Understanding the control strategies that underlie multijoint limb movements is important to researchers in motor control, robotics, and medicine. Due to dynamic interactions between limb segments, choosing appropriate muscle activations for initiating multijoint arm movements is a complex problem, and the rules by which the nervous system makes such choices are not yet understood. The aim of the dissertation studies was to evaluate some proposed initiation rules based on their ability to correctly predict which shoulder and elbow muscles initiated planar, two-joint arm movements in various directions. Kinematic and electromyographic data were collected from thirteen subjects during pointing movements involving shoulder and elbow rotations in the horizontal plane. One of the rules tested, which is based on statics, predicted that the initial muscle activity at each joint is chosen such that the hand exerts an initial force in the direction of the target, while another rule, based on dynamics, predicted initial muscle activity such that the initial acceleration of the hand is directed toward the target. For both rules, the data contradict the predicted initial shoulder muscle activity for certain movement directions. Moreover, the effects of added inertial loads predicted by the latter rule were not observed when a 1.8 kg mass was added to the limb. The results indicated, however, that empirically derived rules, based on ψ, the target direction relative to the distal segment, could predict which muscles would be chosen to initiate movement in a given direction. Furthermore, the relative timing and magnitude of initial muscle activity at the shoulder and elbow varied systematically with ψ. Thus, the target direction relative to the forearm may be an important variable in determining initial muscle activations for multijoint arm movements. These findings suggest a control scheme for movement initiation in which simple rules suffice to launch the hand in the approximate direction of the target by first specifying a basic motor output pattern, then modulating the relative timing and magnitude of that pattern.

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Thesis (MHSc--Health Science) -- AUT University, 2008. / Includes bibliographical references. Also held in print (xv, 121 leaves : col. ill. ; 30 cm.) in the Archive at the City Campus (T 612.76 MON)

Thesis (MHSc--Health Science) -- Auckland University of Technology, 2004. / Also held in print (80 leaves, 30 cm.) in Akoranga Theses Collection (T 612.75 ROT)

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An experiment was performed to evaluate the relations between active range of motion (ROM) and upper limb anthropometric dimensions. Eight anthropometric dimensions, forearm length, distal and proximal forearm circumferences, wrist breadth, wrist thickness, wrist circumference, hand breadth, and hand length in combination with gender, wrist position, and direction of motion or exertion were evaluated to determine their effects on instant center of rotation (ICOR) and the magnitude of force exertion. The knowledge gained from analysis of the study data will be the first step in the formulation of a biomechanical model of wrist flexion and extension. Such a model would predict forces and torques at specific wrist postures and be employed to reduce cumulative trauma disorders of the wrist. Sixty right-hand dominant subjects (30 male, 30 female) between 20 and 30 years of age all reporting no prior wrist injury and good to excellent overall physical condition, were employed in this study. The upper limb anthropometric dimensions and ROM were measured and recorded for each subject. The anthropometric dimensions were compared to tabulated data. The measured active ROM values were compared with values in the literature. Correlation coefficients between pairs of anthropometric variables (by gender) were calculated. The mean active ROM measures, 164.0 deg for females and 151.8 deg for males, were significantly different (<i>Z</i> = 2.193, <i>p</i> = 0.014). The relationships between the anthropometric variables and active ROM were analyzed by three methods: correlation between ROM and each anthropometric dimension, prediction (regression) equations, and analysis of variance (ANOVA). No correlation coefficient between ROM and any anthropometric dimension was greater than 0.7. No prediction equation, based upon linear and quadratic combinations of anthropometric dimensions variables, was above the threshold of acceptability (<i>R²</i> ≥ 0.5). The results of the ANOVA showed a significant effect for gender. The ICOR had been hypothesized to be either in the head or neck of the capitate. The Method of Reuleaux was employed to locate the leOR points for flexion and extension (over the ROM) of the wrist with three load conditions, i.e., no-load, palmar resistance, and dorsal resistance. Analysis of the data, using ANOYA, showed that wrist position was the only significant variable. Thus, in future wrist models, the assumption cannot be made that the wrist is a pin-centered joint for flexion and extension. The static maximal voluntary contractile forces that can be generated by recruiting only the six wrist-dedicated muscles in various wrist positions were measured. There was a significant gender difference for the mean flexion force (<i>Z</i> = 4.00, <i>p</i> = 0.0001) and for the mean extension force (<i>Z</i> = 4.58, <i>p</i> = 0.0001). Females averaged 76.3 percent of the mean male flexion force and 72.4 percent for extension. The force data, categorized by gender, were then analyzed using three methods: correlation of variable pairs, regression equations, and ANOVA. None of the eight anthropometric dimensions and ROM was correlated with flexion or with extension force at an acceptable level. The prediction equations, linear and quadratic combinations of all possible subsets of anthropometric dimension values, ROM, and wrist position did not meet the minimum acceptable level of <i>R²</i> ≥ 0.5. The ANOVA procedure showed gender, wrist position, direction of force exertion, and the wrist position interaction with direction to have significant effects upon maximal force exertion. / Ph. D.

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Master of Science / Most studies of condylar movement are based on the movement of an arbitrary condylar point. As the condyle is a 3-dimensional body which undergoes complex rotations and translations in function, the movement of one point in the vicinity of the condyle may not accurately represent condylar movement. The aims of this investigation were to determine in human subjects, during open-close and excursive jaw movements, the movement patterns of arbitrary and anatomical condylar points; and whether the trajectory of a single selected point can accurately reflect the movement of the condyle. In 44 subjects, condylar point movements were recorded with an opto-electronic tracking system (JAWS3D), which recoded the position of three light-emitting diodes attached to each dental arch. The primary point, selected to represent movement of the condyle, was 15 mm medial to the palpated lateral condylar pole, parallel to the Frankfort horizontal plane. Additionally, four points were selected along orthogonal axes in the sagittal plane, and four in the horizontal plane: each was 5 mm from the primary point. In two subjects, the mandibular condyles were imaged by computerised tomography (CT) and the lateral and medial poles, most superior, anterior and posterior points of their condyles were selected. The trajectories of each point were compared for each subject for the mandibular movements listed above. Variability in both path form and dimension was noted between the subjects for all mandibular movements. For example, in an open-close mandibular movement the condylar point translation varied in the antero-posterior direction between 1.8-22.8 mm, and in the supero-inferior direction between 4.5-12.1 mm. For each subject, the pathway of each point was different in form and dimension from that subject’s other condylar points for the open-close, and ipsilateral lateral mandibular movements. For the open-close movement, in only four of the 44 subjects were the arbitrary point traces similar in form within a subject; and the tracings of each subject’s condylar points showed, on average, a 3.2 mm difference in maximal horizontal (i.e. antero-posterior) translation and 2.9 mm in maximal vertical (i.e. supereo-inferior) translation. For contralateral lateral mandibular movements, the path form and dimension in the sagittal plane of the condylar points were similar within a subject; however the lateral component showed variability in path length for the different points within a subject. The pathways of the condylar points for a protrusive movement displayed the most similarity within a subject, with an average of 0.4 mm variation in maximal horizontal or vertical displacement between each subject’s arbitrary condylar points’ tracings. The anatomical condylar points of the two subjects showed variability between and within each subject. For these two subjects the trajectories of the arbitrary condylar points moved in directions similar to the anatomical points of all movements except for the ipsilateral lateral mandibular movement, where in one subject, the arbitrary condylar points moved posteriorly, inferiorly and laterally whereas the anatomical points moved anteriorly, inferiorly and laterally. There is much variability in both form and dimension for mandibular condylar movement between human subjects. There is also considerable variability within subjects in the form and dimension of condylar point movement, whether arbitrary or anatomical, depending on the point selected. By inference therefore, a single condylar point cannot accurately reflect the movement of the mandibular condyle, except perhaps for a protrusive mandibular movement. Multiple mandibular points are therefore required to describe the motion of the condyle. In an ipsilateral lateral mandibular movement, for example, an arbitrary point may move in a completely different direction to the mandibular condyle, and so anatomically derived condylar points should be utilised to assess accurately condylar movement.

The purpose of this study was to characterize glenohumeral joint laxity and stiffness using instrumented arthrometry. To evaluate the validity of an instrumented measurement system we compared cutaneous and bone-pinned measures of laxity and stiffness that replicate previously reported in vivo methodology. Characterization of capsular laxity was achieved through determination of the sagittal plane translational area at increasing levels of quantified force. Finally, a method for increasing the objectivity of the standard manual laxity examination was developed for the orthopaedic clinician to quantify humeral head translation and capsular volume in vivo. We hypothesized that: 1) cutaneous measures could accurately predict bone-pinned measures, 2) capsular laxity would increase with increasing levels of applied force, and 3) manual cutaneous, manual bone-pinned, and force-displacement bone-pinned measures of translation would be equal. Thirty fresh frozen cadaveric shoulder specimens (mean age=70��14 years) were tested. The shoulders were thawed and mounted to a custom-made shoulder-testing apparatus. Displacement was measured using an electromagnetic tracking system. Sensors were secured cutaneously and with bone-pins to the scapula and humerus. Force-displacement testing was performed using a load applicator and manual displacement testing utilized the anterior/posterior drawer and inferior sulcus tests. A comparison of cutaneous and bone-pinned measures of laxity and stiffness revealed good to excellent criterion validity (r=0.68 to 0.79). Examination of displacement measures at increasing levels of force revealed increasing capsular laxity with symmetric directional compliance. No significant difference was observed between anterior and posterior translation (0.4 mm, p=.55), with significant differences between inferior and anterior (4.6 mm, p<.0001) and between inferior and posterior (5.1 mm, p<.0001). A comparison of manual cutaneous to bone-pinned manual and kinetic measures of translation revealed a significant difference between methods (p=.0024) and between directions (p<.0001) with no significant interaction (p=.0948). Estimations of the force required to achieve clinical end-point suggest that greater force is required in the anterior (173 N) direction compared to posterior (123 N) and inferior (121 N). We have developed two new methods to measure glenohumeral joint kinematics and reported new information regarding normal kinematics of the glenohumeral joint. / Graduation date: 2001