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Author Harel Arzi; Tal Krasovsky; Moshe Pritsch; Dario G. Liebermann
Title Movement control in patients with shoulder instability: a comparison between patients after open surgery and nonoperated patients Type Journal Article
Year 2014 Publication Journal of Shoulder and Elbow Surgery Abbreviated Journal
Volume 23 Issue 7 Pages 982–992
Keywords Smoothness; kinesthesis; arm kinematics; shoulder instability; open surgery
Abstract (up) Background

Open surgery to correct shoulder instability is deemed to facilitate recovery of static and dynamic motor functions. Postoperative assessments focus primarily on static outcomes (e.g., repositioning accuracy). We introduce kinematic measures of arm smoothness to assess shoulder patients after open surgery and compare them with nonoperated patients. Performance among both groups of patients was hypothesized to differ. Postsurgery patients were expected to match healthy controls.


All participants performed pointing movements with the affected/dominant arm fully extended at fast, preferred, and slow speeds (36 trials per subject). Kinematic data were collected (100 Hz, 3 seconds), and mixed-design analyses of variance (group, speed) were performed with movement time, movement amplitude, acceleration time, and model-observed similarities as dependent variables. Nonparametric tests were performed for number of velocity peaks.


Nonoperated and postsurgery patients showed similarities at preferred and faster movement speeds but not at slower speed. Postsurgery patients were closer to maximally smoothed motion and differed from healthy controls mainly during slow arm movements (closer to maximal smoothness, larger movement amplitude, shorter movement time, and lower number of peaks; i.e., less movement fragmentation).


Arm kinematic analyses suggest that open surgery stabilizes the shoulder but does not necessarily restore normal movement quality. Patients with recurrent anterior shoulder instability (RASI) seem to implement a “safe” but nonadaptive mode of action whereby preplanned stereotypical movements may be executed without depending on feedback. Rehabilitation of RASI patients should focus on restoring feedback-based movement control. Clinical assessment of RASI patients should include higher order kinematic descriptors.
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Author Liebermann, D.G.; Krasovsky, T.; Berman, S.
Title Planning maximally smooth hand movements constrained to nonplanar workspaces Type Journal Article
Year 2008 Publication Journal of Motor Behavior Abbreviated Journal J Mot Behav
Volume 40 Issue 6 Pages 516-531
Keywords Adaptation, Physiological; Adult; Algorithms; Female; Hand/*physiology; Humans; *Intention; Kinesthesis/*physiology; Male; Models, Statistical; Movement/*physiology; Psychomotor Performance/*physiology; Reference Values; Writing
Abstract (up) The article characterizes hand paths and speed profiles for movements performed in a nonplanar, 2-dimensional workspace (a hemisphere of constant curvature). The authors assessed endpoint kinematics (i.e., paths and speeds) under the minimum-jerk model assumptions and calculated minimal amplitude paths (geodesics) and the corresponding speed profiles. The authors also calculated hand speeds using the 2/3 power law. They then compared modeled results with the empirical observations. In all, 10 participants moved their hands forward and backward from a common starting position toward 3 targets located within a hemispheric workspace of small or large curvature. Comparisons of modeled observed differences using 2-way RM-ANOVAs showed that movement direction had no clear influence on hand kinetics (p < .05). Workspace curvature affected the hand paths, which seldom followed geodesic lines. Constraining the paths to different curvatures did not affect the hand speed profiles. Minimum-jerk speed profiles closely matched the observations and were superior to those predicted by 2/3 power law (p < .001). The authors conclude that speed and path cannot be unambiguously linked under the minimum-jerk assumption when individuals move the hand in a nonplanar 2-dimensional workspace. In such a case, the hands do not follow geodesic paths, but they preserve the speed profile, regardless of the geometric features of the workspace.
Address Department of Physical Therapy, The Stanley Steyer School of Health Professions, Sackler Faculty of Medicine, Tel Aviv University, Israel. dlieberm@post.tau.ac.il
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ISSN 0022-2895 ISBN Medium
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Notes PMID:18980905 Approved no
Call Number Serial 33
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