Can one angle be simply subtracted from another to determine range of motion in three-dimensional motion analysis?
ABSTRACT To determine the range of motion of a joint between an initial orientation and a final orientation, it is convenient to subtract initial joint angles from final joint angles, a method referred to as the vectorial approach. However, for three-dimensional movements, the vectorial approach is not mathematically correct. To determine the joint range of motion, the rotation matrix between the two orientations should be calculated, and angles describing the range of motion should be extracted from this matrix, a method referred to as the matrical approach. As the matrical approach is less straightforward to implement, it is of interest to identify situations in which the vectorial approach leads to insubstantial errors. In this study, the vectorial approach was compared to the matrical approach, and theoretical justification was given for situations in which the vectorial approach can reasonably be used. The main findings are that the vectorial approach can be used if (1) the motion is planar (Woltring HJ. 1994. 3-D attitude representation of human joints: a standardization proposal. J Biomech 27(12): 1399-1414), (2) the angles between the final and the initial orientation are small (Woltring HJ. 1991. Representation and calculation of 3-D joint movement. Hum Mov Sci 10(5): 603-616), (3) the angles between the initial orientation of the distal segment and the proximal segment are small and finally (4) when only one large angle occurs between the initial orientation of the distal segment and the proximal segment and the angle sequence is chosen in such a way that this large angle occurs on the first axis of rotation. These findings provide specific criteria to consider when choosing the angle sequence to use for movement analysis.
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ABSTRACT: The purpose of this study was to provide evidence on the fact that the observed decrease in EMG activity of the gastrocnemius medialis (GM) at pronounced knee flexed positions is not only due to GM insufficiency, by examining muscle fascicle lengths during maximal voluntary contractions at different positions. Twenty-two male long distance runners (body mass: 78.5+/-6.7 kg, height: 183+/-6 cm) participated in the study. The subjects performed isometric maximal voluntary plantar flexion contractions (MVC) of their left leg at six ankle-knee angle combinations. To examine the resultant ankle joint moments the kinematics of the left leg were recorded using a Vicon 624 system with 8 cameras operating at 120 Hz. The EMG activity of GM, gastrocnemius lateralis (GL), soleus (SOL) and tibialis anterior (TA) were measured using surface electromyography. Synchronously, fascicle length and pennation angle values of the GM were obtained at rest and at the plateau of the maximal plantar flexion using ultrasonography. The main findings were: (a) identifiable differences in fascicle length of the GM at rest do not necessarily imply that these differences would also exist during a maximal isometric plantar flexion contraction and (b) the EMG activity of the biarticular GM during the MVC decreased at a pronounced flexed knee-joint position (up to 110 degrees ) despite of no differences in GM fascicle length. It is suggested that the decrease in EMG activity of the GM at pronounced knee flexed positions is due to a critical force-length potential of all three muscles of the triceps surae.Journal of Biomechanics 02/2006; 39(10):1891-902. · 2.72 Impact Factor
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ABSTRACT: The complex skeletal deformations that accompany Idioapthic Scoliosis pose a challenge to the clinician to non-invasively discriminate Idiopathic Scoliosis patients from children with no pathology. Therefore, the focus of this study is to non-invasively evaluate the position and amplitude of displacement of the pelvis, shoulders and thorax during quiet standing of Idiopathic Scoliosis patients and control subjects. The quiet standing posture of 18 healthy adolescent females and 22 Idiopathic Scoliosis subjects was evaluated using an Optotrak 3020 position sensor over a period of 120 s, with 4 repeat trials. Outcome measures included the mean position, root mean square amplitude and range over the duration of 120 s trials for both linear and angular measures of the pelvis, thorax and shoulders. Appropriate sample times were chosen and evaluated for stability over the 120 s period, and between trial reliability was evaluated. There was a significant difference between groups for the mean position of the shoulder blade rotation in reference to the base of support and to the pelvis. The Idiopathic Scoliosis patients had a significantly larger root mean square amplitude of anterior-posterior displacement of the T1 and S1 spinous processes in reference to the base of support. There was no difference between the sample durations to estimate the mean position of the body segments, however the root mean square increased significantly. This study demonstrates that postural abnormalities are evident during quiet standing in Idiopathic Scoliosis patients.Clinical Biomechanics 07/2005; 20(5):483-90. · 1.87 Impact Factor
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ABSTRACT: The contribution of scapulothoracic and glenohumeral motion to overall shoulder motion remains difficult to determine. We sought to determine the exact ratio between these two motion components in order to better understand overall shoulder kinematics in asymptomatic individuals in unconstrained reaching. This study assessed shoulder motion using bone-fixed sensors to quantify scapulohumeral motion during unconstrained raising and lowering of the arm. Electromagnetic tracking devices rigidly fixed to bone pins recorded active scapular and humeral motion. We found a significant difference in the ratio of glenohumeral elevation to scapular upward rotation during arm raising (2.3) and lowering (2.7). Each degree of glenohumeral elevation yielded scapular upward rotation of 0.43 degrees (raising) compared with downward rotation of 0.37 degrees (lowering), across the motion arc. Until 125 degrees of glenohumeral elevation, the scapula internally rotated and then externally rotated with further elevation. Scapular upward rotation and posterior tilting progressively increased until maximal elevation. Scapulohumeral rhythm was greatest in the first increment of raising the arm and higher overall when lowering the arm. Understanding these data allows improved evaluation of potential motion abnormalities in patients with shoulder pathology and may improve treatment for restoration of normal shoulder motion.Journal of shoulder and elbow surgery / American Shoulder and Elbow Surgeons ... [et al.] 05/2009; 18(6):960-7. · 1.93 Impact Factor