Fat king penguins are unsteady on their feet while waddling compared to their slimmer counterparts, making them an easier catch for predators (or pesky scientists).

A UK research team discovered this by simply travelling to the subantarctic region of Antarctica, catching 10 male king penguins and putting them on a treadmill. Okay, it wasn't quite as simple as that but it does mean we can watch penguins on a treadmill.

The team, led by Astrid Willener from the University of Roehampton, was studying the biomechanics of the waddle of the king penguin, which can grow up to 1m tall and up to 16kg, making it the second largest species of penguin behind the emperor.

They captured 10 males who were in courtship and weighed more than 12kg near the shoreline at the edge of a colony. The penguins, serial monogamists, have the longest breeding cycle of all the penguin species – 14 to 16 months – and produce just one chick per cycle. Anyone who has seen March of the Penguins knows that caring for a penguin egg requires enduring an intensely long fast, so it's crucial that parents have enough fat to keep them going.

The captured penguins, who were kept beside the colony for two weeks, received two training sessions of 10 minutes to get used to walking on the treadmill. Then they were filmed at a speed of 1.4km/hr before and after a 14-day fast (fasting for periods of up to one month is normal for king penguins and researchers checked the critical body mass of the birds to be sure that they were not losing body mass too fast during the study).

The posture – leaning and waddling – of the penguins while walking was then determined by the researchers. To quantify the waddling, the amplitude of peak left and right leaning was calculated.

It wasn’t all simple though. Some of the penguins – the larger individuals – found ways to cheat the system.

“ Sometimes the penguins were lazy and ‘water-skied’ on the treadmill by leaning their back on the back wall of the treadmill. That is obviously not good for the data collection,” Willener told the Guardian.

In the end the researchers found that although the penguins waddled with more agility at a lower weight, they had nonetheless adapted well to be able to handle waddling while heavier, even if they were not as efficient and less stable.

And packing on the pounds did give the big guys an important advantage when it comes to reproduction, the study, which was in the online journal PLoS One, found.

“The weight gain is an adaptive mechanism for them to survive their fast while reproducing and taking care of the egg,” said Willener. “But it is a trade-off between putting on weight to fast longer, in case there is a delay in finding a penguin partner to mate with, and still being able to walk, because if they can’t walk steady, they fall and will be spotted and eaten alive by predators.” Luckily walking isn’t their primary travel mode.

Willener hopes the findings will help in efforts to better understand, and protect the species.

The scientists were careful to point out that the video of its chubby penguin has been sped up, so it appears to be running faster than it did in reality. And, they clarify, no penguins were pushed over during the process.

So, you get to watch penguins on a treadmill and relax in the knowledge that it’s not only humans who put on weight when they’ve got a new girlfriend.