May 27, 2014 05:02 AM EDT By Staff Reporter, UniversityHerald Reporter

Brown University researchers have solved the mystery behind how bats fine-tune their flight.

The researchers said that the answer lies in the hair-thin muscles - plagiopatagiales - embedded in the membrane of their floppy wing skin. The network of tiny muscles regulates wing stiffness, curvature and shape, thus enhancing aerodynamic performance.

"Aerodynamic performance depends upon wing shape," said Jorn Cheney, biology graduate student and lead author, in a press release. "The shape of a membrane wing might initially begin flat but as soon as it starts lifting it's not going to remain flat because it has to deform in response to that aerodynamic load."

"The shape it adopts could be a terrible one - it could make the animal crash - or it could be beneficial," Cheney said. "But they are not locked into that shape. Because bats have these muscles in their wings, and also bones that can control the general shape as well, they can adopt any number of profiles."

For the study, the researchers attached electrode sensors to a few muscles on the wings of some Jamaican fruit bats and recorded them as they flew in the lab's wind tunnel. Researchers hypothesized that either the oddly shaped, weak muscles activated together in the flight or acted solely as stretch sensors.

The researchers found that muscle activation and relaxation follows a specific pattern during flight. They tense on the down-stroke and relax on the up-stroke. Plagiopatagiales acted together to provide enough strength to stiffen the wing. The muscles were associated with active behaviour to keep with the conditions of flight.

Co-author Sharon Swartz, professor of biology, said that this is the first study that demonstrated switching on and off of muscles in bats during a usual wingbeat cycle.

The findings could allow researchers to use bats' muscle mechanism to create flying robots. Currently, researchers are improving a robotic wing by incorporating the findings from this study.

"When one tries to build an engineered flying vehicle, you want to have control over its aerodynamic properties," said co-author Kenneth Breuer, professor of engineering. "This is one more knob that we have to turn now. To be able to use these membrane wings and be able to control the properties in the way that we suspect bats do, using these muscles, is a great opportunity for biomimetic systems."

The finding is published in Bioinspiration and Biomimetics.

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