Today's technology is so sophisticated because they have came up with more materials that are stronger, more flexible, lighter weight, and more durable. The various ways they work are:
1.- The carbon graphite stores kinetic energy in each step allowing amputees to walk, run, and jump faster.
2.- Robotics or bionics can produce energies greater than what a spring can produce.
3.- The SACH foot stores little to no energy nor returns little to no energy.