NASA recently ran tests to see how fast astronauts can run on the moon, and discovered they're speedier than previously believed. 

The study, which was released on Wednesday, was held on the space agency's DC-9 aircraft, which can reduce its internal gravity to that of the moon while flying, according to The Verge. Eight participants, three of whom were actual astronauts, ran on a treadmill for 20 seconds at lunar gravity.

John De Witt, study co-author and senior biomechanist at the NASA Johnson Space Center, said the participants didn't always have fun during the testing.

"If you get sick you're done...We wanted to be sure we had people that were used to flying," De Witt said.

Despite the issues, the test subjects were able to exceed the scientists' expectations, The Verge reported. The NASA scientists expected in their theoretical calculations that the participants would have an average walk-to-run transition speed of about 1.8 miles per hour, but their average transition speed turned out to be 3.13 miles per hour. The results were much closer to the average transition speed that humans have on Earth.

De Witt believes the participants were able to achieve this speed because of the counter-swinging movement of their arms and legs. He said because Earth's gravity is stronger than the Moon's, the force exists at a smaller level on Earth.

The study was published in the Journal of Experimental Biology.