The Amplitude is the intensity of the stimulus increases, so does the strength of the contraction. The force of the contraction has been found to be linearly related to the amount of current introduced into the tissues. The higher the intensity the deeper it peaks into the muscle tissues thus, recruiting more nerve fibers. However it is said to be the pain of the stimulation that prevents maximal contractions from being achieved. Cold treatments are often used to help reach a stronger contraction, because it is said to dull the discomfort of the stimulation. .
Frequency is the other part of these contractions, controlling when and for how long they occur. For instance when stimulation is applied for less than 15 pulses per second, there are distinguishable muscle contractions for each pulse. At this rate the muscle fibers return to original length before the next pulse begins. But as the pulses become greater the contractions become less and less distinguishable due to summation, which means that the muscle fibers do not return to their original length before the start of the next pulse. "Summation continues until the muscle reaches the stage of tetany-. At this point, the muscle enters a tonic contraction. Increasing the frequency of the stimulation will do little to further smooth, the muscle tone. It will, however, promote muscle fatigue. If used for a sufficient length of time. The amount of frequency pulses required is different for different muscle groups. "A strong tetanic contraction is required to delay atrophy or enhance strength."".
"Each muscle has one or more skin surface areas that are hypersensitive to electrical current flow (motor points)-. These discrete areas are areas that blood vessels enter the muscle mass. "Because of their low electrical resistance, stimulation of these points will elicit a stronger contraction at a lower intensity tan the surrounding tissue-. These areas may vary person to person and over time may tend to vary on a single person that has been going through stimulation on a certain spot over a period of time.