Collagenous Tendons Store Work

Biological Strategy

Red kangaroo

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Store Energy

Once a living system captures energy or transforms one energy form into another, it must frequently save that energy for future use. But energy is difficult to store in some forms. So living systems need strategies to either use energy quickly, or to convert it from forms that are difficult to store (such as electrical or kinetic) to more storable forms. For example, grasshoppers store energy as potential energy in an elastic material in their tendons. When they need to jump, that energy converts into kinetic energy, providing the force needed to escape predators.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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Collagenous tendons in the legs of jumping kangaroos allow them to recover work done on the legs in landing by transferring much of the force of the muscles to bones.

“What about the biological role of collagenous tendons? They usually run between the ends of a muscle and its attachments to bones, so the force (and shortening) of the muscle is transmitted to the bones. Work is stored–in a running person or hopping kangaroo about 40-50 percent of the work done on a leg in landing is recovered as it pushes off again (Alexander 1983). The leg tendons do most of that storage despite their low mass relative to bones, muscles, or the animal as a whole.” (Vogel 2003: 345)

Vogel S. Comparative Biomechanics: Life’s Physical World. Princeton: Princeton University Press; 2003. 580 p.

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