It's the same reason that a radiator has long coils, to increase surface area compared to volume to let heat out, and because the leg is like a pendulum, the longer and thinner it is at the extremity, the more energy-efficient it is to swing.
Isti razlog je zašto radijator  ima duge zavojnice, da bi povećao površinu  u usporedbi s volumenom kako bi pustio toplinu van, i jer je noga kao visak, što je dulja i tanja na ekstremitetu, to je energetski učinkovitije  zamahivati njom.