Running with stiff legs require less energy. So why do animals have the seeming disadvantage of having squishy legs? The answer is as follows. These compliant legs provide are more effective in dealing with the force of and remaining stable in rough terrains.
Animals move in a variety of ways. A combination of mathematics and computer simulations can be used to model locomotion. However, simulated models predicted that stiff legs would be the most efficient while this is unvalidated in real life.
Smaller animals must expend more energy and take more steps to cover a given distance but still have compliant legs to stablize their motion.
Compliant legs allow an animal to move and spring through the world with less energy.
