yogabook / movement physiology / abduction (in general)

Abduction means moving away. In the yogabook, the term is not used for the shoulder joint without any further designation (there it is called frontal abduction or lateral abduction), but it is used for the hip joint for the lateral movement of the leg, as well as for the little and big fingers and toes (big toe: hallux and thumb: pollex). The conceptual opposite is used in the same place for moving towards the medial plane (in case of the leg and the arm), midline of the hand or midline of the foot. There are quite a few sources in the anatomical literature that use an insufficiently clear and semantically inconsistent nomenclature by correctly referring to the frontal abduction of the arm as „anteversion“, but only up to an angle of less than 90°. From 90° the movement is then called „elevation“. The lateral movement (lateral abduction) of the arm is called „abduction“, but again only up to an angle of less than 90°. After that, this movement is also called „elevation“. It is therefore not possible to differentiate between a frontal and a lateral 100° movement. Moreover, this movement („elevation of the arm“) from 90° is called the same as the cranial movement of the shoulder blade, the execution or omission of which is not necessary for a far lateral and frontal angle of the arm to the body axis. Only when the flexibility of the latissimus dorsi in particular is restricted is there any connection at all, namely in such a way that this muscle restricts the simultaneous elevation of the shoulder blade and frontal abduction or lateral abduction of the arm. This is because it spans the shoulder joint and the scapulothoracic sliding bearing (which is not a real joint).

It becomes a little more complicated, as the joint structure with the cranially laterally protruding acromion of the scapula necessitates an outward rotation (the caudal inferior angulus laterally) of the scapula so that the humeral head does not impinge at the acromion. Together with the ligamentous structure of the shoulder joint, this leads to its characteristic that lateral abduction is only possible up to a good 90° with a turned in arm. For further lateral abduction it must be turned out, so the degree of possible lateral abduction is a function of the angle of rotation. Similarly, and in the same sense, the ability to abduct (laterally) in the hip joint is a function of the rotation of the femur: abduction is only possible by a good 20° in a neutral rotational position, but if the leg is turned out far, lateral abduction is only limited much later and primarily by the hamstrings, which is then a soft-elastic movement limit in contrast to that without external rotation, which is firm-elastic or even hard-elastic.

These facts are too rarely mentioned in the general anatomical literature. However, it may be credited to the authors that these correlations are much clearer perceivable with very good flexibility of the test subjects, which is not uncommon among yoga performers, than with a sample from the average population.

Further points are worth mentioning: firstly, the upper arm’s ability to rotate becomes increasingly limited with increasing abduction to the lateral or frontal side, so that in the exact overhead position of the arm there are hardly any degrees left. Most of any apparent movement is likely to be protraction or retraction of the scapula. Secondly, very flexible subjects can abduct the arms both 180° frontally and 180° laterally, so that the limit of both movements is the same. If the two movements are carried out even further, the results naturally differ. For 185° lateral abduction, one could also speak of 180° frontal abduction plus 5° transverse adduction.

The fact that independent terms have been established in the nomenclature for lifting the leg forwards (flexion of the hip joint) and the arm (anteversion in the shoulder joint) forwards, i.e. into the field of vision, but not to the side, should be sufficiently justified by the typical human activities since time immemorial: most activities take place in the immediate field of vision, be it picking something up or putting it down, working on something, handing it over. In contrast, significant lateral abduction in the hip joint without external rotation is rarely found in everyday life and even combined with external rotation is more likely to occur in a sporting context or when climbing, for example. In the case of the shoulder joint, the situation is only slightly more favourable with lateral abduction, which would also always be avoided when handling heavier objects. After all, the design of the feet makes it easy to support the body forwards, but lateral support is only possible with external rotation of the leg and abduction in the hip joint, which means that objects are rarely passed to the side in most activities and are handled even less laterally.

It should also be noted that older literature still uses the term flexion for the frontal abduction in the shoulder joint and extension for the retroversion of the shoulder joint, which probably originated as an analogy to the hip joint.