yogabook / movement physiology / ROM

range of motion ROM

The entire range of motion/movement (also: traffic space, movement space) of a joint (ROM) in all directions up to its respective end. With reference to a coordinate system, for example corresponding to vectors on the usual movement directions, which (opposite each other) define a movement dimension in pairs, the ROM results as a restricted set of points. It should be noted that the range of motion sometimes depends on parameters of the moving or moved partner, as in the case of the shoulder joint or the hip joint, where the lateral abduction of the shoulder joint or the (lateral) abduction of the hip joint strongly depends on the rotation of the moving bone (humerus or femur) due to a hard-elastic (joint geometry) and firm-elastic (ligamentous) limit of motion. See also the corresponding explorations:
Abduction of the arm in rotation and abduction of the leg without rotation.

A distinction must be made between the passive range of motion, which can be achieved by an examiner and which a joint allows until one of the possible limits of motion stops it, and the active range of motion, which is actually covered by action of the muscles covering the joint. A distinction is made between the following movement limits:

• soft-elastic: a limit of movement set by a muscle. The movement limit is perceived as soft and with an increasing stretching sensation while movement towards the limit. The stretching sensation can cover the entire range (0 to 10) of the NAS. In addition to this muscle that is currently limiting the movement, one of its synergists can also set a soft-elastic limit after that of the first has been displaced. In this case, the ROM can be increased by improving the flexibility of the muscles.
• firm-elastic: a limit defined by a ligament. In this case, no muscle stretched during movement sets a soft-elastic boundary and a bony boundary is not (yet) present. This is often the case with ankle joints.
• hard-elastic: a limit set by a bone, or more precisely: the cartilage of the articulating bones. Such a limit is found in most people in the elbow joint, for example, in standard anatomical position in the direction of extension of the elbow joint. If the arm flexors are sufficiently flexible, neither a firm-elastic (ligamentous) nor a soft-elastic (muscular) limit of movement exists before the hard-elastic limit of movement.

The difference between the active and passive range of motion becomes quite clear in the example of the knee joint: the active flexion of the knee joint by muscles of the hamstrings is limited by active insufficiency or, in the case of poor flexibility of the monoarticular parts of the quadriceps (or dependent on the position of the hip joint even the biarticular rectus femoris), even earlier by passive insufficiency, i.e. by a lack of flexibility of their antagonistic quadriceps. This difference should not be confused with the limits set by parts of the active musculoskeletal system (soft-elastic) or the passive musculoskeletal system (firm-elastic, hard-elastic).

The active or passive ROM can be specified in angular degrees (°) or, in the case of movements, for example for training purposes, as a percentage (%) of the possible contraction of a muscle to be trained, in which case the specification ultimately refers to the interval of the sarcomere lengths. Typically, the ROM is a convex set.