I am a graduate student from Australia who, as a first experiment, needs
to document the biomechanics of certain shoulder muscles in order to
later use this information to help interpret EMG data from shoulder joint
movements (isometric and isotonic flexion/extension and
abduction/adduction) in subsequent experiments to follow.

The 3 muscles I am interested in are the pectoralis major, latissimus
dorsi and the deltoid. The data I would like from predetermined
(cadaveric) segments of these muscles are; the lines of action of each
intramuscular segment and the angle of the line of action from the
intended plane of movement, the moment arms and the axis of rotation
(ICR) of the glenohumeral joint for the ranges of movement utilised
(isotonic). Optimally, during the EMG experiments where miniature
surface electrodes are placed on the subject's segments I would like to
know the above information for each segment at any stage in the movement.
Also useful would be an indication of the force each segment was

Some of the questions I have been pondering over are;

1. Is there one easy way that all this information can be gathered
preferably in vivo. Have looked at MRI (Rugg et al, 1990) but am not sure
whether the shoulder is an applicable joint and whether the images for
the segments would be clear enough. Have also looked at articles by Van
Der Helm and colleagues 1991, 1992 and 1994 but have been advised that
spatially digitizing 3D in vivo is difficult.

2. Would cameras and markers on segment origin and insertion followed by
digitizing give adequate 3D representation along with the Reuleaux method
(1875) for the axis of rotation work?

3. Is the straight line approach in comparison to the centroid line
approach (Jenson and Davy, 1975) adequate for these muscles and hence the
moment arm determination for each segment of each muscle?

Comments on any of the issues mentioned would be greatly appreciated and
a list of responses will be posted in the usual manner.

James Wickham
Department of Biomedical Science
University of Wollongong
Northfields Avenue, Wollongong 2522
NSW, Australia

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