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Resistive, Targeted Exercise Reversed Astronauts’ Bone Loss, Study Finds

NASA astronaut Kevin Ford, Expedition 34 commander, uses the short bar of the advanced resistive exercise device to perform upper-body strengthening pull-ups in the Tranquility node of the international space station. Credit: NASA photo

BOSTON International space station crew members who used a resistive exercise device that targets key parts of the body returned to Earth with dense bones and leaner bodies, a complete reversal from previous long-duration spaceflights, NASA scientists reported at the American Association for the Advancement of Sciences meeting here on Feb. 18.

NASA launched the Advanced Resistive Exercise Device (ARED) to the space station in 2008 in an attempt to home in on specific areas of the body most prone to bone loss in zero gravity, including the hip, pelvis, top of the thigh and lumbar spine.

“We used to see 1 percent to 2 percent per month loss of bone mineral density in all those regions. The maximum I ever saw was 22 percent bone loss in the lumbar spine after six months,” said NASA astronaut and physician Michael Barratt, who spent 6.5 months aboard the space station.

“As long as you’re unloaded up there, you’re going to be losing bone, you’re going to be losing calcium and you’re going to be losing muscle,” Barratt said.

Typically, astronauts would return to Earth with a total of 4 percent to 5 percent of their body mass gone.

“Now, it’s a rule to have it more or less unchanged,” Barratt said. “We’re seeing insignificant changes in bone density. We’re actually seeing an increase in lean body mass and decrease in body fat. Until just recently, I would have given you absolutely opposite information.”

Doctors credit better nutrition and the ARED, which Barratt describes as a “monstrosity” that allows up to 270 kilograms of continuous force on specific areas of the body most vulnerable to bone loss in zero gravity. In addition to 90 minutes a day of resistive exercise, astronauts typically spend about 30 minutes a day on a treadmill or exercise bike.

“This is the first evidence that improving nutrition and resistance exercise during spaceflight can attenuate the expected (bone mineral density) deficits previously observed after prolonged missions,” NASA researcher Scott Smith and colleagues write in the peer-reviewed Journal of Bone and Mineral Research, which published the study.

“We still have a couple of places that we have to work on, but those are in the very tiny, single-digit percent of loss and most likely this is a fine-tuning of our loads and exercise angles,” Barratt added.

The research has implications for treating osteoporosis and osteopenia, conditions that are particularly threatening to post-menopausal women.

“We’ve always treated post-menopausal women by telling them, ‘Don’t do anything too resistive, you might break your hip. Just walk a little.’ We’ve actually directed women to do the wrong kind of exercise and then put them on meds,” Julie Robinson, NASA’s chief space station scientist, told SpaceNews. “What about someone who has a risk of osteoporosis, whose bone mass density hasn’t gone down that much so their fracture risk isn’t high yet? Maybe they should be doing high-resistance exercise. No one has done that study on the ground.

“This finding in one population makes you rethink standard approach in another. In the end, keeping astronauts’ bones safe is good for space missions, but the whole point is that it should be good for more than that.”

The study compared diets, bone mineral density and biochemical markers of 13 space station crew members who flew between 2006 and 2009. Eight used the less-sophisticated Interim Resistive Exercise Device (IRED) and five had access to the ARED. The IRED allowed loads of up to 135 kilograms of force, but did not target specific areas of bone loss.

The resistive exercise, however, may have a downside. Doctors have been puzzled over the cause of recently discovered vision deterioration in astronauts, believed to be associated with intracranial pressure and fluid shifts in weightlessness.

“Of the five people we’ve done post-flight spinal taps on, we find slightly increased intracranial pressure. That is surely part of this syndrome,” Barrett said. “High-resistive exercise, coupled with this issue of fluid shift, might contribute.”

A paper describing the ophthalmic changes and potential contributing factors is pending publication in Acta Astronautica.

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