Fat penguins: they're a thing. They're not just chubby because they're stress-eating squid, however; male King Penguins gain weight so that they can live off their fat reserves while protecting their eggs. But this can make the penguins less agile,so researchers at the University of London, led by Astrid Willener, took on the very important task of putting penguins on treadmills to see how their agility changed with weight loss.
The Guardian provided this hilarious, if not quite journalistically sound, video from the experiment where the original video has been sped up and paired with jaunty music, giving the experiment a Benny Hill vibe:
The researchers discovered that the penguins did waddle better when they were trimmer, but that they "had nonetheless adapted well to be able to handle waddling while heavier." They do, however, tend to be stabler when they weigh more.
Perhaps even more important was the discovery that, like humans, penguins try to cheat their exercise routine. Willener noted that, "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." No, but it's great for humans being able to justify their laziness by pointing out that penguins avoid exercise too.