Knowledge of anatomical structure can reveal which movements and positions are producible by the body. In studies of visual recognition of moving humans, Johansson (1973, p. 201) reasons that “The geometric structures of body motion patterns in man and higher animals are determined by the construction of their skeletons”; and in an early study of “dynamic anthropometry”:
Man exhibits some of his most distinctively human characteristics in his pattern of motion. The ease with which he spans distance and executes intricate maneuvers testifies to the harmony that exists between the construction of the body and its motor mission. (Elftman, 1955, p. 553)
Therefore it would be beneficial for an implicit knowledge of “biological constraints” to be included within systems for the visual recognition of body movements (Vaina and Bennour, 1985, p. 224).
Laban (1966) states that “The structure and function of the human body limits the number of movements which the human being can perform” (p. 16) and so movement “is produced by limbs of the body and is governed by their anatomical structure which permits only certain movements to be made” (p. 84). Laban’s choreutic conception poses that “The body itself, in its anatomical or crystalline structure, is built up according to the laws of dynamic crystallization” (p. 105) and so “In order to study harmony of movement we must consider the relations between the architecture of the human body and the spatial structure of the kinesphere. (p. 106).
IVA.71 Choreutic Deflections Arising From Anatomical Constraints.
The prototype/deflection hypothesis posits that inclinational directions occur in actual body movements as a result of anatomical constraints:
Of course these six [dimensional] directions are not performed directly in the vertical-, lateral- and sagittal-dimensions, since these are not practicable for our limbs because of their attachment to the body. In movement it is always a matter of diagonals and spirals. (Laban, 1926, p. 25)
It is the construction of the body which demands a modification of the purely cubic aspect of the directional scheme of the kinesphere, and alters slightly the emplacement of the twelve signal-points [ie. diametral loci] when the body moves. (Laban, 1966, p. 101)
Because of the differences in flexibility of the spine in different segments and the range of the joints of the limbs, the planes are rectangular [ie. icosahedral] and the pull of one of the dimensions in each plane is dominant over the other. (Bartenieff and Lewis, 1980, p. 32)
The structure of the body makes the performance of pure diagonal movements impossible although a skillful mover can give the impression of such movements which appear as extremes of ultimate flight and fall. . . .
. . . Because the body limits the fulfillment of perfect three-dimensional shapes that pure diagonals would offer, most three-dimensional shapes are created through modified diagonals [ie. icosahedral inclinations]. . . These are available to the body. (Bartenieff and Lewis, 1980, p. 33 [italics theirs])
. . . one-dimensional movements are always about to slip into two- or three-dimensional movements because of the three-dimensional potential of the ball and socket joints . . . The global structure of those joints causes subtle rotary adaptations to every change of direction and [in response] the torso will slightly shape itself for support. (Bartenieff and Lewis, 1980, p. 89)
IVA.72 Range of Articulation at Single Joints.
The “range” of movement is a basic anatomical constraint which specifies the space accessible for movement via articulations at single-joints or from multi-joint skeletal linkages. These have also been referred to as the “joint range” versus the “cumulative range of the end member” in ergonomic research (Dempster, 1955, pp. 568–570; see IIB.42). Laban (1966, pp. 106-107) called these the “‘zones’ of the limbs” in which “the body and its limbs can be moved only in certain restricted areas of the kinesphere” and their “super zones” through which “Every point of the kinesphere can be reached with any one limb”. The more joints which are contributing to the range of the distal end of the skeletal linkage, the greater its range will be.
Laban (1966, p. 106) explores the articulation ranges of single joints and compares these with the hypothesized icosahedral-shape of the kinesphere. The joint-range data is identified as coming from “Anatomists” who measured “a large number of people in ‘normal’ living conditions” and “measurements taken from lifeless human bodies”, but the actual source of this data is not cited. In ergonomic studies, Pheasant (1986, p. 145) points out that “There are surprisingly little joint range data available”, and in their kinesiology textbook Rasch and Burke (1978, p. 32) add that measures of ranges of motion “are remarkable for their lack of agreement”, most likely because of considerable differences between Subjects.
However, some measurements of single joint ranges are available which can be used to reevaluate Laban’s conclusions. The angular measure of joint ranges can be compared to the angles between dimensions and diameters in variously-shaped kinespheric nets (for detail about sizes of angles; see Appendix X). This comparison was conducted and a consistent relationship was not found between single-joint ranges and the angles between directions as posited by the deflection hypothesis (see Appendix XI). Some single-joint ranges correspond to cuboctahedral diameters, others correspond to the hypothesised organically deflected icosahedral diameters, while others correspond to dimensions.
This does not directly contradict the prototype/deflection hypothesis since determining the structure of the kinesphere from single-joint ranges has little ecologic validity. The vast majority of body movements in real environments do not consist of single-joint articulations. Rather, organic movement consists of coordination among collections of joints and skeletal links. These are described as “coordinated structures” in which kinematic chains of body-segments function as a group rather than individually (see IIIB.60). If the kinesphere has a particular structure it should be evident in observations of organic movements involving integrated, coordinated collections of joints and body-segments rather than individual joint articulations.
There is also no reason to believe that individual joints are articulated to their full range during organic movement. Indeed, one may expect that when possible the full range of joint movement would not be used because of the ecological advantage of maintaining some margin for error (for when you really need it). Other considerations are more likely to govern the structure of the kinesphere. For example, the directions and range of motion might be governed by the need to maintain equilibrium (see IIID.50), the creation of a meaningful communicative expression, the desired quality of the movement (eg. delicacy, forcefulness), or by the exterior spatial layout of a particular task (eg. locations of shelves around a workspace will effect the directions and size of movements).
An underlying factor within all of the examples given above which may govern the structure of the kinesphere is the desirability for the movement to achieve its goal in the most efficient way possible. This is “another important principle of body mechanics: the individual tends to function in the way that affords the greatest conservation of energy” (Rasch and Burke, 1978, p. 98). Laban (1966, p. 45) refers to this as “economy of effort” according to which “It is natural for all living organisms to use the simplest and easiest paths in space”. The ecological need for economy may be the greatest consideration which governs the structure of the kinesphere.
IVA.73 Oblique Joint Structure.
A brief review of anatomical joint structure reveals that the body tends to move in oblique orientations which do not lie within an egocentric Cartesian plane. Even at the most basic level the bones themselves are twisted so that adjacent joints in a skeletal linkage are slightly rotated with respect to one another (Dempster, 1955, pp. 569-570). This slight twist causes the two joints to articulate in different planes at a small oblique angle to one another.
A rod gripped in the hand and held by one’s side so that the rod is approximately sagittal, will actually be held at an oblique “grip angle”. This follows a direction downwards from the forearm (102° angle between the bar the central axis of the forearm) and slightly outwards (14° angle between the bar and the radial and ulnar styloid processes of the wrist) (Dempster et al., 1959, p. 290; mean of 40 men). This produces a sagittal deflection of the diagonal down-right-forward (for the right hand).
Because the head of the humerus is not a perfect sphere the articulation possibilities of the arm in the shoulder joint are not equal in all directions. The greatest elevation of the arm can be achieved in a forward and sideways-outward direction (Gray, 1977, p. 253). This is a vertical deflection (steep) of the diagonal up-right-forward (for the right arm).
At the elbow joint, the articulatory surface of the humerus (trochlea) with the ulna is oriented at an oblique angle to the lengthwise axis of the humerus. Because of this, when the elbow is extended and the forearm is supinated (palm forward) the forearm and the upper-arm do not lie in a straight line, but the lengthwise axis of the forearm is oriented at an oblique angle outward relative to the lengthwise axis of the upper-arm (‰13°). During flexion the forearm moves on an oblique path upwards and inwards towards the body’s medial plane (Gray, 1977, p. 257; Nordin and Frankel, 1989, p. 251).
Similarly, during knee articulation the tibia and femur do not remain in the same plane because of the orientation of their articulating surfaces. The femur is not oriented vertically but is tilted laterally outward at the top. During knee flexion the tibia does not remain in a paramedial plane. Instead, the path of the ankle moves obliquely outwards (relative to the femur) so that at full flexion the tibia and femur are oriented in the same plane (tilted outward at the top approximately 10° from the vertical). During knee extension the tibia retraces its path. The ankle travels obliquely inwards towards the midline so that at full extension the tibia is oriented near to the vertical dimension (Gray, 1977, p. 279).
The structure of the inner and outer condyles which comprise the articulatory surfaces of the femur with the tibia at the knee joint also take the tibia movement out of a paramedial plane. The inner condyle has a greater length than the outer condyle, and its surface is inclined obliquely outwards. Because of this, just before full extension of the knee the tibia will glide upward and outward over this oblique surface causing the lower leg to rotate outwards at the knee joint. The reverse action occurs during knee flexion with the lower leg rotating inwards (Gray, 1977, p. 279).
Vertebral facets push against each other during spinal articulations and so guide the “coupled motion” of lateral spinal flexion always occurring together with spinal rotation (Nordin and Frankel, 1989, p. 216; also Rasch and Burke, 1978, p. 226). This rotation causes lateral spinal flexion to always twist slightly out of the Cartesian frontal plane.
IVA.74 Oblique Muscular Lines-of-pull.
In addition to oblique directions produced by the structure of articulatory surfaces in skeletal joints, the attachments and orientations of muscles tend to create oblique paths rather than motion within a dimensionally oriented Cartesian plane. This is referred to as a muscle’s “line of pull” (Rasch and Burke, 1978, pp. 34, 117; Wells and Luttgens, 1976, pp. 37-38, 77). Even a cursory review of skeletal muscles reveals that their lines of pull are oriented at oblique angles to the body’s Cartesian planes. Dimensionally oriented movements are accomplished by the simultaneous contractions of separate muscles whose oblique lines of pull neutralise each other, thus producing a dimensionally oriented trajectory midway between the two obliques.
The majority of muscles acting on the spine and head* have a combined action of lateral flexion together with rotation (Rasch and Burke, 1978, pp. 231–237). When these muscles act on only one side of the spine-head their combined actions create oblique movement paths resulting from lateral flexion and rotation which pulls the movement out of the frontal plane. This rotation always accompanies lateral flexion of the spine even though it may not be overtly visible (Ibid, p. 226). When the abdominal muscles (viz. transversus, rectus, obliques) act independently they will also laterally flex and simultaneously rotate the torso (Gray, 1977, p. 365), thus producing the bending+rotation which creates an oblique downwards and crossways path.
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* Muscles acting on the spine and head include the multifidus; semispinalis thoracis and cervicis; iliocostalis lumborum, thoracis, and cervicis; longissimus thoracis, cervicis, and capitis; splenius cervicis and capitis; and the sternocleidomastoid.
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The pectoralis major simultaneously adducts, flexes, and inward-rotates the humerus (Gray 1977, p. 381). This follows the oblique direction down-forward-inward. When the latissimus dorsi acts upon the humerus it simultaneously adducts, extends, and inward-rotates it. Gray (1977, p. 341) points out that this oblique direction of humerus motion (down-back-inward) commonly occurs during a downward blow of the arm in fighting or in sabre practice.
The oblique orientations of the pectineus and the adductors brevis, longus and magnus causes these muscles to both adduct and outward-rotate the femur (Gray, 1977, p. 426). The outward rotation tends to pull the femur pathway out of the frontal plane during adduction. The gluteus maximus and the biceps femoris (one of the “hamstrings”) each extend and also outward-rotate the femur pulling it out of the paramedial plane during hip extension. The gluteus medius and minimus each abduct and also inward-rotate the femur pulling it out of the frontal plane during abduction (Gray, 1977, pp. 431-433).
This brief review of muscular actions shows that bodily actions in obliquely oriented planes are kinesiologically simpler than bodily actions in Cartesian dimensionally oriented planes. The independent action of most muscles produces body motion in oblique planes, whereas motion in Cartesian planes requires a higher degree of coordination in which two or more different muscles must cooperate and function as a higher-order system.