Many human tasks such as walking, running, and hopping are repeating or cyclic tasks where assistance is needed at a repeating rate at the correct time. By utilizing resonant energy pumping, a tiny amount of energy is added at an appropriate time that results in an amplified response.
The human body is a mass spring system that oscillates up and down while running. We add energy to the running gait by oscillating a secondary mass in phase with the motion. A phase oscillator adds a bounded amount of energy to the limit cycle to make it easier to run. In an anti-phase oscillator, energy in the gait cycle is reduced and it is harder to run.
A phase oscillator based suit.