Waddling Helps Penguins Save Energy

Dec. 20, 2000 -- Sure, penguins walk funny, but there’s a good reason for their side-to-side gait. New research shows waddling is a smart way for the tuxedoed birds to get around — and could help humans, too.

Even though penguins’ efforts to move forward may seem futile and exhausting, a new study by University of California at Berkeley researchers published in the latest issue of the journal Nature shows how waddling actually helps the birds conserve energy.

The waddling research has implications not only for penguins, but for pregnant women and other humans who have difficulty moving around due to disabilities, neurological problems or obesity, say the researchers.

The Culprits: Short Legs

Scientists have long known how inefficient walking is for penguins. The flightless birds, found on cold-climate seacoasts in the Southern Hemisphere, use many more calories than other animal species of the same weight to walk or run.

But that’s not because they do extra work with their muscles, therefore tiring themselves out. Walking is “expensive” for penguins because they have short legs and must rapidly generate force with their muscles to keep their legs rigid during each step, the researchers say.

The bottom line: Faced with a stout body, tiny legs and big feet, penguins have devised an evolutionary tradeoff and waddle to save strength.

The scientists were surprised at what they learned about how penguins move. “Going into the study, we expected to find that penguin walking was expensive because their side-to-side waddling disrupted the smooth exchange of energy from step to step,” said Rodger Kram, a co-author of the study and former University of California researcher now at the University of Colorado-Boulder. “But instead we found the opposite; they have smooth energy exchange.”

Penguins Act Like Pendulums

Five emperor penguins at San Diego Sea World’s “Penguin Encounter” exhibit, a large refrigerated “penguin city,” served as the test subjects of the study. The Sea World staff, along with the Berkeley scientists and their students, prodded the penguins across a platform to measure the side-to-side and forward and backward forces they exert while walking, plus the vertical forces supporting their weight.

Emperors are the largest penguins, weighing around 40 pounds and standing more than 3 1/2 feet tall. The penguins’ normal walking speed was about 1.5 feet per second.

Based on their measurements, the researchers discovered that waddling helps the penguin walk more efficiently.

“The penguin’s rocking motion helps raise their center of mass,” said Timothy Griffin, a co-author and integrative biology graduate student in UC Berkeley’s College of Letters & Science. “Without it, their muscles would have to make up that work.”

How penguins save energy through waddling is analogous to an inverted pendulum swinging back and forth, the researchers say. At the end of each swing, when the penguin is still and poised for the next swing, the energy of side-to-side motion is stored. On the return swing, this energy is converted into motion as the penguin rocks back through the upright position.

The energy again is stored as the penguin comes to a stop at the opposite extreme. The penguins also rock forward and backward as they move, employing the same inverted pendulum motion used by all animals, even those with four legs, the researchers said.

Research Could Help Humans

The percentage of energy retained during two steps is called the recovery rate. Humans have a recovery rate of about 65 percent. The penguins studied by Griffin and Kram had a recovery rate of up to 80 percent.

In the past, Kram said, his research focused on animals who moved gracefully and efficiently, like dogs, kangaroos and antelopes. But it seems that the least efficient animals have a lot to teach us, he said.

Through their research on penguins, humans who have problems walking could benefit someday, the scientists said.

“This study of penguins is thus giving us a broader message that when we try to evaluate humans who have difficulties walking, we should not be so concerned about the work their muscles do, but rather how their muscles must generate force to support their body weight,” Kram said.

The penguin research could help scientists as they try to design walking devices and devise surgical strategies for humans, he said.