INTRODUCTION

Elastomeric proteins play many important roles in the lives of animals. They enable animals ranging from fleas to large mammals to jump further than would otherwise be possible. They save energy in locomotion for galloping horses, hopping kangaroos, flying flies, and swimming jellyfish. They make clam shells spring open when the muscles inside relax, they help to support the heavy heads of cattle, they smooth the flow of blood round our bodies, and they cushion the impact of our heels on the ground. This chapter attempts to explain briefly how they do all these things.

POWER AMPLIFIERS

Catapults are power amplifiers. The rubber is stretched in preparation for shooting, storing up strain energy. This can be done slowly; but when the catapult is released, the rubber recoils very rapidly, returning the stored energy as kinetic energy of the missile. The work done by the recoiling rubber is (almost) equal to the work previously done stretching the rubber; but, it is done in a much shorter time so the power (rate of doing work) has been amplified. Using a catapult, I can project a missile much faster than I can move my hand.

Catapults are useful because the power output that can be obtained from a muscle is limited. For example, Peplowski and Marsh (1997) made physiological measurements on a leg muscle of a tree frog and found that the highest power output obtainable from it was 240 W/kg. However, they calculated that the power required for the longest jumps, which it could make at the same temperature, was about 800 W/kg muscle. They concluded that a catapult mechanism must be involved.