The activator is a small handheld spring-loaded instrument which delivers a small impulse to the spine. It was found to give off no more than 0.3 J of kinetic energy in a 3-millisecond pulse. The aim is to produce enough force to move the vertebrae but not enough to cause injury
The activator method chiropractic technique (AMCT) involves having the patient lie in a prone position and comparing the functional leg lengths. Often one leg will seem to be slightly shorter than the other. The chiropractor then carries out a series of tests such as pressing on a vertebra. If the shorter leg seems to become even shorter, that is taken as a sign that the problem is located at that vertebra. The chiropractor treats problems found in this way moving progressively along the spine in the direction from the feet towards the head.
Although prone "functional leg length" is a widely used chiropractic tool, it is not a recognized anthropometric technique, since legs are often of unequal length, and measurements in the prone position are not entirely valid estimates of standing X-ray differences. Measurements in the standing position are far more reliable. Another confounding factor is that simply moving the two legs held together and leaning them imperceptibly to one side or the other produces different results. Fuhr claims that properly trained doctors show good interexaminer reliability.