Flying Frogs

Exceptional frog leaps fit for David Attenborough nature documentaries are not all thanks to muscle power. A recent study published last week in Biology Letters unveiled that the secret lies in the springy tendons of frogs.

Scientists have known for a while that such feats cannot be accounted for by muscular effort alone. In some frog species, the total power generated for a jump can be as many as seven times more than the maximum muscle power. So where is the majority of power generated? Complementing the muscles are tendons at the ankles which store energy before catapulting the frogs.

As a frog prepares itself to jump, its leg muscles shorten in anticipation. However this does not immediately result in joint movement. Instead, the muscle shortening causes stretching of the tendons which accumulate energy. Then, the tendons recoil like springs and release this stored energy. The ankle joints move allowing the limbs to straighten so as to propel the frog upward. And the frog flies-more or less.

The scientists used high-speed cameras and a new technology called X-ray reconstruction of moving morphology (XROMM) to track movements of muscles and bones in four frogs. By implanting radiopaque beads in leg muscle, affixed to bones of the ankle joint, the scientists were able to use this technology to visualize in 3D how the muscle and bones move during jumping.

They found that muscle shortening which occurs at the onset of a jump started 100 milliseconds before joint movement. The only possible reason why the muscle shortening does not immediately result in joint movement is that the tendons at the ankles are being stretched. During those 100 milliseconds, the tendons were stretching and storing energy which was then released as the tendons recoiled to catapult the frogs.

This study conclusively demonstrated a synergy between muscles and tendons in frogs. It also is proof that you don't necessarily need great muscles to show off on TV.

Image credit: Brian Gratwicke (from Wikimedia Commons)

Reference: Astley, H.C. and Roberts, T.J. Evidence for a vertebrate catapult: elastic energy storage in the plantaris tendon during frog jumping. Biology Letters (2011)