The manipulation of frequency (rate of vibration) and amplitude (size of movement) creates what is known as acceleration, which can be compared to g-forces on earth. Our bodies are accustomed to and respond to the gravity on earth, which is defined as one g-force. The force of gravity the body experiences is dependent on mass (weight), so by increasing mass (such as lifting a barbell or dumb-bell) your body builds strength to cope with the increase in force.
Training on a Power Plate® machine however manipulates acceleration, therefore creating an environment where the body is stimulated to increase force due to higher g-forces, without the need for additional loads being placed on the muscular-skeletal system.
The rapidly moving surface stimulates the body's reflexes to induce the responses needed to keep the individual upright and allows the muscles to produce more force on an unconscious level. The physiological evidence of this improved muscle strength can be seen through neurological and myogenic adaptation.