yogabook / movement physiology / rein system
Rein system
A rein system is a structure of partially antagonistic muscles that span the center of rotation of a joint on opposite sides so that they can serve both directions of a movement dimension. These can be individual muscles, as in exorotation in the knee (the biceps femoris), but are usually a group of muscles.
The term is primarily used for muscle systems that serve the lower-ranking of two dimensions of movement, i.e. the less pronounced ones in terms of range of motion, exertable force and relevance for everyday human movements, i.e. pronation/supination in the ankle joint, ulnar abduction/radial abduction in the wrist and internal rotation/external rotation of the lower leg in the knee joint. This can involve individual muscles, such as the biceps femoris for external rotation in the knee joint, but it is usually a group of muscles.
The most important rein systems are
- Reinsystem of the ankle joint
The ankle is stabilized and moved by the medial tibialis posterior and its lateral fibularis brevis antagonists with regard to the pronation-supination dimension of movement . In the standing leg, they stabilize and move voluntarily in the corresponding direction. If both reins are not in balance, this causes a change in the position and kinetics of the joint. In the free leg, they then cause an unwanted movement if no conscious countermeasures are taken. - Rein system of the knee joint
The knee joint is stabilized with regard to the rotation of the lower leg (internal rotation – external rotation) and moved medially by the inner hamstrings of semimembranosus and semitendinosus (and, secondary also the gracilis and sartorius) and laterally by the antagonist biceps femoris. - In a certain sense, the stirrup under the foot consisting of fibularis longus and tibialis anterior can also be described as a rein system, with both muscles attaching to the same bones: Os cuneiforme mediale, Os metatarsale I, except that the fibularis longus runs plantar from lateral to medial across the foot. They are exact antagonists in their two functions: fibularis longus: pronation and plantar flexion, tibialis anterior: supination and dorsiflexion.
- Rein system of the wrist
We also find a system of reins in the wrist: for radial abduction consisting of extensor carpi radialis longus, extensor carpi radialis brevis and flexor carpi radialis on the one hand and the extensor carpi ulnaris and flexor carpi ulnaris muscles for ulnar abduction on the other. Extensor carpi radialis longus (Crista supracondylaris lateralis) and extensor carpi ulnaris (Caput ulnare) do not origin in the corresponding epicondyles of the humerus and therefore cannot be affected by golfer’s elbow or tennis elbow.
In the standing leg, the ankle’s rein system stabilizes and moves in the corresponding direction at will. If the two reins are not in balance, this causes a change in the position and kinetics of the joint. In the free leg, they then cause an unwanted movement if no conscious countermeasures are taken.
In addition to the above-mentioned rein systems, the extrinsic muscles that move the thumb can also be included: flexor pollicis longus for radial abduction, abductor pollicis longus, extensor pollicis brevis (but not extensor pollicis longus due to a different attachment tendon) and extensor digiti minimi for ulnar abduction.
The term rein system is similar to the term muscle slings, which is not used uniformly; here, too, some authors refer to a set of (at least partially) antagonistic muscles. In the more sharply formulated of these sources, however, the term is more general than the term rein system, in which it refers to any muscles that move in both directions of an axis of movement.