Five birds were encouraged to waddle across a special platform that measured the side-to-side and fore-and-aft forces they exerted as they walked. The vertical forces supporting the animals' weights were also recorded.
And conserving energy is vitally important for an animal that may have to walk more than 100 kilometres across the freezing Antarctic ice to find open water in which to swim and fish.
The gaits of penguins might seem an odd thing to study, but scientists say such work can aid our understanding and treatment of people with walking disabilities. It can even lead to better robotic design and more realistic figures in animated films.
Cutting losses
Researchers from the University of California, Berkeley, US, performed their experiments on Emperor penguins at the San Diego SeaWorld park.
Five birds were encouraged to waddle across a special platform that measured the side-to-side and fore-and-aft forces they exerted as they walked. The vertical forces supporting the animals' weights were also recorded.
From this, the scientists were able to show that although penguins are inefficient walkers, the birds would waste far more energy if they did not waddle.
"Our hunch was that if penguins were trying to move forward, but expended energy rocking side to side with this awkward, roly-poly, back-and-forth movement, then it had to be wasted energy," said researcher Professor Rodger Kram.
"But what we found was that they were inefficient because of their short legs and big feet, and waddling was a means to cut their losses."
But their apparent awkwardness on land is more than compensated by their elegance in water.
"Penguins are rare among birds in that they stand upright, and that's probably so they have better control of heat when insulating eggs, but it's also so they're built better when they swim," Professor Jeremy Rayner, an expert on animal locomotion at the University of Leeds, UK, told BBC News Online.
Professor Rayner said the US study appeared to show that penguins were making the best of their design on land. "Some of these animals do enormous long-distance walks across Antarctica and although we'd think that waddling is inefficient, biologically it can't be. And looking at this study, it seems the researchers have found out why and they've demonstrated how."
The Berkeley team said their work could have practical benefits. "Our knowledge gained from penguins provides novel insight into the gait mechanics of humans with increased lateral movements, such as in pregnant women or obese individuals. This information may lead to improved understanding, evaluation and treatment of individuals with gait disabilities."