ФИЗИОЛОГИЯ ЧЕЛОВЕКА, 2009, том 35, № 5, с. 62-70
УДК 612.821
BEHAVIOR OF DOMINANT AND NON DOMINANT ARMS DURING BALLISTIC PROTRACTIVE TARGET-DIRECTED MOVEMENTS
© 2009 A. Zuoza*, A. Skurvydas*, D. Mickeviciene*, B. Gutnik**, D. Zouzene*, B. Penchev**, S. Pencheva**
* Lithuanian State Academy of Physical Education, Kaunas, Lithuania ** Unitec Institute of Technology, Auckland, New Zealand Received September 18, 2008
The purpose of this study is to investigate the asymmetry of dominant and non-dominant arms regarding reaction time (RT), velocity, force and power generated during ballistic target-directed movements. Fifty six, right-handed young males performed protractile movements with both arms separately by pushing a joystick towards a target-line as quickly and as accurately as possible. Participants performed 21 repetitions with each hand. The temporal, spatial, kinetic and kinematic parameters were computed. All movements were grouped regarding their accuracy (when joystick fell short, stopped precisely or overreached the target). Each group of movements was analyzed separately and the data obtained was compared across groups. The results showed that although the left arm was less accurate than the right one, it reached the target significantly faster, developing greater average force and power. The forces of acceleration and deceleration of the left arm were greater too. We did not observe a significant lateral difference in RT in situations when the arm fell short of the target, or stopped precisely on the target. It was only when the target was overreached that the left arm displayed a significantly greater RT than the right one. We explain the results from the asymmetry of motor behavior in favor of the influence of both hemispheres in this process.
In daily life we come across many tasks that require us to reach and displace objects. A number of studies have demonstrated that the dominant right arm of healthy adults has been faster [1, 2], more accurate [3, 4] and with fewer variables [2, 5] than the non-dominant left arm.
Very often kinematical analysis has been used to explain movement abnormalities in patients with left or right hemisphere damage. During these studies some lateral differences have been observed in healthy right-handed subjects, usually taken from a control group [613]. However these control groups comprised a relatively small number of participants; the age and gender range was limited, and the degree of handedness was not precisely specified.
The kinetic aspects of rapid target-directed movements corresponding to handedness remain largely undetermined [14]. Our research did not identify literature on lateral differences of some kinematic (velocities) and kinetic (force and power) characteristics of rapid doing well and failed target-directed movements performed by large groups of healthy young adults, with narrow age diapason and with intact brain. Thus the specific aim of our work was to analyze some kinetic parameters during protractile target-directed movements performed by dominant and non dominant arms in the situations when the target was or was not successfully achieved.
METHOD
Fifty six healthy right-handed male subjects 18 to 20 years old participated in our experiment, after completing the ethic protocol. The degree of right-handedness was examined following the method recommended for this type of experiment by Sainburg and Kalakanis [15] and was confirmed by laterality level of >+80 on the 10-point Edinburgh Inventory [16]. All subjects had normal or corrected-to-normal visual acuity and had no significant neurological history. The left and right arms were tested in separate sessions on the same day. The arm tested first was alternated across subjects.
In order to determine the energy and power of protraction of the arm during the target-directed movements, it was necessary to determine the mass of the arm. Body height and mass were measured using a standard method of measurement [17]. Using regression equations [18], we calculated the mass of the upper limb segments: arm (M upper arm), forearm (M forearm) and hand (M hand). To increase the accuracy of the calculations we used additional regression equations recommended by Hall [19]. The total mass of the arm (M total) was calculated as:
M total arm = M upper arm + M forearm + M hand
The latest certified model of "Analyzer of dynamic parameters of human movement" (patent number 5251, 2005-08-25, Lithuania) was used for the experiment. The set-up consisted of a computer monitor on a table with an armchair in front of it. Two vertically oriented joysticks (one for each hand) were placed on the table
in front of the monitor. A "target" (a line parallel to the front edge of the table) was situated 30 cm directly in front of the joysticks. A standard position of joysticks and the target was maintained strictly permanent throughout the experiment. The joysticks could be moved by the participants, but not the target. Only one hand was to be used at a time. There was an electronically based monitoring system which was constantly registering and recording the distance between joysticks and the target, the onset of each movement, the maximal speed of protraction, the time period for achievement of this speed, and the total time of protraction.
Participants sat in the armchair in front of the monitor and focused on a white dot in its centre. In the initial position the joystick was held so that the shoulder and forearm were at an angle of 90 degrees (see figure). Subjects were instructed to move the joystick forward until it reached the target, thus performing a linear protractile movement.
Movements were not initiated unless a command for that was issued. The command was organized in the following way: the beginning of each movement was indicated by a blinking of the white dot, which acted as a visual "Get ready" signal. Shortly afterwards it was followed by a "Go" signal represented by a sudden disappearance of the dot from the screen and the simultaneous appearance of the target. The start-signal pattern appeared at random intervals (2-6 seconds) as recommended by Green et al.[20]; Hummel et al. [21].
Each participant was also instructed that once the "Go" command had been given he had to try to reach the target with the joystick producing a single protractile movement with a linear trajectory as quickly and as accurately as possible. Each participant was also fully aware that, once the protraction of his arm was over, corrections of its final position were not to be performed.
All participants had to undergo a brief preliminary training in accordance with the above mentioned protocol before the initiation of the experiment.
Movement initiation and termination were determined by analyzing the joystick's velocity profile as seen in Flash and Hogan [22] and Sainburg and Kala-kanis [15]. Twenty-one movements with each hand were performed by every participant. To avoid the influence of a possible preparatory stress-factor at the beginning, and a fatigue-factor by the end of the experiment, the first three and the last three movements were not included in the final analysis.
The final position was defined as when the joystick had fully stopped. Each movement occurred within a prescribed short period of time (400-600 ms) as recommended by Sainburg and Kalakanis [15].
A movement was considered to be successful when three conditions were satisfied: the joystick had achieved a velocity of more than 50 cm/s; the cursor was placed within a range of 1.5 cm in front to 1.5 cm past the target-line; the movement duration was not longer than one second.
C
D
The Experimental design with "Analyzer of dynamic parameters of human movement."
A Participant sits in the armchair in front of the monitor and focused on a white dot in its centre. (A) The beginning of each movement is indicated by a blinking of the white dot, which acted as a visual "Get ready" signal. (B) Shortly afterwards it was followed by a "Go" signal represented by a sudden disappearance of the dot from the screen and the simultaneous appearance of the line- target (C). A "target" (a line parallel to the front edge of the table) is situated 30 cm directly in front of the joysticks. Small black square represents the initial position of the Joystick (D). In the initial position the joystick is held so that the shoulder and forearm were at an angle of 90 degrees. Subjects should move the joystick forward until it reached the target, thus performing a linear protractile movement with a linear trajectory as quickly and as accurately as possible. The linear trajectory of movement (on the D) was appeared on the screen immediately after each repetition.
Primary analysis of data from the main experimental protocol
The Registered parameters: maximal speed (Vmax), expressed in m/s; distance of total motion from the initial to the final position (dtotal) expressed in meters; the moment of the appearance of the visual stimulus "Go" (the moment of target presentation on the screen) T0; the moment when the speed of the joystick achieves 0.005 m/s (beginning of protraction of arm) - Tbegin protract; the moment when the joystick achieves maximal acceleration Tacc; the moment when the joystick achieves the maximal speed T vmax; the moment when the speed of the joystick drops to 0 m/s (end of protraction of arm) - Tprotract.
Computed parameters: reaction time (RT) was defined as the interval between the appearance of the target on the screen and the moment when the joystick had achieved speed equal 0.005 m/s (RT = Tbegin protract -T0); the total period of acceleration, or the period for achievement of the maximal velocity - (t acctotal); the period of deceleration, i.e. the interval between the maximal joystick's velocity to a speed of 0 m/sec at the completion of the movement; the average speed of motion Vav; the average kinetic energy of motion of the arm, (E kin total a
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