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Running might be one of the most dreaded forms of exercise for humans, but for mice, running appears to be highly enjoyable. According to a new study conducted in the Netherlands, mice like to run on the wheel even when they are not caged.

"When running wheels are placed in nature, they are frequently used by wild mice, also when no extrinsic reward is provided. Bout lengths of running wheel behavior in the wild match those for captive mice," the researchers wrote. "This finding falsifies one criterion for stereotypic behavior, and suggests that running wheel activity is an elective behavior."

For this study, the researchers from Leiden University Medical Center wanted to know if running on a wheel was linked to neurotic behavior developed from living in a cage. The research team was also curious to find out if running was a behavior caused by stress for wild mice. The team conducted an experiment where they placed exercise wheels outdoors in the wild. The wheels were monitored with motion detectors and cameras, which recorded 12,000 clips. The researchers discovered that wild mice voluntarily ran on the wheels.

"When I saw the first mice, I was extremely happy," said Johanna Meijer, a brain electrophysiologist who studies biological rhythms in mice, reported in TIME. "I had to laugh about the results, but at the same time, I take it very seriously. It's funny, and it's important at the same time."

She added, according to ABC Science, "Locomotion can be inherently rewarding for animals. Our results indicate that running wheel activity is not necessarily an aberrant behavior initiated as a consequence of captivity and perhaps stress, but rather an elective behavior that can be observed in a natural environment."

The researchers added that the second most common user of these wheels was the slug. Slugs showed up on camera sliding along the wheels for hours. After the slugs, the researchers noted that frogs frequented the wheels quite often as well. Unlike the mice, the frogs did not run or walk on the wheels. Instead, they chose to sit and jump.

The study, "Wheel running in the wild," was published in the Proceedings of the Royal Society B.