For millennia, humans have been drawn to explore the cosmos. Since Apollo 11 astronauts first set foot on lunar soil in 1969, more than 72 countries have established their own space programs. And with NASA’s plans to establish a sustained presence on the moon by 2028, including a possible staging point for future missions to Mars, human space exploration is expected to rocket forward in the years to come.

But any space-bound travelers may have to contend with a surprisingly mundane (and highly common) terrestrial problem: back pain.

More than half of space travelers experience some form of back pain during their voyage, according to a report by a team of researchers and physicians published in the journal Anesthesiology in 2021. While most back pain in space tends to fade on its own, the scientists predict that the number of people suffering from such discomfort will increase alongside the projected surge in the number of humans voyaging beyond our atmosphere.

What’s more, further study of methods to prevent, diagnose and treat back pain among astronauts — like specialized spacesuits and certain kinds of exercises — may benefit Earthbound humans battling aching backs, as well.

Back Pain and Outer Space

You don’t need to float in microgravity or clamber aboard the International Space Station to feel the strain of a throbbing back.

Nearly 65 million Americans experience back pain at any given time, with around 16 million adults suffering from chronic pain that limits their daily activities. In the U.S., it’s the sixth most costly medical condition, racking up $12 billion per year in health care and related costs.

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“In some populations, it’s the leading cause of disability in the world,” says Steven P. Cohen, one of the report’s co-authors and a professor of anesthesiology and critical care medicine at Johns Hopkins Medicine. “And pretty much everyone gets back pain — if you are physically active, you will get back pain, even if it’s not reported.”

In their report, the scientists performed a comprehensive review of prior studies analyzing space travel’s impacts on the spine. Their review showed that 52 percent of space travelers experienced back pain in the first two to five days of spaceflight as they adjusted to microgravity, based on a study of 722 space flights published in Aerospace Medicine and Human Performance in 2012.

While most cases were transient and mild, and 90 percent of astronauts found relief by performing movements like flexing the spine or curling their knees to their chest, the discomfort still inhibited their ability to perform tasks.

Although most cases of the condition, dubbed “space adaptation back pain,” are limited to those first few days in microgravity, the stress of shifting gravitational forces can still cause issues like disc herniation — an injury to the rubbery sliver of tissue between the spinal bones. Astronauts are at least four times more likely to herniate a disc than the general population, according to a 2010 NASA study, particularly in the immediate aftermath of their arrival back on Earth.

What Causes Back Pain in Space?

Scientists still haven’t figured out exactly why back pain is so prevalent among astronauts.

“The reasons for that are not clear,” says Cohen. “But it probably has to do with the stretching of the ligaments that can happen [in microgravity].”

That’s because our spines are designed to support our bodies under gravitational pressures on Earth — particularly the spinal curvature, an S-shaped bend that allows our bodies to resist gravity, stay flexible and absorb weight and impact. In microgravity, that curve is flattened.

Data from the earliest explorations into space, the researchers found, indicate that astronauts gained an extra 3 inches in height from the loss of their spinal curve. Upon returning to Earth, that curve typically returns.

More recently, MRI scans found that modern astronauts developed a flattened spine in microgravity, as well, according to a study published in The Spine Journal in 2018. The scientists suggest that doesn’t just potentially contribute to their acute pain, but also raises their risk of injury when they land on Earth and feel the full weight of gravity again.

Still, there are other possible contributors beyond the contortions of microgravity — such as the intense physical pressure involved with blasting into space on a shuttle capable of hitting 17,500 mph. Changes in astronauts’ dietary habits can also alter nutritional levels, potentially impacting tissue health and healing.

Treating Back Pain in Space — and Beyond

Fortunately, astronauts have been standing tall against these stressors for decades.

Throughout the Space Age, the researchers say in their report, resistance exercises — from isometrics and squats to lunges and bench presses — have been a staple of back pain prevention. But while exercise machines and other resistance training equipment on some space stations can help prevent and soothe symptoms it’s still a massive time sink, requiring astronauts to spend two to three hours per day working out while floating in microgravity.

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There are other countermeasures, too. Specialized suits can provide spinal resistance that mimics the pressures felt under Earth’s gravity. For example, the recently redesigned Gravity Loading Countermeasure Skinsuit progressively increases the tension an astronaut feels on their limbs and spine.

Other methods mentioned in the report include preventative massages and nutritional supplements before and during space travel. There’s also emerging tech like neuromuscular electrical stimulation, which would use specialized devices to send electrical impulses that cause certain muscles to contract after an expedition.

Other advances might even benefit us on Earth, as well. Cohen points to long-distance truck drivers, who are at risk of developing back problems, partially due to the vibrations they feel as their vehicles rumble along.

“If we can develop better means to insulate pilots and astronauts, then we might be able to do the same thing for truck drivers,” says Cohen. “And if we can devise more sensitive means to detect pathology within discs, joints and ligaments, then this could benefit everyone — the population as a whole”

Still, Cohen notes that more sensitive diagnostics have the potential to cut both ways, meaning that they could help identify which patients need additional support, but could also be extensively applied to back issues that may not require treatment. “You’d just have to be cautious in using it,” he says.