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Escaping the Earth’s orbit and floating through space for a six-month mission results in an average bone loss equating to nearly two decades of bone loss on earth. That means a 40-year old astronaut returns to Earth with a 60-year old skeleton.

Findings from the TBone study, published in the , reveal that bone loss progresses with the length of a space mission despite daily exercise programs designed to prevent bone loss.

• Photo above: The mission patch for the TBone project. Photo was taken by Canadian Space Agency astronaut David Saint-Jacques during his mission aboard the International Space Station. Photo courtesy Canadian Space Agency

“With astronauts on missions of varying space flight durations, we were able to analyze the trajectory of bone loss and confirm that bone loss progresses with the length of the mission and does not stabilize for up to seven months in-flight,” says lead author Dr. Leigh Gabel, PhD, a postdoctoral fellow at the Cumming School of Medicine (CSM).

Even though many of us may never step foot on the moon, the study findings are relevant to understanding bone loss on Earth and the impact of decreasing use of weight-bearing bones due to injury or immobilization. Space travel research on bone loss shows changes in bone that would typically take decades to study.

Using 3D imaging from a high-resolution peripheral quantitative CT, which can measure bone on a scale finer than human hair, bone structure of an arm (radius) and leg (tibia) bone were recorded pre-flight and after returning from space. Blood and urine samples were also taken in-flight to measure biomarkers of bone turnover and astronauts’ exercise was recorded pre-flight and in-flight. During space flight, astronauts participated in extensive in-flight training that included cardio and resistance training at the International Space Station (ISS).

Findings reveal the astronauts who trained heavily before space flight reduced their training volume in-flight and witnessed greater bone loss in the weight-bearing tibia with little change to the radius. Similar findings were seen for resistance training, although astronauts who increased resistance training during space flight protected some of their bone strength.

“Increasing exercise training before space flight is counterintuitive since it’s hard to maintain the level in space. Bone changes due to microgravity plus the reduction in exercise levels can result in further bone loss,” says Dr. Steven Boyd, PhD, principal investigator and director of the McCaig Institute for Bone and Joint Health at the CSM.

The impacts pre-flight and in-flight training levels on bone loss suggest that astronauts who frequently trained before space flight may require different in-flight training. “The findings of the study relay the importance of noting pre-flight exercise when designing in-flight exercise programs so astronauts can try to maintain the level of training on-orbit to preserve their bone strength,” says Gabel.

Long-term impacts of bone loss from space are still unknown and there is little research on whether bone loss is reversible. “Future research needs to look at whether bone can recover and if the changes in bone microarchitecture are permanent,” says Boyd, professor at the Schulich School of Engineering, the Faculty of Kinesiology and the CSM. “Upcoming TBone studies will look at what happens after a year of space flight and whether bone loss stabilizes in orbit.”