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Table 3 Anatomical coordinate systems used for the kinematic analysis.

From: Three-dimensional kinematic analysis of the pectoral girdle during upside-down locomotion of two-toed sloths (Choloepus didactylus, Linné 1758)

Joint/element (hierarchy)

Anatomical meaning of rotation about axis

Zero-point for rotations

Global coordinate system (top)

   x-axis

-

-

   y-axis

-

-

   z-axis

-

-

1st thoracic vertebra (1st order)

   x-axis

Long axis rotation of vertebral column (roll)

Aligned to global x

   y-axis

Lateral undulation of vertebral column (yaw, +: undulation to the right)

Aligned to global y

   z-axis

Pitch of vertebral column (+: decrease of head-support distance)

Aligned to global z

Scapular center of rotation/scapula (2nd order)

   x-axis

Inward (+) /outward (-) rotation about long axis of scapula

Scapula is not rotated (long axis of scapula parallel to thoracic y-axis)

   y-axis

Abduction (-) /adduction (+) of scapula (yaw)

Scapula is not abducted

   z-axis

Protraction (-) /retraction (+) of scapula (pitch)

Scapula is vertical (in perfect dorso-ventral orientation)

Glenohumeral joint/humerus (3rd order)

   x-axis

Long axis rotation of humerus (roll, +: outward rotation)

Humerus is not rotated (epicondyles aligned in frontal plane)

   y-axis

Humeral abduction (-) /adduction (+) from scapular plane (yaw)

Humerus is in scapular plane

   z-axis

Humeral protraction (-) /retraction (+) (flexion in glenohumeral joint, pitch)

Humerus is orientated vertical (long axis parallel to scapula long axis)

Sterno-clavicular joint/clavicle (2nd order)

   x-axis

Rotation about long axis of clavicle (+: caudal rotation)

The curvature of the clavicle is pointing ventral

   y-axis

Anterior (+) /posterior (-) displacement of acromio-clavicular joint relative to manubrium sterni

Clavicle is pointing lateral and forms 90° angle to long axis and y-axis of the 1st thoracic vertebra

   z-axis

Dorso (-) /ventral (+) displacements of acromio-clavicular joint relative to manubrium sterni

Clavicle is pointing lateral and forms 90° angle to long axis and y-axis of the 1st thoracic vertebra

  1. Right handed coordinate systems are used for each joint with the x-axis oriented along the long axis of the bone of interest, z-axis always oriented to represent the most distinct motion of this bone, and y-axis orthogonal to both other axes (see Fig. 2). The anatomical coordinate systems are placed directly where the motion takes place, i.e. in the joint, and are fixed to the proximally adjoining bone. This means that motion of the bone of interest is reported relative to the proximally adjoining bone. Motion of the 1st order hierarchy bone (1st thoracic vertebra) is reported relative to a global coordinate system with positive x in direction of movement, positive y towards dorso-ventral image intensifier (ventral to the animal), and positive z to animal's left. + = positive rotation about respective axis; - = negative rotation about respective axis.