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Biomedical subjects

V Hatzitaki

Publications and source records attributed to V Hatzitaki.

6 recordsLinked to original sources
PubMed2003

Role of perceptual and motor abilities in instep-kicking performance of young soccer players.

The present study made a dynamic analysis of the ground reaction forces developed on the supporting foot during instep kicking to investigate the relation between specific perceptual and motor abilities and the performance of this skill. 45 young soccer players (11-13 years of age) participated in a series of laboratory tests assessing simple, choice, and discrimination reaction time, sustained attention, depth perception, and sense of kinesthesis. Kicking performance measured by the amount of impulse (calculated as the integral of force) developed on the supporting foot during kicking. There was a significant correlation of the kicking impulse with choice reaction time (r = -.54) and attention reaction time (r = -.41). Stepwise regression analysis indicated that choice reaction time accounted for 29% of the variation in the anterior/posterior kicking impulse and 16.4% of the variation in the medio/lateral kicking impulse. The significant relation between kicking impulse and measures concerning speed of information processing suggests that processes associated with fast response selection may play an important role in instep-kicking performance. These findings can provide useful information for designing of training schemes and testing protocols.

Adolescent↗
PubMed2002

Perceptual-motor contributions to static and dynamic balance control in children.

The authors addressed balance control in children from the perspective of skill development and examined the relationship between specific perceptual and motor skills and static and dynamic balance performance. Fifty 11- to 13-year-old children performed a series of 1-legged balance tasks while standing on a force platform. Postural control was reflected in the maximum displacement of the center of mass in anterior-posterior and mediolateral directions. Simple visual, discrimination, and choice reaction times; sustained attention; visuomotor coordination; kinesthesis; and depth perception were also assessed in a series of perceptual and motor tests. The correlation analysis revealed that balancing under static conditions was strongly associated with the ability to perceive and process visual information, which is important for feedback-based control of balance. On the other hand, when greater task demands were imposed on the system under dynamic balancing conditions, the ability to respond to the destabilizing hip abductions-adductions in order to maintain equilibrium was associated with motor response speed, suggesting the use of a descending, feedforward control strategy. Therefore, like adults, 11- to 13-year-old children have the ability to select varying balance strategies (feedback, feedforward, or both), depending on the constraints of a particular task.

Child↗
PubMed2001

Effect of single-limb inertial loading on bilateral reaching: interlimb interactions.

This study employed the paradigm of asymmetric limb loading during bilateral arm reaching to examine the motor system's ability to independently organize the discrete movement of both upper limbs to equidistant targets when one of the limbs is loaded under specific timing constraints. The loading procedure involved attaching two different Velcro strapped weights to the right wrist, thus increasing the right arm's mass by 25% (1 kg) and 50% (2 kg). Movements were captured by a high-speed digital camera (240 Hz), while electromyographic (EMG) activity of selected elbow and shoulder muscles of both limbs was recorded (1,000 Hz) simultaneously. The results revealed that the mechanisms used by the system to compensate for unilateral limb loading were as follows: First, addition of an inertial load resulted in an increased movement time and concomitant decrease in peak velocity of both the upper arm and forearm of only the loaded limb and was scaled to the added weight. Second, for the EMG parameters, adjustments to the inertial load were primarily characterized by an increase in burst duration of all muscles, with load-specific changes in activity and onset time: the elbow antagonist (biceps) demonstrated a decrease in activity with the 50% load, and the elbow agonist (triceps) had an earlier onset with the 25% load. Concomitant adjustments on the unloaded limb consisted primarily of an increase in burst duration of the shoulder and elbow agonists (pectoralis and triceps), an earlier triceps onset solely with the 25% load, and a decrease in activity of the biceps solely with the 50% load. Third, with the exception of biceps activity, the amplitude of EMG activity was invariant across changes in load for both the loaded and unloaded limb. This lack of modulation in activity may have been related to the inability of performers to meet the time constraint of simultaneous bilateral limb arrival to the end targets. This inability can be the result of an active strategy selection process to safeguard the actions against interference or alternatively it could simply be a consequence of the biomechanical properties of the system in relation to task constraints. These issues are discussed in the light of the present findings and those of previous studies.

Adult↗
PubMed1998

Dynamic joint analysis as a method to document coordination disabilities associated with Parkinson's disease.

OBJECTIVE: The purpose of the present study was to introduce dynamic joint analysis and subsequent phase partitioning of the movement pattern as a method for investigating the force control deficits associated with Parkinson's disease. DESIGN: Pilot data were collected from four non-impaired individuals and four patients afflicted with Parkinson's disease while performing arm movements of different spatiotemporal features. BACKGROUND: Investigation of motor performance in Parkinson's patients has related the clinically observed symptoms to the ability to control muscular force. METHODS: Experimental movements were filmed using a high speed camera operating at 200 Hz. The mechanical power characteristics of the elbow and shoulder were determined by applying inverse dynamic solutions to the kinematic data. Movement was reflected in a series of goal-directed phases describing the functional role of muscle activity across the joint. RESULTS: The analysis revealed that Parkinson's disease impairs the ability of the muscles to produce the energy required for performing ballistic, segmental movements. Moreover, patients demonstrated greater difficulty in controlling a two-joint task as opposed to a single-joint one; this was reflected by additional phases of activity at the elbow. CONCLUSIONS: Slowness of movement is associated with the inappropriate scaling of the muscle force, as well as with the limited use of motion-dependent forces in accelerating distal segment movement.

Journal Article↗
PubMed1998

Bilateral reaching to asymmetrical targets: muscle and joint dynamic interlimb adaptations.

A combined analysis of time, electromyographic, and joint torque measures was used to explore the force control processes underlying the dissociation of arm reaching movements performed bilaterally to targets of varying amplitude. Limb movements appeared closely coupled at movement initiation, which was confirmed by a strong tendency of the agonist muscles to remain synchronized despite any interlimb asymmetry in final target distance. On the other hand, interlimb decoupling occurred later as a result of the difference in the antagonists' timing of activation between the limbs. The partitioning of the net joint torque revealed that muscle activity is regulated in response to the intersegmental dynamics of the limb. It is proposed that spatial decoupling of asymmetrical movements becomes possible through postinitiation feedback processes which regulate muscle recruitment phenomena.

Acceleration↗