This exomuscle gives autonomy to people with reduced mobility

You are probably familiar with exoskeletons, but exomuscles seem even more interesting from a medical and orthopedic point of view.

Even if they are often very different from those we are used to seeing in fiction, exoskeletons are already a reality. Some manufacturers have chosen to equip certain workers or handlers with these external mechanical fittings; they make it possible, among other things, to lift heavy loads with very little effort, which greatly reduces the difficulty of the work and the risk of injury.

But what is less obvious for part of the public is that they are also gradually colonizing the medical environment. Many laboratories and other institutions are indeed working to develop revolutionary exoskeletons that could, for example, allow a paraplegic person to walk again.

But as it stands, these projects remain in their infancy; we are still relatively far from reaching a stage where these exoskeletons are in the process of being democratized. And for good reason: most of them are heavy and bulky, and still fail to align perfectly with human joints. This forces the wearer to perform unnatural movements, which can result in injury. And above all, this often results in additional energy expenditure which considerably limits the interest of this technology.

An artificial muscle that is worn like a garment

In recent years, many researchers have therefore explored lots of new avenues to design high-performance machines, but significantly lighter, and above all capable of conforming to the anatomy of the wearer. And that is precisely what the engineers of the prestigious ETH in Zurich are trying to do with their Myoshirt.

Here, the approach is very different. Instead of relying on a rigid frame like in a classic exoskeleton, researchers have developed a garment that behaves like a set of muscles and tendons. This garment is composed of a kind of vest and an armband. Both are traversed by a cable whose length is managed by a small motor. They are also lined with sensors such as accelerometers which allow the movement of the wearer to be analyzed in real time.

When the sensors detect the start of a movement, they first analyze its trajectory for a fraction of a second. From these few snippets of information, the system is able to guess the movement desired by the user. He can then precisely calculate the force necessary to achieve it. At this stage, the engine takes over. It allows the cables that run through this exomuscle to be stretched, exactly like a tendon, to accompany and facilitate movement.

A more “organic” approach to the exoskeleton

The advantage of this predictive system is that it is possible to adapt precisely to the movements of the wearer so that he reacts exactly as expected. The user therefore does not benefit from exceptional strength as with a standard exoskeleton. On the other hand, he remains entirely in control of his movements.

The researchers tested their prototype on a dozen participants. Ten of them were healthy. The other two suffered from serious illnesses that severely handicap their mobility. In this case, it was respectively a myopathy (a neuromuscular disease that weakens the muscles to the point of tearing) and a serious injury to the spinal cord.

© ETH Zurich

The researchers asked each subject to raise their arm for as long as possible in order to estimate the gain in endurance provided by the Myoshirt. And the preliminary results have been very encouraging, regardless of the patient’s condition.

In healthy subjects, the researchers observed an average endurance gain of around 30%. The patient with myopathy, on the other hand, managed to keep his arm raised twice as long. And the spectacular result is probably that of the last volunteer with his spinal cord injury; he simply tripled his score!

An obvious interest for people with reduced mobility

In the end, the result is final. This exomuscle made it possible to considerably limit the muscular constraints. This is life-changing for many individuals whose mobility has been reduced, especially in cases involving neurological problems.

Let’s take the example of a person suffering from a disease like Parkinson’s, or who has developed motor problems following an event like a stroke. In these cases, the subtle neurological dynamics that serve to perform routine actions, such as walking, can be completely out of whack. In addition to the obvious problems that this generates on a daily basis, these situations are also physically exhausting for the patients concerned. Indeed, the human body has evolved to save as much energy as possible when performing routine actions such as walking.

© ETH Zurich

When you take a step, not all your muscles are constantly mobilized to propel the body. Walking is essentially a long, very controlled fall forward. Muscles aren’t just for propulsion; one of their most important roles is to maintain balance while gravity and inertia do the rest. But when the nervous system is damaged, this very fine dynamic can stop working. Patients must therefore compensate with other less natural movements. And these movements tend to be extremely energy-intensive compared to normal walking, which is very efficient.

In these cases, prostheses of this kind could slightly correct the posture. But above all, they would allow you to move freely without spending crazy energy to perform a few simple gestures. The Myoshirt in particular is limited to the upper limbs, but overall the idea is applicable everywhere. Suffice to say that it could be a real blessing in terms of autonomy for all people who suffer from mobility disorders.

The size and weight of the motor and the battery further limit the practical interest of this technology… for now. © ETH Zurich

We will still have to wait before we get there. As it stands, this technology is not yet ready to be used in real conditions. This is largely down to the weight of the motor and battery; alone, they currently weigh 4kg. A figure still far too high for an application of this type.

But when one scans this work and that of other institutions, such as the prestigious Wyss Institute at Harvard, which has developed a comparable system for the legs, there does not seem to be the slightest doubt as to the viability of the concept. All that remains is to miniaturize the whole thing, then to develop a real commercial product.

The text of the study is available here.

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