so I continued groping for a better hold. There was a small spot in the crack, wide enough to take two fingertips, so I put two fingers into the hole. Bad news – it was wet. Moist skin has a better grip than dry skin. (That’s why loggers spit on their hands before wielding an axe, and is one reason that my fingertips have sweat ducts.) Too much moisture, however, acts as a lubricant.

Unfortunately, I was in a tight situation, and my palms and fingertips had begun sweating in response to emotional pressure. The last thing I wanted to d
o right now was to add my sweat to the wetness of the crack. It was wet enough. My fingertips have papillary ridges, which make up my fingerprints. Like the tread on a car tyre, these fingerprint ridges improve the friction of my grip, but not enough to get me past the wet section of the climb.

Some climbers carry a small bag of gymnast’s powdered chalk with them. A quick dip of their hands into the chalk dries the hands, and coats them with a thin layer of abrasive material that improves their grip. At that moment, I almost wished I were a climber who was willing to use chalk.

I kept looking around for better holds, but my search was fruitless. I was going to have to move up on the friction of a poor foot smear and the pull of two fingertips jammed into a small, wet hole. My last protection was just below my feet. I put my fingers in the hole, stepped up with my foot, and pulled. My fingers began to ooze out of the crack, so I quickly lowered myself back to see if I could find some more holds. Mike patiently held the rope and shouted encouragement. After all, if I couldn’t lead the crux, he would have to.

Climbing exerts tremendous forces on fingers. I remembered when my friend Hal was doing a two-finger layback, just like the one I was about to try. (In a “layback”, a climber pulls himself into a hold on a steep wall with his hands and then walks up the wall.) One of Hal’s fingers slipped off the hold. Suddenly, the remaining fingertip was loaded with most of Hal’s weight. He heard a loud “Kapow!” as the tendon that connected the muscle to the fingertip of his middle finger ripped, and he fell.

A doctor found later that the tendon was only partially ripped. For two weeks, Hal’s finger ached. It was six weeks before he could brush his teeth without noticing the weakness in the last joint of his finger. It was over a year before his finger had recovered its pre-accident strength. Tendons heal slowly.

My mind wandered while my fingers searched for a hold. I thought about my fingers. A lever operates at a mechanical advantage; it can amplify a few kilograms of force moving over a large distance into a large force moving over a small distance. Fingers, however, operate at a mechanical disadvantage. The tendon connecting the bone of the fingertip to the muscle in the arm must pull with a strong force to resist a small force applied to a fingertip. The 45 kg exerted on Hal’s fingertip was amplified to several hundred kilograms of tension in Hal’s finger tendon and muscle. That was enough force to rip the tendon.

At first glance, the human body seems to be built wrong: the levers are backwards. Consider the elbow. When you hold a can of cola in your hand with your elbow bent at a right angle, the weight of the can pulls the lower arm down, pivoting it about the elbow joint. The bicep muscle pulls up on the lower arm, fighting gravity and holding the arm in place But, as anyone who has used a lever knows, the farther the force is from the pivot, the greater the twisting force, or torque, it exerts.

If you push on a door at the knob, it pivots easily on its hinges. But try pushing a door open with your hand placed only a few centimetres from the hinge. The closer your hand is to the hinge, the more difficult it is to open the door. Similarly, the can is five times further from the elbow than the bicep attachment. To hold up a 1 kg can, the bicep muscle must pull up with 5 kg of force.

The whole human body is designed this way. Almost every muscle, including those of the hand, works at a mechanical disadvantage. The muscle must exert more force than the weight opposing it. Why? The real problem is that muscles cannot move very far. As it is, the muscle must exert 5 kg of force to lift a 1 kg can. But if the can is lifted 30 cm, the muscle only needs to contract by 6 cm. If the body were designed with a mechanical advantage of five, then the muscle would only have to pull with one-fifth of a kilogram of force, but it would have to contract over 1,5 m, and our elbows would drag across the ground!

After all these musings, I still hadn’t felt another hold. I could see a narrow slot just above me, out of reach at the moment. If I could just get my fingers into it, I thought, I would be over the crux. I put my foot up and pulled again. The muscles in my forearms pulled with a half ton of force and lifted me slowly up, working at a disadvantage against gravity.

My other hand reached up and then jammed into the enticing hold. It wasn’t a hole at all, just a rounded slimy place. I was in trouble. I had foolishly assumed that it would be a good hold, and I was wrong. Since I had moved up, I couldn’t pull my body into the rock as strongly as before, and my foot began to slip. My free hand rapidly searched for invisible holds and, luckily, found one: a single rough crystal. I smashed my index finger down on to that crystal and piled the other fingers and thumb of that hand on top of it. Then I pulled up, easing the load on my foot.

My other foot felt out to the right, looking for holds. No luck. Trusting the finger pile, I let go of the wet hold and reached up further. At last, my fingers slipped into a crack and I began to feel better. A quick pull and I was above the crux. I found good footholds, placed some protection, and let out a yell.

In a few more metres, I arrived at a ledge big enough to sit on. I tied myself to the mountain and called “Off belay!”, letting Mike know that my life was my own responsibility again. I wrapped the rope around my waist, grabbed the rope in a power grip, and called, “On belay!”. Mike followed me up the climb. He flowed up in great style, but I was secretly pleased when he slowed down a little at the crux. He joined me at the belay ledge and we shook hands.

He said, “Nice lead, PD”, which translates into, “I noticed the crux and I’m glad it was your lead”. I was ecstatic. After all, we had come one-tenth of the way; we only had 275 m to go!

It was Mike’s turn to lead. The crack was bigger now, big enough to swallow an entire hand. Mike didn’t need to use any of Napier’s grips. Instead, he jammed his entire hand into the crack, using it as a wedge, to hold his weight. Dr. Napier would probably have cringed at what Mike was doing to his hand, but the hand jam held Mike firmly in place, attached to the mountain.

The biggest problem in climbing jam cracks is the pain. As a simple machine, the wedge is an excellent force amplifier. You can split a log with a wedge and a sledgehammer because the shape of the wedge amplifies the downward blow of the hammer and directs it outward. When a climber uses a hand as a wedge to support his weight, a force much greater than his weight is transmitted through the hand to the rock.

The hand wedge tries to split the crack apart. This force is applied directly through the skin to the rock of the crack. Usually, the crack does not split open. The rock pushes back on the skin with a force that is large enough to be painful, and may even cut the skin if there are any sharp crystals in the crack. I was glad Mike was leading now, since he had wrapped his hands in adhesive tape to protect his skin from abrasion.

Skin is amazing. The folds in the skin on the back of a knuckle allow the skin to unfold to 1,8 times its original length before it begins to stretch. It can then stretch elastically to more than double its original length before it breaks. When the hand is first jammed into a crack, like the one Mike was climbing, the skin will stretch and move, which can cause the hand to slip from the crack.

Tape on a hand does not stretch. It anchors the skin in place, making the climbing of jam cracks more secure. (The tape plays another important role as well. It connects the fingers to the wrist and acts like an external ligament, transmitting some of the force from the fingers to the wrist bones and easing the work of the internal ligaments and muscles.) As Mike moved higher, the crack narrowed down until his fist wouldn’t fit, so he switched to finger jams. Mike piled his fingers,
one on top of the other, inside the crack, keeping his elbow pointing straight down. When he raised his elbow, his fingers were twisted hard into the sides of the crack, where they stuck solidly by friction. Occasionally, he would stop and hang from one finger jam to place protection with the other hand. Before long, he had climbed fifteen storeys above me, and it was my turn to follow.

Following is fun. The rope runs straight up to Mike, who takes up the slack as I climb. Without worry, I could enjoy the pleasures of strong, precise, balanced movement. A climbing school in Colorado has captured the spirit of climbing perfectly in its name, “Dance in a Vertical World”. I even whistled a bit as I climbed. Whenever I reached one of Mike’s pieces of protection, I paused and removed it. We left nothing behind.

I joined Mike at the ledge just as the sun peeked over the top of the cliff, bathing us in warm light. I was having fun and was happy to take the lead again.

I knew that the rock ahead was easier – and that was probably why I ran into trouble at the ceiling. I worked my way up under the roof of rock and then reached out over the edge to find a “Thank God” hold for one hand and a small hold for the other. I had been moving up so well that I just launched my body out into space and began to do a pull-up. Hanging there, the pull of a few fingertips held me up against the gravitational pull of every atom of the earth. Somehow, it didn’t seem like a fair battle, and yet the fingers were winning – until one of my holds broke off.

I dropped suddenly to one hand, shock-loading it with my entire weight. Adrenaline started to work and I held on, reaching up to find a better hold with my free hand. I found a great hold, one I should have found before, but had missed in my haste. The adrenaline was still pumping, so I pulled over the roof on these good holds and kept climbing. I shook for a while at the next belay as the adrenaline wore off.

When we arrived at spacious Crescent Ledge, halfway up the climb, we savoured some fruit and cookies for lunch. Crescent Ledge is 2 m wide and long enough so that we could both stretch out like lizards in the sun. My hands enjoyed the rest. They were getting a little tired, and there was a long way to go.

The rest of the climb was pure joy. Cracks and faces full of solid square handholds let us almost run to the summit. We climbed in good style too: our hands were so tired from the earlier pitches that we had to use them as little as possible. Using hands for balance and transferring weight to the feet is the essence of good climbing.

Suddenly there was no more up. The world spread all around us. Granite domes smoothed by the last glacier protruded from the trees far below. They glowed orange in the light of the setting sun. I wanted to climb them all!

We walked down the back side of Fairview Dome. Some would say we were silly for not walking up the easy way in the first place. But where is the challenge in that? The summit was a reward to both of us, a reward for our efforts in climbing up 300 metres of rock that tested our abilities.

Back at camp, I looked at my hands. They were sore and abused. I had several cuts that I hadn’t noticed when I got them, but that I sure knew about now. Probably cuts from sharp crystals in a crack. I cleaned out the cuts and decided to take it easy tomorrow and let my hands heal. They deserved it. But then Mike said, “Hey, PD, that was great, but there’s a wonderful climb not far from here called West Crack…” I knew then that my hands would get no rest tomorrow.

Getting the feel of your hand
The legendary Sherlock Holmes could tell a great deal about a person by looking at his or her hands. The elementary explorations outlined here let you become a detective and learn how your hands are put together. You can use your eyes and the fingers of one hand to examine the construction of your other hand.

Each finger of your hand has a row of three bones, called phalanges, running down the centre; each thumb has two phalanges. You can easily feel the phalanges by squeezing the fingers of one hand between the index finger and thumb of your other hand. Your fingers bend at knuckle joints, where the phalanges are held together by ligaments, muscles and tendons. Different people can bend each joint different amounts. Compare the range of motion of your fingers with those of your friends. The finger joints are lined with cartilage. When cartilage is compressed by the motion of a finger, a very slippery fluid, called Synovial fluid, oozes out to lubricate the joint. Synovial fluid reduces the friction to almost nothing, which helps reduce wear and tear on joint surfaces as two adjacent phalanges slide against each other. Hold on to one finger phalange and feel how smoothly your knuckle joint bends.

The major muscles that power your fingers are in your forearm. Watch the underside of your forearm as you curl your flat hand into a fist. You can see the forearm change shape as the muscles contract.

Many smaller muscles are located in the hand itself. These small muscles position your fingers precisely so that the major muscles can then apply a larger force. The pad at the base of your thumb contains one such muscle. As you touch your thumb to the tip of your little finger, you can use the fingertips of your other hand to feel this muscle tighten.

A single long bone, called a metacarpal, connects each finger and thumb to a set of eight bones in the wrist called the carpal bones. By pressing on the back of one hand with the fingers of the other, you can trace these long, straight metacarpal bones back to where they join the lumpy bones of the wrist.

There are eight wrist bones, or carpal bones, which fit together like the pieces of a jigsaw puzzle. They are arranged in two rows of four bones, forming an arch. The tendons that deliver power from the under-the-forearm muscles run through the tunnel under this arch, called the carpal tunnel. A band of ligaments stretched across the bottom of the carpal tunnel holds the tendons prisoner.

In addition to the tendons, the carpal tunnel is packed with blood vessels and nerves. Make your hand into a fist again while you feel the bottom of your forearm just below the wrist. You should be able to feel tough, straight, cable-like tendons. Wiggle


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