Division Of Movements

Ling and his pupils divided the movements into :
1. Single.
2. Double.
The single movements they again subdivided into passive and active, and the double movements into concentric and excentric.
Passive movements are such as are applied to the patient without his assistance. (They may be performed by an operator, by a machine, or through the power of gravity.)
Active movements are performed by the patient
Concentric (active-passive) movements are performed by the patient, while the operator or some other power resists.
Excentric (passive-active) movements are performed by some power outside of the patient, while he resists.

The principal difference between the concentric and excentric movements is that in the former the muscle is shortened, in the latter it is stretched. As to their nature and physiologic action, it is easy to understand that they are but little different from the single active movements. Practically they are of great use, as by them we are able to exactly fix the amount of mechanical work done by the patient in each movement. To make the terminology somewhat simpler for the reader, we have in the description of the movements used the expression duplicated active movements, by that covering both concentric and excentric movements in the Ling system.