The problem with rigid frames
Early powered exoskeletons were rigid structures of metal and motors that ran alongside the wearer’s bones. They could carry loads and support weight, but they were heavy, took time to fit and often forced the body’s joints into positions that were not quite natural. A frame whose joints do not line up exactly with the wearer’s joints can cause discomfort or even resist movement. Designers began asking whether a device that only added a modest push at the right moment might be enough for some purposes, and far lighter.
That question is the starting point of the soft exosuit. The term describes a garment-like system: fabric worn on the body, anchored at points such as the waist, thigh and calf, with cables or other actuators that pull along paths similar to muscles and tendons. Sensors detect the wearer’s movement, and a controller times the assistance accordingly.
No single moment of discovery
It is hard to name a single discoverer. Wearable aids built from elastic bands and cables were tried by various groups, and the idea that clothing could assist movement appeared in different forms in several research programs. Efforts that are often mentioned include work at SRI International on “powered clothing” and the university programs described below. The shared idea was gradual: replace the skeleton-like frame with the wearer’s own skeleton, and let the body carry the load.
DARPA’s Warrior Web
A major boost came from the U.S. Defense Advanced Research Projects Agency, which had already funded heavier military exoskeletons that were meant to add strength. Around 2011 it announced a program called Warrior Web, which asked for lightweight, under-clothing systems that could reduce soldiers’ injuries and fatigue when carrying heavy loads over long distances. The program funded several teams, including one led by Harvard University researchers working with the Wyss Institute. Among the names often associated with the Harvard work are Conor Walsh, an engineer focused on wearable robots, and Robert Wood, known for soft and small robotics, together with collaborators in biomechanics.
The Harvard team built suits of textile anchors and Bowden cables, the same type of sheathed cable used for bicycle brakes, driven by small motors carried on a belt or backpack. By pulling at the ankle as the wearer pushes off the ground, the suit added a small amount of force. In published laboratory studies in the middle of the 2010s, teams reported small reductions in the energy walkers used on a treadmill. These were measured on healthy adult volunteers under test conditions, and results differ with walking speed, load and individual. That is a reminder that gains in the laboratory do not always carry over to real terrain.
From laboratory to clinic
Researchers soon turned to medical uses. People recovering from stroke often walk with an asymmetrical gait, and a light suit that assists the weaker leg at the right point in the stride seemed a promising kind of therapy. The Harvard group and its partners conducted studies with stroke patients, and a version of the technology was developed commercially for walking rehabilitation. A device based on it received clearance from the U.S. Food and Drug Administration for use in stroke rehabilitation around 2019. Such devices are used under the supervision of clinicians, and this article covers history only.
Other groups explored suits for different needs, including assistance for lifting and bending, support for the hips of older adults, and wearable aids for people with muscular conditions. Early evidence from small studies is encouraging in some cases and mixed in others, so it is wise to treat claims about benefits with caution.
How soft suits differ from rigid ones
The main advantages of a soft suit are weight, comfort and freedom of movement. The wearer can move naturally and can usually walk, sit and bend with the suit on, and it is not limited to a few joints. The disadvantages follow from the same design. Fabric stretches and shifts against the body, so forces are harder to deliver precisely. Cables can only pull, not push, and a soft suit does not carry the body’s weight the way a rigid frame does. Anyone who needs full support, as in paralysis, is likely to need a rigid device.
Power and control remain engineering challenges. The motors, batteries and sensors must be small enough to wear comfortably, and the control software has to recognize each wearer’s gait quickly. Progress in compact electric motors and better sensors, much of it from outside the field, has helped. Some designs now use inflatable fabric actuators or electrically driven fibers, which connects to wider research in soft robotics and artificial muscles.
Legacy
The soft exosuit shows how a field can progress by reversing a design assumption. Early engineers assumed a machine had to be stronger than the body to help it. Later researchers found that a small, well-timed contribution could be useful, and that comfort and simplicity mattered as much as raw power. How widely such garments will be used, and for what, is still being worked out.