While weightlessness is often seen as the most captivating aspect of space travel, it also presents significant health risks. In a zero-gravity environment, astronauts experience muscle atrophy, changes in heart rate, elevated blood pressure, and bone deterioration with each month spent in space. For those on missions lasting a year or more, this poses a substantial threat of long-term damage. Although exercise helps—astronauts on the International Space Station (ISS) are mandated two hours daily on a treadmill and stationary bike—it proves insufficient to fully counteract these issues. Furthermore, hazards aren’t limited to zero-g; prolonged exposure to the reduced gravity of the Moon or Mars could lead to comparable adverse effects.

Retired astronaut Kate Rubins, who completed two ISS tours totaling 300 days in space, recounted her post-flight experience: “When I landed from space I had to be carried out of the capsule and went about my first few days on Earth looking like a 90-year-old.” She added, “Many of my physiologic systems replicated somebody who’s 20 or 30 years older than me.”

A potential solution has now emerged in the form of robotic pants. As reported in *Advanced Science*, a research team headed by Emanuele Pulvirenti, a research associate at the University of Bristol’s Soft Robotics Lab in the U.K., has engineered a garment. Designed to be worn beneath spacesuits, this apparel provides resistance similar to that experienced in a gravitational environment, thereby helping the body function as if still on Earth.

These waist-to-knee pants comprise two layers: an outer nylon layer and an inner, airtight plastic one. Positioned at the front and back of both knees are components known as Bi-directional Actuatable Modules (BAMs), constructed from plastic tubing and retaining rings. These BAMs can be air-inflated to apply pressure to the underlying muscles. Historically, BAMs have been utilized to support wearers’ muscles, aiding soldiers with heavy packs or individuals with disabilities in regaining mobility. However, for this study, Pulvirenti and his colleagues strategically placed these units to slightly increase the effort required for movement, promoting continuous, low-level exertion that mimics some health benefits of gravity.

To evaluate the system, Pulvirenti’s team journeyed to the University of Milan, home to the European Space Agency’s L.O.O.P. (Locomotion and Outer-space Orientation Platform) lab. The L.O.O.P. facility is equipped with a harness system that gently lifts subjects, simulating the Moon’s one-sixth gravity or Mars’ 38% gravity. The team enrolled six participants—four men and two women, with a median age just under 31—and put them through various exercises using the L.O.O.P. and the robotic pants. Sensors were placed over seven leg muscles, and a mask collected exhaled breath to measure respiratory gases, pulmonary ventilation, oxygen consumption, and carbon dioxide production.

Subjects then used a treadmill, walking for four minutes under each of six conditions: without the robot pants, with the robot pants but uninflated BAMs, and with inflated BAMs. They first completed all three exercises without the harness, experiencing Earth’s full gravity, and then repeated them with the harness to simulate lunar gravity. The investigators aimed to detect increased activity in the seven leg muscles and a boost in metabolic activity, both indicative of physical exertion. The findings were compelling.

Under Earth’s gravity, subjects walking with uninflated BAMs demonstrated an 18.2% increase in metabolic activity. This indicated that the mere presence of the BAMs influenced gait and exertion, making wearers work harder. When the BAMs were inflated, the metabolic rate surged by 20.1%. In the simulated lunar gravity, metabolism rose by 20.1% with uninflated BAMs and by 29.3% with them inflated. Simultaneously, leg muscle activation saw increases ranging from 13.9% to 87%, depending on the specific muscle measured.

Pulvirenti expressed his ambition to advance this technology further, with the ultimate goal of testing it on the International Space Station, as noted in a statement accompanying the study’s release.

The potential applications of this technology extend beyond space, offering benefits on Earth for injured or disabled individuals seeking to regain strength and mobility. “This exosuit is assistive, meaning it artificially boosts the lower-limb muscles, but we have also separately developed a resistive exosuit, which applies load to the body to help maintain muscle mass,” Pulvirenti explained. He added, “Our next goal is to create a hybrid suit that can switch between assistance and resistance … which could be of great benefit for people in need of support with mobility going through physical rehabilitation.” While missions to the Moon and Mars may be years or decades away, this exosuit is already poised to fulfill its purpose here on Earth.