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How Does an Anti-Gravity Treadmill Work?

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The "anti-gravity treadmill" was originally invented by Robert Whalen, a biomechanics researcher at NASA Ames Research Center, in the 1990s.

Whalen knew that astronauts on the International Space Station have to exercise for hours each day to combat the loss of bone mass and muscle in microgravity. But the treadmill on the ISS has always left a lot to be desired. In lieu of gravity, it uses straps around the shoulders and hips to anchor the astronaut to the treadmill. The bungee system doesn't do a good job of replicating the magnitude or types of force that runners experience here on Earth. And to make matters worse, it's pretty uncomfortable to run in. Astronaut Sunita Williams, who was the first person to run the Boston Marathon in space, described her experience in a NASA press release: "During the marathon my foot sometimes went numb and tingly from the straps' pressure on my hip. Also, I had to use moleskin where the harness rubbed my neck raw."

NASA

Whalen designed a treadmill that would let astronauts run in a more natural way. The design, patented in 1992, encloses a treadmill and the astronaut's lower body in an airtight chamber. Lowering the air pressure inside the chamber pushes the astronaut down, simulating gravity. Whereas the ISS's old treadmill allowed Williams to run on about 60 percent of her Earth weight, Whalen's treadmill would have allowed her to exercise at her normal Earth weight. That's important for keeping the muscles and bones healthy for when astronauts get home.

But Whalen's idea never made it off the ground. In 2005, the technology was licensed to a company called AlterG, which appears to have coined the term "anti-gravity treadmill." Instead of adding weight to astronauts in space, AlterG uses the technology to take the weight off of rehab patients recovering from leg and foot injuries.

NASA

AlterG's product looks like a bounce house for your lower body. To use it, you put on a pair of tight neoprene shorts. The shorts have a sort of skirt attached, and the skirt is lined with zipper teeth. You step onto the treadmill, inside a hole in its plastic casing, and zipper yourself in so that, from the waist down, you're encased in an airtight plastic bag. As you stand there, the treadmill measures your weight, and you tell it how intense you want your workout to be. The the machine uses "unweighting technology" to make you feel up to 80 percent lighter—so if you weigh 100 pounds, you could feel as light as 20 pounds on the treadmill. The terms "anti-gravity" and "unweighting technology" are enthusiastic descriptions for what the machine actually does, which is inflate the plastic bag around your lower body to lift you off the surface of the treadmill.

Despite its perhaps overhyped name, the anti-gravity treadmill seems to be doing good things in physical rehab clinics, because it allows patients to exercise without exacerbating an injury. Here's NASA's glowing review of the anti-gravity treadmill:

Professional and college sports teams across the United States feature the AlterG treadmill in their training facilities. Injured soldiers walk and run with the technology’s assistance at military hospitals and rehabilitation centers. Seniors get essential exercise using the support the machine provides, as do people with bariatric weight issues who cannot normally support their own weight. The treadmill has been a proven option for neurological uses as well, including helping patients re-learn proper balance and gait and transition to independent movement after traumatic brain injury.

A variety of peer-reviewed studies also suggest it helps people get back on their feet again.

A true anti-gravity machine—one that is not acted on by gravity—would of course have even more exciting applications, particularly in spaceflight. Unfortunately, for now at least, those machines only work in science fiction.

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Big Questions
Why Does the Queen Have Two Birthdays?
CHRIS JACKSON, AFP/Getty Images
CHRIS JACKSON, AFP/Getty Images

On April 21, Her Majesty Queen Elizabeth II will turn 92 years old. To mark the occasion, there are usually a series of gun salutes around London: a 41 gun salute in Hyde Park, a 21 gun salute in Windsor Great Park, and a 62 gun salute at the Tower of London. For the most part, the monarch celebrates her big day privately. But on June 9, 2018, Her Majesty will parade through London as part of an opulent birthday celebration known as Trooping the Colour.

Queen Elizabeth, like many British monarchs before her, has two birthdays: the actual anniversary of the day she was born, and a separate day that is labeled her "official" birthday (usually the second Saturday in June). Why? Because April 21 is usually too cold for a proper parade.

The tradition started in 1748, with King George II, who had the misfortune of being born in chilly November. Rather than have his subjects risk catching colds, he combined his birthday celebration with the Trooping the Colour.

The parade itself had been part of British culture for almost a century by that time. At first it was strictly a military event, at which regiments displayed their flags—or "colours"—so that soldiers could familiarize themselves. But George was known as a formidable general after having led troops at the Battle of Dettingen in 1743, so the military celebration seemed a fitting occasion onto which to graft his warm-weather birthday. Edward VII, who also had a November birthday, was the first to standardize the June Trooping the Colour and launched a tradition of a monarchical review of the troops that drew crowds of onlookers.

Even now, the date of the "official" birthday varies year to year. For the first seven years of her reign, Elizabeth II held her official birthday on a Thursday but has since switched over to Saturdays. And while the date is tied to the Trooping the Colour in the UK, Commonwealth nations around the world have their own criteria, which generally involve recognizing it as a public holiday.

Australia started recognizing an official birthday back in 1788, and all the provinces (save one) observe the Queen's Birthday on the second Monday in June, with Western Australia holding its celebrations on the last Monday of September or the first Monday of October.

In Canada, the official birthday has been set to align with the actual birth date of Queen Victoria—May 24, 1819—since 1845, and as such they celebrate so-called Victoria Day on May 24 or the Monday before.

In New Zealand, it's the first Monday in June, and in the Falkland Islands the actual day of the Queen's birth is celebrated publicly.

All in all, just another reason it's great to be Queen.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
What Is the Meaning Behind "420"?
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Whether or not you’re a marijuana enthusiast, you’re probably aware that today is an unofficial holiday for those who are. April 20—4/20—is a day when pot smokers around the world come together to, well, smoke pot. Others use the day to push for legalization, holding marches and rallies.

But why the code 420? There are a lot of theories as to why that particular number was chosen, but most of them are wrong. You may have heard that 420 is police code for possession, or maybe it’s the penal code for marijuana use. Both are false. There is a California Senate Bill 420 that refers to the use of medical marijuana, but the bill was named for the code, not the other way around.

As far as anyone can tell, the phrase started with a bunch of high school students. Back in 1971, a group of kids at San Rafael High School in San Rafael, California, got in the habit of meeting at 4:20 to smoke after school. When they’d see each other in the hallways during the day, their shorthand was “420 Louis,” meaning, “Let’s meet at the Louis Pasteur statue at 4:20 to smoke.”

Somehow, the phrase caught on—and when the Grateful Dead eventually picked it up, "420" spread through the greater community like wildfire. What began as a silly code passed between classes is now a worldwide event for smokers and legalization activists everywhere—not a bad accomplishment for a bunch of high school stoners.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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