George Tzetzis

A dynamical systems investigation of lower extremity coordination during running over obstacles

OBJECTIVE To investigate intralimb coordination during running over a level surface and over obstacles of three different heights. DESIGN The phasing relationships between the foot and leg motions in the frontal plane, and the shank and thigh motions in the sagittal plane were used to compare patterns of coordination. BACKGROUND The coordinated actions of lower extremity segments are necessary to absorb the impact forces generated during running. The behavioral patterns of these segments can be studied under changing task demands using analysis techniques from the Dynamical Systems Theory. METHODS Ten subjects ran at their self-selected pace under four conditions: over a level surface and over obstacles of different heights (5%, 10%, 15% of their standing height). A force platform was used to record impact forces during landing after obstacle clearance, while kinematics were collected using a two-camera system. RESULTS The increases in obstacle height resulted in significant changes in impact forces (34% increase between the two extreme conditions) and more in-phase relationships between the segments during early stance. No changes were observed in the variability of the phasing relationships. CONCLUSIONS The coordination changes observed might be compensatory strategies aimed to reduce forces and potential injury. However, since the impact forces still increased significantly, it is also possible that the observed changes might be at-risk movement patterns predisposing runners to injury.

Experience with Perceptual and Motor Skills in Rhythmic Gymnastics

Based on the notion of measuring motor performance, an experiment with three groups of 20 elite rhythmic gymnasts (N = 60), 9 to 10 yr., 11 to 12 yr., and 13 to 15 years of age (national level), with children of the same size and age was conducted, to identify the important abilities for the achievement of excellence in this sport. Motor abilities (whole-body coordination, dynamic balance, static balance, sense of kinesthesis, whole-body movement time, and eye-hand coordination) as well as perceptual abilities (whole-body reaction time, anticipation of coincidence, and depth perception) were compared. Analysis showed that scores on measures of whole-body coordination, dynamic balance, and static balance were higher for elite groups of athletes than for corresponding control groups. Moreover, elite athletes in the oldest group scored higher than those in the youngest group on anticipation of coincidence, on eye-hand coordination, and on static balance. These findings indicate the presence of systematic differences between elite athletes and nonathletes on motor abilities related to experience in this sport.

Modeling in Learning Two Volleyball Skills

The present study was designed to investigate the influence of two different types of modeling and knowledge of performance on acquisition and retention of two volleyball skills (set and serve). Participants were 63 boys and 53 girls in elementary school, whose mean age was 11.7 yr. (SD = .5). The children were randomly assigned into two groups given the same practice method for 16 practice sessions (8 for the set and 8 for the serve) but different types of modeling. Some participants observed a videotape of an expert model performing the skills, and the second group observed a videotaped replay of their own performance. Verbal cues were provided simultaneously with the videotaped demonstration. The first group improved set and serve skills more on acquisition and on the retention test than the second group. This improvement was present when scores and form were evaluated. Modeling plus instructional cues seemed to improve childrens learning of two volleyball skills (set and serve), and this procedure is suggested for use by practitioners.

Comparison of performance for winning and losing beach volleyball teams on different court dimensions.

The purpose of this study was to investigate and compare the performance between winning and losing teams in Beach Volleyball (BV) matches on courts of new (8x8m) and old dimensions (9x9m) at the side out phase. Side out in BV means the change of the right to serve Nine semifinals and seven finals of the Hellenic BV Championship taking place at an 8x8m and 9x9m court were video-recorded using a camera. 34 sets and 1466 phases were recorded and the following technical skills were analyzed: a) serve b) reception c) attack. In addition, attack was divided into two categories according to the type of the attack: a) spikes and b) shots. The term effectiveness was established by the ratio determining the total kills minus total errors divided by total attempts. Independent samples t-test was used in order to compare the above mentioned parameters between the winning (N) and losing (H) teams at these two different court dimensions (8x8, 9x9). Significant differences were found, t(16) = 3.06, p< .01), in the attack efficiency (MN8x8 = .476, SD = .086, MH8x8 = .315, SD = .131), (t(18) = 2.44, p< .05), in the spike efficiency (MN8x8 = .479, SD = .162, MH8x8 = .254, SD = .236), in the percentage of errors (MN8x8 = .139, SD = .052, MH8x8 = .204, SD = .077), (t(18) = 2.21, p< .05), in the percentage of receptions errors (MN9x9 = .09, SD = .043, MH9x9= .032, SD = .029), t(10) = 2.73, p< .05) and in reception (MH9x9 = 0.96, SD = 0.03, MH9x9 = 0.90, SD = 0.05), (t(10) = 2.74, p< 0.05). Winning and losing teams used the spikes and shots at approximately the same rate. In conclusion, different skills performance contributed to winning the match after the reduction in court dimensions. On the 8x8, the winners had better attack efficiency and fewer errors, while on the 9x9 they had better reception.

CURRICULUM ENRICHMENT WITH SELF-TESTING ACTIVITIES IN DEVELOPMENT OF FUNDAMENTAL MOVEMENT SKILLS OF FIRST-GRADE CHILDREN IN GREECE

The purpose of this study was to investigate the effect of Self-testing activities on the development of fundamental movement skills in first-grade children in Greece. Two groups of children were tested. The Control group (n = 23 children) received the regular 12-wk. physical education school program and the Experimental group (n = 22 children) received a 12-wk. skill-oriented program with an increasing allotment of self-testing activities. The Test of Gross Motor Development was used to assess fundamental movement skills, while the content areas of physical education courses were estimated with an assessment protocol, based on the interval recording system called the Academic Learning Time-Physical Education. A 2 × 2 repeated measures analysis of variance with group as the between factor and testing time (pretest vs posttest) as the repeated-measures factor was performed to assess differences between the two groups. A significant interaction of group with testing time was found for the Test of Gross Motor Development total score, with the Experimental group scoring higher then the Control group. A significant main effect was also found for test but not for group. This study provides evidence supporting the notion that a balanced allotment of the self-testing and game activities beyond the usual curriculum increases the fundamental motor-skill development of children. Also, it stresses the necessity for content and performance standards for the fundamental motor skills in educational programs. Finally, it seems that the Test of Gross Motor Development is a useful tool for the assessment of childrens fundamental movement skills.

Three Feedback Methods in Acquisition and Retention of Badminton Skills

Comparison of three different feedback methods using information about the correct execution of the technique, errors of execution, and a combination of these on the acquisition and retention of two badminton skills of different difficulty were examined. Participants were 48 young male athletes, 10 to 14 years of age, with 2 to 4 years of training. They were divided into three equal groups and instructed on the long forehand serve, a more difficult serve than the short backhand. The first group received instructions for correct execution, the second group received instructional cues on errors of execution, and the third group received instructions on errors and how to correct them. The training program lasted 12 practice units. There was a pretest, a posttest after the end of the 10-wk. training program, and 2 wk. later, a retention test. A three-way (2 difficulty × 3 groups × 3 measures) analysis of variance with repeated measures on the last factor was applied to analyze scores with the three practice methods of corrective feedback for the two badminton skills. Analysis showed the group receiving correct technique information had increased scores on both skills. The group receiving information on errors increased their scores on the less difficult skill. The group receiving information on errors and correct technique increased their scores on the more difficult skill. Physical education teachers or coaches teaching skills to young participants should consider difficulty of skills and use appropriate corrective feedback for better acquisition and retention of sport skills.

The Relation of Goal Orientations to Physical Activity in Physical Education

Researchers support the relationship of task orientation with exerted effort, persistence and self-reported physical activity but there is little evidence on the relation of goal perspectives with objective measures of physical activity. The purpose of this study was to examine behavioural correlates of goal orientations using an objective measure of physical activity in physical education (PE). The participants of the study were 112 students,boys and girls, of different age groups 9–10 and 11–12 years ofage. A field test was conducted and objective measures of physical activity(CSA) and goal orientation were obtained in 16 PE lessons. ANOVA analysis revealed that there was no significant difference in sex or age, or time participation in moderate physical activity time but there was a significant difference in participation in vigorous activities. Students that scored higher in task orientation had a longer participation in vigorous activity regardless of their ego orientation comparing them with those who had high egoand low task. These results may provide significant insights for appropriate practice in PE.

ASSESSMENT OF ABILITIES IN BASKETBALL: A PRELIMINARY STUDY '

Understanding the responding at two competitive levels of sports is prerequisite for successful identification and selection of the best athletes. The present study is a preliminary report about scores on 17 cognitive, perceptual, motor, and psychological measures of 13 elite Greek basketball athletes (national team), 20 to 22 years of age, and 15 children on a national basketball team and 14 to 15 years of age. Longitudinal studies must be conducted for the identification of the relationships among these measures and basketball performance and the development of a model for selection of athletes.

GOAL SETTING AND FEEDBACK FOR THE DEVELOPMENT OF INSTRUCTIONAL STRATEGIES

This study was done to evaluate the effectiveness of three practice methods, (a) feedback as knowledge of performance (KP), (b) feedback as knowledge of results combined with the goal-setting method, and (c) a combination of knowledge of performance and results with the goal-setting method on the performance and learning of basketball skills of different complexity. Three groups (n = 26) of children followed the practice methods and the performance (result), and technique of simple and complex basketball skills (dribble, pass, shoot, and lay-up) were assessed for their effectiveness. Subjects practiced using four exercises for each skill, three times a week, for eight weeks. A performance and a retention test (two weeks later) were conducted. A multivariate analysis of variance with repeated measures on the last factor indicated that knowledge of performance with results of goal-setting significantly improved the techniques of the more complex skills but it was significantly better than the knowledge of results and goal-setting method for passing. Giving knowledge of results and setting goals improved performance and proved to be better than the knowledge of performance method. Finally, the combined method was as good as the knowledge of performance and as good as the knowledge of results plus goal setting in performance but improvement was delayed mostly for the more complex skills. Attentional needs for the analysis of information given determined the success in skills execution and the effectiveness of the methods. The different content of the information given to the athletes may improve different aspects of motion or execution of the skills.

Styles of Managing Team Conflict in Professional Sports: The Case of Greece

Coaches as leaders of sports teams should identify the causes of conflict between the athletes and handle conflict effectively. The aim of this study was to examine the methods and ways coaches use to handle conflict in professional teams in Greece. The sample consisted of 42 professional football‐soccer, basketball and volley ball coaches, which were surveyed using questionnaires. Using the descriptive statistics and the one‐way Analysis of Variance (ANOVA), it was found that: a) coaches are using five styles in order to manage conflict, and b) the most effective styles that can resolve team conflicts are the collaborating style, the compromising style and the avoiding style and the least effective styles from those suggested are the competing style and the accommodating style.