Abstract
Background and Study Aim. Movement variability is one of the fundamental topics concerning the control of human movement. In recent years, researches have focused on various aspects of variability, which has changed the noise to useful variable on human movement. Present study investigated movement variability level in high skilled dart players that repeated throws over many years.
 Material and Methods. Seven experienced dart players (three women and four men) were threw 36 darts in three sets (each set 12 throws) from a standard distance (2.37 meters), while the kinematic features of the shoulder, elbow, and wrist were recorded during the throws. Qualisys motion capture system with six cameras was used to record the kinematics of the elbow.
 Results: entropy analysis revealed that greater variability in movement angle, velocity and acceleration resulted in better dart throwing performance but after reach to this level, throw variability was decreased. The remarkable point in these findings was that variability was constant across all samples despite the varied range of experience in throwing darts from 2.37 meters distance. Entropy analysis showed that in the throws of highly experienced individuals, variation led to greater throwing efficiency.
 Conclusions: these findings suggest that variability in a throwing activity, which revealed that moderate movement variability results in optimal throwing performance when dart throw has massive amount of practice during many years.
Highlights
Movement variability is considered as a regular change in human movement and can be defined as normal changes during repetitions of a motion [1]
Keywords: These findings suggest that variability in a throwing activity, which revealed that moderate movement variability results in optimal throwing performance when dart throw has massive amount of practice during many years. motor variability, dart throw, optimal performance, moderate variability, kinematics
Kinematic: Kinematics is a subfield of classical mechanics that describes the motion of points, bodies, and systems of bodies without considering the forces that cause them to move
Summary
Movement variability is considered as a regular change in human movement and can be defined as normal changes during repetitions of a motion [1]. If a darts player completes five dart throws from the same distance, none of the throws would be identical to one another as changes occur at different levels of the nervous system In this regard, movement variability has been investigated and reviewed based on three general perspectives. The uncontrolled manifold (UCM) hypothesis comprises the second major viewpoint regarding movement variability The basis of this hypothesis is the unlimited degrees of freedom and movement solutions in the nervous system, stating that the movement system always has excessive components and solutions that can solve any momentary problem in movement [3]. Findings from clinical trials indicate that movement disorders in certain diseases can increase the variability of movements In this case, increased variability is indicative of decreased performance quality [7]
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