Inventing Iron Man (7 page)

If you can appreciate the mechanics of walking in this way, it becomes pretty clear why there has been so much controversy over a device that changes the properties of the legs. Essentially the “blade runner” prosthetic used by Oscar Pistorius dramatically increases that springiness. It stands to reason that this would also make performance much better. However it was mostly an intellectual argument until recently.

Because of all the legal issues that arose from the track and field controversy, it was necessary to see if there was any science behind the contentions. Several movement scientists were called in to measure the physiological cost of walking and running and the bio-mechanics of using prosthetics. Peter Weyand and colleagues performed studies comparing the speeds, metabolic energy cost, and biomechanical characteristics of the double amputee running with the blades with those of elite, high performance track athletes. Incredibly, the use of the blades allowed for almost equivalent performance to elite level runners. This is stunning in terms of how technological advance in prosthetics can give rise to such a leveling of the playing field. However, it has raised some additional concerns about whether the use of such technology may actually allow for increased performance, that is, for performance better than that of people with intact limbs.

Figure 2.7. The circle represents the body center of mass suspended over the legs, which work as springs while walking (
A
); the “leg spring” comes from controlling muscles that cross the hip, knee, and ankle (
B
); exoskeleton worn over the leg used to change the mechanical responses of the ankle joint (
C
). Courtesy Daniel P. Ferris.

Figure 2.8. Parade performer in Disneyland, California, using a lower limb exoskeleton to amplify the springlike activity that the legs produce normally.

The bottom line of all the scientific analysis is that the carbon fiber “blades” could significantly enhance performance. This is largely
because the blades allow for a far more efficient running pattern. The blades are actually much lighter than the lower legs they replace, which means that the legs can be moved about 15% faster than the highest performance of sprinters with intact legs—including 2008 double gold medal winner Usain Bolt of Jamaica. Also, the same overground running speeds could be obtained using the blades while applying about 20% less force into the ground. Overall the “springiness” of the blades meant that only about one-half of the muscle force needed for sprinting at the same speeds with intact limbs was needed with the prosthetic legs.

If Oscar were a marathon runner, there would be different issues. On New Year's Day in 2010 American ultradistance runner Amy Palmiero-Winters won the “run to the future.” She covered 130.4 miles in 24 hours, making her the first person with a prosthetic lower leg to qualify for the U.S. track team. Her situation is different from Pistorius, because the mechanical benefits Amy might get from a single prosthetic leg don't really help with long-distance running.

If you keep your eyes open, you can see small-scale applications of assisting human movement with technology in many different places. I took the picture of a performer during a family trip to Disneyland in 2009 (
figure 2.8
). The basic ideas we have been discussing are clearly shown in how he used spring boot pogo sticks to amplify movement. The main point of this as it relates to Iron Man is that even simple devices can augment and improve function in people with amputation—and those like the Disneyland performer who are just trying to have fun.

What is important to consider is that really efficient machine-based locomotion should probably mimic what we do when we just walk around. So, an Iron Man armored suit should do the same. After all, as Tony Stark said while testifying at the “Weaponized Suit Defense Program Hearings” (shown in the
Iron Man 2
movie), his device is really just “a high-tech prosthetic.” Now let's look at some other prosthetics that link directly to the nervous system.

CAN WE CONNECT THE CRANIUM TO A COMPUTER?

Undergoing the Extremis Procedure remade my body from the inside out. Long story short, my body was turned into a kind of computer designed to interface with the Iron Man. There was no longer a division between me and the suit. My brain … evolved, I guess. Into a kind of hard drive.

—Tony Stark, “World's Most Wanted,
Part 2
: Godspeed” (Invincible Iron Man #9, 2009)

The original version of the Iron Man armor was designed to preserve my damaged heart. The obvious next step was to extend the suit's preservative capabilities to an even more critical organ…. Not so much my brain per se, as my cognitive neurofunctions and basal personality structure.

—Tony Stark speaking out loud about new changes to the armor, from “Hypervelocity #2” (Iron Man, 2007)

Coffee pot on!” Imagine if you could, upon awakening, simply have that thought and your coffee maker would go on in your kitchen.
Or your kettle, if you prefer tea. Imagine if your thoughts could be transformed into the actions of machines. In the last chapter, we looked at muscles and how they make us move after receiving electrical commands from the nervous system. In this chapter, we look at how we can tap into the command signal from the nervous system to not just make muscles contract but to trigger powerful motors to move robotic suits of armor. Another focus of this chapter is on what happens when that chain of command is broken, which relates to that imaginary ability to turn on your coffee maker with thoughts alone. We will discuss how that works by giving some examples of prosthetic arms and legs being powered with the mind.

These real-life bionic men and women bring us to the fascinating field of neuroprosthetics. This term refers to devices that are used by or implanted into a person to improve sensory, and, in some cases, cognitive abilities, including retinal and cochlear implants to augment sight and hearing, spinal implants to relieve pain among other things, and implants to assist with bladder control. Something that Tony Stark would be able to use would be the implants that are being developed to control movement of an object by simply thinking about it. These inventions are in their infancy but are expected to help paraplegics and quadriplegics and others with severely limited movement. And who knows what else they might soon be able to do?

Some of the possibilities of the future are being revealed by pioneers such as Kevin Warwick, a professor of Cybernetics at University of Reading in the United Kingdom. Warwick is known for many things including “Project Cyborg”—his attempt to have implants placed into his body that can be used to control other devices. One of his early efforts was to have a computer chip implanted that could be detected by sensors outside his body to then turn on lights or other appliances. Later, he had an electrode array implanted in his arm. This array took information from a nerve in his forearm, which was used to control a robot arm “directly” and eventually over Internet relays. Warwick summarizes his approach in his book
I, Cyborg
. He has had some exciting successes with this approach, but the problems that have arisen in doing more complex tasks for longer periods highlights how difficult interfacing humans and machines actually is.

Remember from
chapter 2
that when you want to do something, you must activate your muscles. When you integrate your body with a robotic machine, you must skip the muscles and go directly from the output in the spinal cord straight on to the machine. In a way, we
are doing some wire-tapping in the nervous system. The first wire tap we want to set is from the spinal nerves. Later, we will also talk more about even tapping into commands from the brain itself using a special kind of neuroprosthetic—a brain-machine interface.

The general principles for neuroprosthetics, as well as other types of prosthetics, are similar for both amplifying human performance and for replacing it. Many advances in prosthetics have improved the “usability” and the look of the devices. As we saw last chapter, however, the limbs themselves don't actually function in the same way as in an intact situation. An idea that arose early on in the field of neuroprosthetics was controlling a motorized limb using commands from the nervous system. In other words, tapping into the commands that would normally activate the muscles themselves. Instead of needing to figure out exactly what the complex sets of commands should be for a given movement, a simple and elegant approach is to instead just use the input itself.

Most neuroprosthetics detect signals from the person's nervous system and relay these signals to an electrical controller inside the device. The biological signals could be electrical activity of muscle detected from electrodes on the skin or implanted in muscle, nerve signals detected by implanted electrodes, or even electrode arrays in the nervous system that have the nerve cells growing through them. In this way the controller of the neuroprosthetic is literally connected to the neuromuscular system and to the device. The commands from the person can then be detected and relayed to the device to make it do whatever it is supposed to do to replace the lost function.

If damage to the nervous system, such as an injury to the spinal cord, occurs, electrical stimulation can make the muscles contract even when the nervous system itself cannot provide the command for the contraction. Since the point of the stimulation is to help with functional movement, a term that arose is “functional electrical stimulation,” or FES. FES is now more broadly used to refer to using electrical currents to produce or suppress activity in the nervous system. When similar stimulation concepts are used to more generally alter activity within the nervous system, it is often called “therapeutic electrical stimulation.”

An example of a really useful FES device is the “WalkAide.” I bet you would never guess it helps with walking. The WalkAide is a small battery-powered device used to stimulate a nerve that activates the muscles that help flex your ankle to bring the top of your foot up when you walk. If your nervous system is working well, you probably pay this no attention at all, but the clearance of your foot over the ground when you walk is a hugely important issue during walking.

Because it is energy inefficient to pick the foot way up off the ground while walking, your nervous system activates your leg muscles so that the bottom of your foot just clears the ground by less than an inch. This is all fine and good until something like a spinal cord injury or a stroke occurs. These disorders lead to weakness of the muscles, particularly those that flex the ankle, and suddenly walking is much more difficult. You may have experienced a brief example of the outcome of this phenomenon, called “foot drop” or “drop foot.” Sometimes a piece of sidewalk will be broken and jutting up higher than the clearance of your foot while walking. You don't see it as a major object visually but then you scuff your foot and may trip. Well, after a stroke this is common even when the place a person walks on is level and smooth. Two simple things can be done: one is to swing the leg out and around when walking (so the affected leg arcs to the outside and forward—called “hip hiking”). The other is to wear an external brace of metal, plastic, or graphite that holds the foot at about a right angle so it cannot scrape against the ground. Neither is really a great approach. So where does FES fit in?

With the WalkAide (
figure 3.1
), based on the acceleration and the angle of the leg, a sensor detects the correct time during walking when flexing the ankle should occur but doesn't because the nervous commands are lacking due to injury. So, the WalkAide applies electrical stimulation to the nerve, activating the muscles that flex the ankle and allowing the person to pick up the foot. If you reach down the outside of your knee, you will come to a little bump on the outside of your lower leg just below the knee. This little bump is actually the “head” of the fibula—the leg bones we talked about earlier with Oscar Pistorius. Right near the head of the fibula is the common peroneal nerve that innervates the major flexor of the ankle, the tibialis anterior muscle (see
figure 2.1
). The WalkAide appropriately stimulates (and just as importantly) stops stimulating this nerve in order to get the foot moving better during walking. It is small, easy to use, and requires 1.5 volt AA batteries. The stimulator unit is shown
in panel A and a drawing of how it would help move the ankle by stimulating the ankle flexor muscles is shown in panel B. The bulk of the initial WalkAide technology was developed in the laboratory of Richard Stein at the University of Alberta in Edmonton, Canada, during the late 1980s and early 1990s. I was doing my doctoral training in neuroscience there in the 1990s and got to see some of the early prototypes from this work up close. It was captivating then and still is now. But back then it was an idea in development. Now it is an actual product that people can get and use to help improve their walking.