These machines use a technology called isoinertial. It consists of a set of mechanisms that reinforce the eccentric part of the movement. Remember that many movements are made up of three phases: concentric (against gravity), isometric (where muscle contraction is maintained but without movement) and eccentric (slowing down the action of gravity). Well, it has been scientifically proven that emphasising the latter phase will help prevent injuries. The structural basis of these machines lies in flywheels or flywheels. When we apply force in the concentric phase, the machine stores the kinetic energy generated in various ways. This is returned in the eccentric phase and the subject will have to brake this inertia.