Biomedical subjects

G Mavromatis

Publications and source records attributed to G Mavromatis.

6 recordsLinked to original sources

PubMed2006

Effect of two different sized hand paddles on the front crawl stroke kinematics.

AIM: The purpose of the present study was to determine the effect of two different sized hand paddles on the three-dimensional underwater stroke pattern of front crawl swimming at a fixed stroke rate. METHODS: Nine male adolescent competitive freestyle swimmers participated in the study. Each subject swam a series of 25 m trials at a constant stroke rate, without and with hand paddles of two different cross sectional areas (small paddles: 116 cm(2), large paddles: 311 cm(2)). An acoustic metronome connected with a sound amplifier was used to help the subject keep the stroke rate constant. Stroke rate was calculated for each subject using the time for 3 complete right arm stroke cycles. The underwater motion of each subject's right arm was filmed using two S-VHS cameras, operating at 60 fields/s, which were located behind two underwater viewing windows. The spatial coordinates of selected points on the right arm and the hip were calculated using the DLT procedure with 30 control points and after the digital filtering of the raw data with a cut-off frequency of 6 Hz, the hand's linear displacements and velocities, as well as the mean swimming velocity, were calculated. Moreover, the displacement of the hip in the direction of propulsion, from the right hand's entry to the next entry of the same hand, was calculated in order to determine the stroke length. For the statistical treatment of the data the analysis of variance for dependent samples was used. RESULTS: The analysis of the data revealed that when hand paddles were worn, the stroke length (F(2,16)=10.329; P<0.05) and the mean swimming velocity (F(2),16=5.076; P<0.05) were significantly increased, while the temporal characteristics of the underwater stroke and the displacement of the hand were not significantly altered. On the other hand, the peak backward hand speeds during the insweep (F(2,16)=4.794; P<0.05) and the push phase (F(2,16)=5.827; P<0.05) were greatly reduced. These modifications were greater when large paddles were worn. CONCLUSIONS: From the results of the present study it was concluded that the movement pattern was not significantly modified when swimmers swam with hand paddles, at a constant stroke rate. However, large hand paddles caused a decrease in their hand velocities during the underwater stroke.

Adolescent↗

PubMed2004

Snatch lift kinematics and bar energetics in male adolescent and adult weightlifters.

AIM: The aim of the present study was compare linear kinematics and energy changes of the barbell, along with the angular kinematics of the leg movement during the snatch technique, between male adolescent and adult weightlifters. METHODS: Two S-VHS cameras operating at 60 fields per second recorded the heaviest lifts of 14 male adolescent and 9 adult top-level weightlifters under competitive conditions. The spatial co-ordinates of selected points on the body and the barbell were calculated using the direct linear transformation procedure. A low pass digital filter with 4 Hz cut-off frequency was used for the smoothing of raw co-ordinate data. The ''t''-test for independent samples was used for the statistical treatment of data. RESULTS: The results revealed that there were no significant differences between the adolescent and the adult weightlifters in the majority of the kinematic variables. However, adolescent weightlifters extended their knees significantly slower (t21 = 4.211, p < 0.05) during the 1st pull and their ankles during the 2nd pull (t21 = 2.440, p < 0.05) than the adult weightlifters did. Moreover, the average relative power output was significantly greater for the adult weightlifters during both the 1st (t21 = 2.303, p < 0.05) and the snd pull (t21 = 2.611, p < 0.05). CONCLUSION: These results indicate that the adolescent weightlifters were characterised from a high level of snatch technique and differentiated from the adults predominantly at the less powerful execution of the movement.

Adolescent↗

PubMed2001

Modifications of neuromuscular activity and improvement in performance of a novel motor skill.

The relationship between the modifications in the myoclectrical activity after practice and the performance enhancement was examined regarding a ballistic movement of the elbow. 41 subjects practiced a novel throwing skill, which involved the throw of a ball, performing elbows flexion. Surface electromyograms of four muscles in the elbow region were analyzed, aiming at identifying the changes in the timing and the intensity of muscle activation that may account for improved performance. A repeated-measures analysis of variance identified an improvement in performance scores after practice and a significant decrease in the EMG for the agonists and the primary antagonist. Moreover, a significant increase in the delay of the activity onset in the antagonists was observed after practice. The variations of the EMG for the biceps brachii and the anconeus were significantly elated to improvement in performance. It was concluded that the modifications in the electrical activity of those to muscles were primarily responsible for the physical alterations associated with improved performance.

Adult↗

PubMed2000

Three-dimensional kinematic analysis of the snatch of elite Greek weightlifters.

We investigated the linear kinematics and the change in energy of the barbell and the angular kinematics of the trunk and leg during the snatch technique of 12 elite male Greek weightlifters under competitive conditions after the new weight classification. Two S-VHS cameras operating at 60 Hz were used to record the lifts. The spatial coordinates of selected points were calculated using the direct linear transformation procedure; after digital filtering of the raw data, the angular displacements and angular velocities were calculated for the hip, knee and ankle joints. The following variables were also calculated for the barbell: vertical and horizontal displacement, vertical linear velocity and acceleration, external mechanical work and power output. The results revealed that all weightlifters flexed their knees during the transition phase, independently of their weight category. This indicates that the athletes use the elastic energy produced during the stretch-shortening cycle to enhance their performance. In nine athletes, we found that the barbell trajectory did not cross a vertical reference line that passed through the initial position of the barbell. The vertical linear velocity of the barbell was increased continuously from the beginning of the movement until the second maximum extension of the knee joint, with no notable dip being observed. Regarding the change in energy of the barbell, we found that the mechanical work for the vertical displacement of the barbell in the first pull was significantly greater than the mechanical work in the second pull. In contrast, the estimated average mechanical power output of the athletes during the vertical displacement of the barbell was significantly greater in the second pull than in the first pull. We conclude that the major elements of the snatch technique of elite Greek weightlifters have not been affected by the new weight classification.

Ankle Joint↗

PubMed1997

Contextual interference effects in learning novel motor skills.

The present study investigated the generalizability of contextual interference effects by extending previous laboratory and field research to novel movements controlled by different motor programs. 30 men and 33 women learned novel throwing and kicking tasks, practicing with blocked, serial, or random schedules. The subjects practiced the tasks four days a week for two weeks and then were given a postest. One week later subjects were given a retention test. Significant improvements in performance were found for all groups for both tasks; however, a significant effect for practice condition was found only for the throwing task during retention, for which the random practice schedule led to better learning than the blocked and the serial practice. These findings suggest that the blocked, serial, and random practice methods could be effectively used for tasks controlled by different motor programs but must be practiced in the same teaching session, without expecting one to be more effective in learning than any other.

Analysis of Variance↗

PubMed1997

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.

Adolescent↗