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Saturday, February 24, 2024

Astronaut Gear of the Future May Fight Bone and Muscle Loss

On Monday, an astronaut capsule that looks like a giant orange juicer splashed down in the Atlantic Ocean, bringing its four-person crew back under the influence of Earth's gravity. These astronauts have spent six months on the International Space Station, and so the gravity now tugging at their bodies will feel familiar to them, but strange.

This team, called SpaceX Crew-2, spent much of the past half-year in orbit doing spacefaring scientific work, like testing out “tissue chips,” small-scale analogs of human organs. But they also whiled away the hours as gym rats: Six days a week, they had a 2.5-hour exercise block to reduce the damage that living in space can do to the body. Space, as they say, is hard. But it’s particularly hard on humans. Radiation, lack of gravity, and living in confined spaces each take their tolls.

“NASA has always been concerned with the effects of spaceflight on the human body, from the very first space missions,” says Michael Stenger, element scientist for Human Health Countermeasures, the agency’s arm dedicated to understanding how spaceflight affects physiology and mitigating those effects. One big problem is that living on-orbit is physiologically similar to bedrest, even if you’re bouncing around doing experiments all day. “Being in space is a lot like laying around doing nothing,” he says.

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When you don’t need to counteract gravity, your muscles and bones lose strength, because those parts of the anatomy adhere to a sort of “use it or lose it” philosophy. Muscles can atrophy, the same way they would if an astronaut laid on the couch playing Fallout all day. Bones can lose mass: They both form and break down based on the forces they experience day to day, from both gravity and muscle use. After six months in space, the proximal femoral bone in the leg can ditch around 10 percent of its mass, requiring years of recovery back on the ground.

Space is also hard on the cardiovascular system, says Stenger: “Your heart no longer has to pump as hard to maintain blood pressure, so your heart becomes weaker.” During astronaut Scott Kelly’s year in space, his heart shrank in size by more than a quarter, adapting to fit its new conditions. Back under the influence of gravity, the heart can pump itself back up to normal, seemingly without long-term damage.

Scientists don’t fully understand why, but astronauts’ spines also grow longer in space, and they gain a few inches of height. The travelers shrink back to their normal sizes on Earth, but after flight, astronauts have a higher risk of disk herniation, which may be associated with these spinal shifts. Also, their suits and equipment have to be designed for their dimensions—and if those dimensions are changing, the design gets complicated, especially for a longer trip.

To keep astronauts’ innards fit for their tasks in space and healthy once they’re back on Earth, Human Health Countermeasures has tried to right these physiology wrongs—in part with gym gear built for space. The Advanced Resistive Exercise Device is a sort of space-based Bowflex: It uses vacuum cylinders to create a few hundred pounds of resistance, and microgravity athletes can reconfigure it to do deadlifts, squats, or bench presses for two hours, including the time it takes to reconfigure the device and do a little recovery. The ISS is also kitted out with a treadmill and a cycling machine, which the astronauts use for 30 minutes of interval training.

That sort of luxe setup won’t always be possible, though, on future missions to the moon and eventually Mars. “We're sort of in the sweet spot where we have this beautiful floating laboratory and space with all kinds of room to do all the kinds of measures that we want to,” says Stenger, “and all of the future programs are going to be in tiny little vehicles.” Flights to these destinations will be longer, leaving more time for ill effects to develop. And on top of that, future astronauts will need more oomph for more—and more difficult—extravehicular physical activity than today’s explorers do, to stay alive and functional on another world.

So if space workouts won’t be enough, maybe future astronauts need different gear. Two students at MIT, both Draper Scholars at Draper Laboratory, a nonprofit engineering company that often does work for NASA and the Department of Defense, are now working on possible solutions to counteract muscle and bone problems. One is a sort of auto-exercise device that can contract muscles like movement would, and the other is a skintight space suit that simulates the effect of gravity.

“We need to make sure they're as healthy as possible,” says Thomas Abitante, the Draper Scholar working on the muscle-toning device. “But we can't really add more exercise. So what else can we add?”

Abitante and his Draper Scholar colleague Rachel Bellisle are both PhD candidates at MIT’s Human Systems Lab, part of the university’s aeronautics and astronautics department. Draper Lab pays their doctoral tuition and stipends, and the students do their thesis research co-supervised by a university faculty member and a Draper technical staff member. This school year, there are 55 Draper Scholars at 11 universities.

Bellisle’s research involves helping design a skintight space suit officially called the Gravity Loading Countermeasure Skinsuit—or just “the Skinsuit,” in conversation—that could compress the body enough to simulate some of gravity’s effects, help keep the spine from elongating, and keep the “antigravity” muscles that humans use to maintain posture and move—like the quadriceps and muscles in the back—from atrophying and causing motor-control deficits, like trouble with balance and coordination once astronauts return to gravity. “When we go into reduced gravity or space, those muscles aren't needed as much,” says Bellisle, who has been at MIT since 2018.

Bellisle is working with Caroline Bjune, a principal member of the technical staff in Draper’s mechanical design and system packaging division, and astronautics professor Dava Newman at MIT, whose lab developed the first iteration of the Skinsuit about a decade ago. It compresses the whole body at once, from the shoulders to the feet. This version of the suit is made of Primeflex—a super-stretchy elastic material made of polyethylene terephthalate and polytrimethylene terephthalate. It compresses in two directions, laterally and vertically. The load from that squeeze simulates some of the effects of gravity, and makes the body behave more like it would on Earth. The eighth iteration of the suit will likely use a different fabric.

Astronauts tested a version of the suit on the Space Station between 2015 and 2017, and today, Bellisle is working on its seventh iteration, the Mk-7, investigating how to make the next version more comfortable and minimize musculoskeletal changes induced by the space environment. The shoulders and foot stirrups could be more comfy, she found. “I'm also identifying parts of the suit that should be changed to better target the muscles we are interested in,” Bellisle says.

Comfort is important—the form and the function have to be right. Bellisle recalls a “body-loading” garment Russian cosmonauts wore called the Penguin suit. “Essentially, it was a suit with a bunch of bungee cords,” Bellisle says. The cords could stretch from a belt to the shoulders, and from a belt to the feet, or just from the shoulders to the feet, providing a “load” on the body not unlike gravity’s. The problem? The cosmonauts would cut the bungee cords once no one on Earth could stop them.

The Skinsuit is designed to put more consistent loads on the body, making it more effective. The new suit has gotten pilot testing in Earth gravity, in a partial-gravity simulator, and on parabolic flights that induce microgravity. Bellisle’s team has stuck electrodes on the test-user’s body to measure their muscles’ electrical impulses, an indicator of how active they are. Bellisle is currently working on comparing the muscles’ activity levels in different gravitational environments—typically highest in Earth-like 1g, where muscles were meant to live—to see if the suit’s squeeze can help induce normal activity levels in lower gravity, and determine whether the muscles’ coordination patterns differ in lower gravity compared to on the ground.

But there’s a drawback: These pilot studies have only been done on one person. The team’s results—to be published in the spring—have to be vetted and replicated, and tried out on a larger sample size.

Abitante, who studied astronautical engineering as an undergrad before signing on for graduate school at MIT in 2017, grew up reading novels about human derring-do in the great beyond. But in college, he noticed a big disconnect between the robotics and satellite projects he saw around him, and the human-centric exploration in books. ‘Where's the path towards the future of everything you see in sci-fi?’” he asks. That’s part of why he’s pursuing a pretty sci-fi idea of his own: He hopes to build a wearable device that would let astronauts zap their muscles to simulate the effects of exercise. At Draper, he’s supervised by Kevin Duda, group lead for space and mission critical systems.

This idea is already used in treatments for spinal cord injury patients. Electrical stimulation—specifically, a kind called neuromuscular stimulation—can cause muscles to contract, even if the brain isn’t telling them to. These stimulations can fire, say, the quad, hamstring, and glute in sequence, allowing patients who can’t otherwise control their limbs to do things like pedal a bike. In the past 10 years, researchers have investigated whether similar technology could help those in wheelchairs maintain bone mass—helpful because falls from a wheelchair can result in broken hips. Research suggests that stimulating muscles, which then put force on bones and deform them slightly, encourages those bones to stay strong. “So it was a hop, skip, and jump for me to be like, ‘Who else has disuse-associated bone loss?’” says Abitante. “Astronauts.”

His ideal cosmic zapping device would attach to an astronaut’s belt, and he envisions it stimulating their muscles periodically throughout the day. But before he can build a space-centric prototype, he has to learn how much force electrically induced contractions actually put on bones—and how effective it might be in shoring up their strength. “There's a lot we don't know about how bone responds,” he says. Most models come from experiments on rodents and birds, with that data extrapolated to suit human anatomy. “We can still infer human bone behavior based on the animal experiment,” he says. “This work is useful because the strain from electrical stimulation can be used to infer its effectiveness as a bone-loss tool both in space and on Earth.”

Now he’s doing his own research with people, like semiprofessional athletes he coaxed into cooperation by doing outreach at local gyms, and running or weightlifting clubs. He zaps study participants’ muscles with electricity, and uses biomechanical modeling to estimate how much strain is exerted on their bones. Then he compares that force to what’s generated by other activities, like walking or resistance exercise, to see if the synthetic version can measure up.

He’s also testing out how long it takes for their muscles to get tired, because he wants to know how long the contractions from a single simulation period will be effective, and whether the device can deliver enough in a day to make a difference.

So far the results—yet to be published, although they’ve been preliminarily presented at a recent meeting of the International Society of Biomechanics—are variable. “It really depends on the individual, how strong their contractions are,” Abitante says. Athletes who did activities like judo or powerlifting had stronger device-created contractions, which in turn put more pressure on their bones. “Your body is the exercise machine,” Abitante says.

The students’ two projects have complementary flavors. Bellisle’s suit would be a kind of base: a steady and constant part of an astronaut’s body maintenance. “I'm increasing a little spice throughout the day,” says Abitante.

Their work is still preliminary, but the ideas they are exploring could be useful on our own planet, not just for the astronauts of the future. “I definitely love thinking about the Earth applications,” says Bellisle. Better compression garments could help those with lymphedema, a condition that leads to fluid buildup in the soft tissue, by reducing swelling and redistributing fluid. Knowing more about how muscle stimulators work could help improve treatment for bedridden patients, paralyzed people, and those who use wheelchairs.

Those applications are important—both for their own merits, but also because no one actually knows for sure when (or if) astronauts will fly long-term missions. Still, Abitante feels the pull of that future. “I, personally, have no intention to go to Mars,” he says. “But that doesn't mean I don't want to help make sure I see it on the news one day.”

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