'Harder, better, faster, stronger'-tethered soft exosuit reduces metabolic cost of running

May 31, 2017
A system of actuation wires attached to the back of the exosuit provides assistive force to the hip joint during running. Credit: The Wyss Institute at Harvard University

What if running the 26.2 miles of a marathon only felt like running 24.9 miles, or if you could improve your average running pace from 9:14 minutes/mile to 8:49 minutes/mile without weeks of training? Researchers at the Wyss Institute and John A. Paulson School of Engineering and Applied Sciences (SEAS) at Harvard University have demonstrated that a tethered soft exosuit can reduce the metabolic cost of running on a treadmill by 5.4% compared to not wearing the exosuit, bringing those dreams of high performance closer to reality. "Homo sapiens has evolved to become very good at distance running, but our results show that further improvements to this already extremely efficient system are possible," says corresponding author Philippe Malcolm, Ph.D., former Postdoctoral Research Fellow at the Wyss Institute and SEAS, and now Assistant Professor at the University of Nebraska, Omaha, where he continues to collaborate on this work. The study appears today in Science Robotics.

Running is a naturally more costly form of movement than walking, so any attempt to reduce its strain on the body must impose a minimal additional burden. The soft exosuit technology developed in the lab of Wyss Core Faculty member Conor Walsh, Ph.D., represents an ideal platform for assisted running, as its textile-based design is lightweight and moves with the body. A team of scientists in Walsh's lab led by Wyss Postdoctoral Fellow Giuk Lee, Ph.D. performed the study with an exosuit that incorporated flexible wires connecting apparel anchored to the back of the thigh and waist belt to an external actuation unit. As subjects ran on a treadmill wearing the exosuit, the actuation unit pulled on the wires, which acted as a second pair of hip extensor muscles applying force to the legs with each stride. The metabolic cost was measured by analyzing the subjects' oxygen consumption and carbon dioxide production while running.

The team tested two different "assistance profiles," or patterns of wire-pulling: one based on human biology that applied force starting at the point of maximum hip extension observed in normal running, and one based on a simulation of exoskeleton-assisted running from a group at Stanford University that applied force slightly later in the running stride and suggested that the optimal point to provide assistive force might not be the same as the biological norm. Confirming this suspicion, Lee and colleagues found that the simulation-based profile outperformed the biology-based profile in reducing metabolic cost by about a factor of two. As the authors note in the paper, "Our finding supports a paradigm shift toward the concept that mimicking our current understanding of biology is not necessarily always optimal."

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A tethered soft exosuit reduces the metabolic cost of running by 5% in a Wyss study funded by the DARPA Warrior Web program. Credit: The Wyss Institute at Harvard University

To clarify why applying force later in running stride improved metabolic expenditure so dramatically, the team analyzed what was happening to the subjects' other joints when their hip joints were being assisted by the actuating wires. They found that the simulation-based profile also affected knee extension and the forces between the foot and the ground, while the biology-based profile did not. "The biological profile only takes into account the amount of torque in the hip joint, but the human body is not a series of independently acting parts - it's full of muscles that act on multiple joints to coordinate movement," says Lee. "Applying force to the hip affects the whole body system, and we need to consider that in order to give the best assistance." While the study's results suggest that the increased biomechanical involvement of the simulation-based assistance profile is responsible for the reduction in metabolic cost, further biomechanical analyses are needed to confirm its findings.

A system of actuation wires attached to the back of the exosuit provides assistive force to the hip joint during running. Credit: The Wyss Institute at Harvard University

The team hopes to continue this research to reduce the metabolic cost of running even more. "We only tested two actuation profiles in this study, so it will be interesting to see how much more the cost of running can be reduced with further optimization of the system," says Malcolm. "Our goal is to develop a portable system with a high power-to-weight ratio so that the benefit of using the suit greatly offsets the cost of wearing it. We believe this technology could augment the performance of recreational athletes and/or help with recovery after injury," adds Lee. The days of a battery-powered exosuit for high-performance runners are still beyond the horizon, as the actuator unit (including motors, electronics, and power supply) in this study was off-board, but the authors say technology is moving toward making an untethered assistive possible in the near future. "This study is a great example of how our team can quickly leverage its experience and expertise in wearable technology and biomechanics to demonstrate how human performance can be improved in new application areas," says Walsh.

"Our work at the Wyss is biologically inspired and, as shown by Conor's team's advance, sometimes we learn that a conventional biological view of a mechanism is not really how living systems work; we need to place individual components - in this case, a human hip joint - in context of the living whole. When we do this right, transformative new technologies emerge," says the Wyss' Founding Director Donald Ingber, M.D., Ph.D., the Judah Folkman Professor of Vascular Biology at Harvard Medical School (HMS) and the Vascular Biology Program at Boston Children's Hospital, as well as Professor of Bioengineering at Harvard's School of Engineering and Applied Sciences (SEAS). "Studies like this are also a great example of the power of thinking beyond the limitations that Nature has handed us and asking, 'Can we do better?'"

Explore further: Significant metabolic energy savings gained from wearable, gait-improving robot

More information: G. Lee el al., "Reducing the metabolic cost of running with a tethered soft exosuit," Science Robotics (2017). robotics.sciencemag.org/lookup … /scirobotics.aan6708

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EmceeSquared
3.7 / 5 (3) May 31, 2017
To be clear, this study does not offer any exercise benefit, despite the anonymous author's stupid lede. Running more treadmill miles is of no benefit to a tethered runner if it exerts *less*; the only point of exercise is the exertion.

But the study offers an important scientific insight: "Our finding supports a paradigm shift toward the concept that mimicking our current understanding of biology is not necessarily always optimal" , as the article quotes the paper's two (named) authors. This indicates that while biomimickry can find efficiencies evolved by nature, those efficiencies aren't necessarily optimal.

Of course, running a treadmill isn't the complete selection criteria that evolved human running. Further study might find other factors in human reproduction (including, but not limited to, survival) at odds with the tethered suit's more metabolically efficient running. For example, it might be harder to find a date tethered in a running suit.
PPihkala
not rated yet Jun 01, 2017
Of course, running a treadmill isn't the complete selection criteria that evolved human running. Further study might find other factors in human reproduction (including, but not limited to, survival) at odds with the tethered suit's more metabolically efficient running. For example, it might be harder to find a date tethered in a running suit.

Because the system is not portable, they have to keep the runner stationary, therefore the treadmill. Probably these kind of assistive systems when ready with clear gains will first be used with soldiers.
EmceeSquared
1 / 5 (1) Jun 01, 2017
PPhikala:
Because


For a 1% improvement to optimal, at cost of complexity, I don't think so. The value here is the scientific proof that millions of years of human evolution haven't optimized running to perfect metabolic efficiency. With its implications for biomimickry's efficiency. As the scientist quoted in the article said.
antialias_physorg
5 / 5 (2) Jun 01, 2017
The value here is the scientific proof that millions of years of human evolution haven't optimized running to perfect metabolic efficiency

I think no one has ever claimed that evolution produces something perfectly optimal (which in any case it can't because what is optimal is a function of environment, which includes the effects on the environment of an adapted organism. So even in a fully static external world - which we don't have - 'perfect' is a moving target).

It's probably easiest to see this from the POV of evolutionary pressure (i.e. selection criteria). There is no pressure to be optimal. There is only ever a pressure to be better than whoever you're incompetition with (which can be members of other species but also members of your own species)

Just like the joke goes: "I don't have to be able to run faster than the bear. I just have to be able to run faster than you. "
antialias_physorg
5 / 5 (1) Jun 01, 2017
Just wanting to add: To define optimality by only one criterium (e.g. walking efficiency) seems like a narrow view. Organisms have many things they want to optimise. Some of which are:

- Energy expenditure (which would fall within the optimality criterium in the article)

- Breeding success (imagine if a more efficient running structure were to result in an 'ugly' configuration that does not allow for finding a mate?)

- Robustness of the genetic code (imagine if a more efficient running structure requires a lot more finnicky genetic sequences to be expressed within a very specific time sequence. Chance of failure - resulting in disability or death of the organism - might skyrocket)

- impact on internal organ function not related to running from a changed structural makeup (Less space for intestines? Liver?)

- ...

Organism are complex. Defining what 'optimality' is is an ambiguous proposition, at best.
EmceeSquared
3 / 5 (2) Jun 01, 2017
antialias_physorg:
I think


Well, biomimickry and other design guided by biology does value selected biological performance highly. Abstract "genetic algorithms" in computing aim to find the best solution fit to the criteria by evolving.

I don't know if this exosuit research challenges a claim of "perfectly optimized", but it does establish a margin beyond the natural achievement, at least against the metabolic efficiency criterion. In fact, since the natural is within 1% of this synthetic max, metabolic efficiency seems the overwhelming driver vs other compromising criteria pressure.

In short, the project's showing evolved human running is extremely efficient metabolically, but not perfectly so, tells us about both human evolutionary pressures and the efficacy of our adopting evolution for engineering.

PS: "criterion" :).
antialias_physorg
not rated yet Jun 01, 2017
In short, the project's showing evolved human running is extremely efficient metabolically, but not perfectly so

Yes. I'd also expect some natural variability due to everyone being a bit different. If we were all perfect in that regard despite natural variability then it would actually be an argument for a 'designer'.

Abstract "genetic algorithms" in computing aim to find the best solution fit

Genetic algorithms are very powerful tools. That said they do not (and cannot) guarantee optimality of the solution (for the same reason as natural evolution. If the search space does not provide strong gradients or is highly irregular the chances of getting stuck in local optima is large)

PS: "criterion" :).

Lol...thanks. Screwed up a translation there ("Kriterium" in german). Wasn't aware of the cycling meaning of criterium in english.

You live and you learn...at any rate: you live.

EmceeSquared
1 / 5 (1) Jun 01, 2017
antialias_physorg:
Yes.


At any rate we go round and round the track, whether or not we get it right :).

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