Vassilis Gerodimos

The acute effects of different whole-body vibration amplitudes and frequencies on flexibility and vertical jumping performance

Frequency and amplitude determine the training load of whole-body vibration (WBV) exercise and thereby possible neuromuscular adaptations. We investigated the effects of amplitude and frequency of a single bout of WBV on flexibility and squat jump performance (SJ) and the time-course of these effects. In the amplitude study, twenty-five females performed three vibration protocols (VPs) for 6 min at frequency of 25Hz and amplitudes of 4 mm, 6 mm, and 8 mm and one control protocol (CP). In the frequency study, eighteen females performed three VPs at 6mm amplitude and frequencies of 15 Hz, 20 Hz, and 30 Hz and one CP. Flexibility and SJ were measured before, immediately-post and 15 min recovery. All protocols were performed on a side-to-side alternating vibration plate. In the amplitude study, flexibility was improved (p<0.01) immediately-post in VP4, VP6, VP8 (31.8+/-8.2, 31.9+/-7.6, 31.5+/-7.9, respectively) and at 15 min recovery (31.6+/-8.1, 31.5+/-7.9, 31.0+/-8.2, respectively) vs. pre-vibration (30.2+/-8.6, 30.3+/-8.1, 30.2+/-8.3, respectively), but remained unchanged in CP (30.6+/-8.3 immediately-post, 30.7+/-8.2 at 15 min vs. 30.4+/-8.2 pre-vibration). In the frequency study, flexibility was improved (p<0.01) immediately-post in VP15, VP20, VP30 (31.5+/-5.2, 31.3+/-5, 31.7+/-5.3, respectively) and at 15 min recovery (31.3+/-5.4, 31.3+/-5.0, 31.3+/-5.3, respectively) vs. pre-vibration (30.6+/-5.4, 30.2+/-5.7, 30.3+/-5.9, respectively), but not in CP (30.7+/-5.1 immediately-post, 30.6+/-5 at 15 min vs. pre-vibration 30.5+/-5.7). There were no significant effects of amplitude or frequency on SJ. In conclusion, a single WBV bout using a side-to-side alternating vibration plate may increase flexibility which persists for at least 15 min, without altering jumping performance. These effects were observed irrespective of frequency and amplitude.

Reliability of Handgrip Strength Test in Basketball Players

Reliability of Handgrip Strength Test in Basketball Players Handgrip strength is important in basketball as various movements rely on the continuous use of wrist and digits flexor muscles when catching, holding, shooting and throwing the ball. Therefore, the assessment of handgrip strength is used in prepubertal, adolescent and adult basketball players. The reliability of handgrip strength may be influenced by several factors including age. The purpose of this study was to examine the reliability of handgrip strength in basketball players from childhood to adulthood. Male basketball players (n = 90) were assigned into three groups: prepubertal (9.8 ± 0.7yrs), adolescents (14.4 ± 0.6yrs), and adults (26.1 ± 5.6yrs). Each participant performed three maximal isometric contractions on each hand in two occasions, one day apart. Intraclass correlation coefficient (ICC), standard error of measurement (SEM) and 95% limits of agreement (LOA) were calculated. The test-retest reliability was high for both preferred (ICC = 0.94 - 0.98) and non-preferred (ICC = 0.96 - 0.98) hands, without differences in reliability among age-groups. The results showed a significant age-related increase (p < 0.05) in absolute and relative handgrip strength irrespective of hand preference. The present results indicate that maximum handgrip strength can be measured reliably, using the Jamar hand dynamometer, in basketball players from childhood to adulthood.

Exaggerated haemodynamic and neural responses to involuntary contractions induced by whole‐body vibration in normotensive obese versus lean women

What is the central question of this study? In obesity, the exaggerated blood pressure response to voluntary exercise is linked to hypertension, yet the mechanisms are not fully elucidated. We examined whether involuntary contractions elicit greater haemodynamic responses and altered neural control of blood pressure in normotensive obese versus lean women. What is the main finding and its importance? During involuntary contractions induced by whole‐body vibration, there were augmented blood pressure and spontaneous baroreflex responses in obese compared with lean women. This finding is suggestive of an overactive mechanoreflex in the exercise‐induced hypertensive response in obesity. Passive contractions did not elicit differential heart rate responses in obese compared with lean women, implying other mechanisms for the blunted heart rate response reported during voluntary exercise in obesity.

Acute and Chronic Whole-Body Vibration Exercise does not Induce Health-Promoting Effects on The Blood Profile

Abstract Whole-body vibration (WBV) exercise is an alternative, popular and easy exercise that can be followed by general public. Therefore, the aim of the present study was to investigate the influence of acute and chronic WBV exercise on health-related parameters. Twenty-eight women were allocated into a control group (n=11, mean ±SEM: age, 43.5 ±1.5 yr; body mass, 66.1 ±3.1 kg; height, 160.6 ±1.5 cm) and a vibration group (n=17, mean ±SEM: age, 44.0 ±1.0 yr; body mass, 67.1 ±2.2 kg; height, 162.5 ±1.5 cm). After baseline assessments, participants of the experimental group performed WBV training 3 times/week for 8 weeks. Before and after the chronic WBV exercise, the participants of the vibration group performed one session of acute WBV exercise. Blood chemistry measurements (hematology, creatine kinase, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, C-reactive protein, glucose, insulin, triacylglycerols, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, apolipoprotein A1, apolipoprotein B and lipoprotein, thiobarbituric-acid reactive substances, protein carbonyls, total antioxidant capacity, uric acid, albumin and bilirubin) were assessed pre-exercise and post-exercise at the first and eighth week of WBV exercise in both control and vibration groups. The results failed to support any effect of both acute and chronic WBV exercise on biochemical health-related parameters. However, it seems that WBV exercise is a safe way of training without a negative impact on muscle and liver functionality.

Age-related differences in peak handgrip strength between wrestlers and nonathletes during the developmental years.

Abstract Gerodimos, V, Karatrantou, K, Dipla, K, Zafeiridis, A, Tsiakaras, N, and Sotiriadis, S. Age-related differences in peak handgrip strength between wrestlers and nonathletes during the developmental years. J Strength Cond Res 27(3): 616–623, 2013—This study examined the development of peak handgrip strength from childhood to adulthood in wrestlers (n = 122) and nonathlete controls (n = 122). The effect of hand preference on handgrip strength and the relationship of anthropometrical characteristics with handgrip strength in wrestlers and controls were also evaluated. Participants were assigned into age groups: children, young adolescents, late adolescents, and adults. Body height and mass, hand dimensions (length, span, and width), and absolute handgrip (in kilograms) were measured. Handgrip strength was similar in wrestlers and controls in the younger age groups (i.e., in children and young adolescents), whereas late adolescent and adult wrestlers exhibited significantly greater peak handgrip strength (p < 0.05) than their control peers. Nonathletes older than 15 years demonstrated an approximately 10% greater peak handgrip strength (p < 0.05) with their preferred hand compared with the nonpreferred hand. In contrast, late adolescent and adult wrestlers exhibited similar handgrip strength with both hands. Peak handgrip strength exhibited a significant linear correlation with all the anthropometric measures examined; however, a higher percentage in the variation in peak handgrip strength was explained by body height and hand length than the other anthropometric variables in both groups. In conclusion, wrestlers exhibit a sport-specific pattern of handgrip strength changes during the developmental years. Body height and hand length exhibited the strongest correlations with handgrip strength during the developmental years in wrestlers and in controls. The training adaptations of wrestling resulted in symmetrical handgrip strength development in both hands at late adolescence and adulthood. These data serve to provide a descriptive profile of handgrip strength in wrestlers, to assist both coaches and health professionals for talent selection and/or development of training programs for performance enhancement and rehabilitation.

Analysis and comparison of fast break in top level handball matches

The aim of this study was to describe an alternative approach in order to estimate the level of specific endurance (stamina) via video-analysis in handball athletes, which is required during the whole game. One thousand five hundred three (1503) attacks from 15 matches of 8 teams participating in the first division of the 2003 National Men’s Handball Championship were studied. For the analysis, all attacks were recorded and categorized based on the type of fast break. Furthermore, for each type of attack the outcome of the shot (goal, riposte, missed goal) and the offensive errors were recorded. All the fast break attempts (successful ones or not) were taken into consideration. The data analysis was conducted using Crosstabulation and chi-square tests. The results revealed that, during the first half, the 1st and 2nd wave were used in a percentage of 45,9% and 54,1%, respectively (p<0.05), although during the second half the percentage of each type was 63,3% and 36,7%, respectively (p<0.05). The third wave of fast break was not recorded. The number of successful attempts of fast break in the first half (77,1%) was greater than in the 2nd half (66,9%) (p<0.05). During the first half the frequency of the 1st wave (45,9%) was lower than that in the 2nd wave (54,1%) (p<0.05). However, during the second half the 1st wave’s frequency (63,3%) was greater compared to the 2nd wave’s (36,7%) (p<0.05). The form of analysis which was used to record, research and compare the frequency of appearance of fast break showed a reduction of fast break in the second half compared to the first half. There was also a significant difference between the two half times regarding the successful and unsuccessful fast breaks. The results may indicate some influence of training specificity and provide suggestions to coaches regarding the organisation of handball training drills that will possibly lead to an increase in explosive power.

Static and Dynamic Handgrip Strength Endurance: Test-Retest Reproducibility

PURPOSE This study investigated the reliability of static and dynamic handgrip strength endurance using different protocols and indicators for the assessment of strength endurance. METHODS Forty young, healthy men and women (age, 18-22 years) performed 2 handgrip strength endurance protocols: a static protocol (sustained submaximal contraction at 50% of maximal voluntary contraction) and a dynamic one (8, 10, and 12 maximal repetitions). The participants executed each protocol twice to assess the test-retest reproducibility. Total work and total time were used as indicators of strength endurance in the static protocol; the strength recorded at each maximal repetition, the percentage change, and fatigue index were used as indicators of strength endurance in the dynamic protocol. RESULTS The static protocol showed high reliability irrespective of sex and hand for total time and work. The 12-repetition dynamic protocol exhibited moderate-high reliability for repeated maximal repetitions and percentage change; the 8- and 10-repetition protocols demonstrated lower reliability irrespective of sex and hand. The fatigue index was not a reliable indicator for the assessment of dynamic handgrip endurance. CONCLUSIONS Static handgrip endurance can be measured reliably using the total time and total work as indicators of strength endurance. For the evaluation of dynamic handgrip endurance, the 12-repetition protocol is recommended, using the repeated maximal repetitions and percentage change as indicators of strength endurance. CLINICAL RELEVANCE Practitioners should consider the static (50% maximal voluntary contraction) and dynamic (12 repeated maximal repetitions) protocols as reliable for the assessment of handgrip strength endurance. The evaluation of static endurance in conjunction with dynamic endurance would provide more complete information about hand function.

The efficacy of vertical vs. horizontal plyometric training on speed, jumping performance and agility in soccer players

This study compared the efficacy of a vertical and horizontal plyometric training program on acceleration, speed, jumping performance, and agility in young soccer players during the in-season period. Thirty male soccer players (19.1 ± 5.8 years) were assigned into a horizontal plyometric, a vertical plyometric, or a control group. The horizontal plyometric group and vertical plyometric group participated in an eight-week training program that was performed one day/week (in conjunction with conventional soccer training) and consisted of horizontal (for the horizontal plyometric group) or vertical plyometric exercises (for the vertical plyometric group). Acceleration (10-m sprint), speed (30-m sprint), agility, and jumping performance (horizontal and vertical) were assessed prior and after the completion of plyometric training programs. Agility, 30-m sprint performance, and vertical jumping performance (p < 0.01) improved following the completion of training in both horizontal plyometric group and vertical plyometric group, whereas horizontal jumping performance improved only in horizontal plyometric group (p < 0.01). There were no significant effects on acceleration for both horizontal plyometric group and vertical plyometric group. Furthermore, no differences were observed between groups in all performance parameters. In control group, acceleration, speed, agility, and jumping performance remained stable throughout the study. To sum up, horizontal or vertical plyometric training programs, consisted of one session/week, may be used by coaches and fitness professionals as effective exercise modalities for preserving or improving jumping performance, acceleration, speed, and agility in young soccer players during the in-season period.

Reliability of concentric and eccentric strength of hip abductor and adductor muscles in young soccer players

The concentric and eccentric strength profile and muscular balance of the hip joint are important parameters for success in soccer. This study evaluated the reliability for the assessment of hip abduction and adduction isokinetic strength over a range of angular velocities (30 and 90°/s) and types of muscular actions (concentric and eccentric) in young soccer players. The reliability for the assessment of reciprocal (conventional and functional) and bilateral torque ratios was also examined. Fifteen male soccer players (15±1 years) performed two sessions, separated by three days. The testing protocol consisted of five maximal concentric and eccentric hip abductions and adductions of both legs at angular velocities of 30°/s and 90°/s. The peak torque was evaluated in young soccer players using an isokinetic dynamometer (Cybex Norm), and the reciprocal strength ratios (conventional and functional) and bilateral ratios (non-preferred to preferred leg ratios) were calculated. The test-retest reliability for the assessment of peak torque (ICC = 0.71-0.92) and of reciprocal muscle group ratios (ICC = 0.44-0.87) was found to be moderate to high. Bilateral torque ratios exhibited low to moderate reliability (ICC = 0.11-0.64). In conclusion, isokinetic strength of hip abductor and adductor muscles and the conventional and functional strength ratios can be reliably assessed in young soccer players, especially at low angular velocities. The assessment, however, of bilateral strength ratios for hip abductor/adductor muscles should be interpreted with more caution.

Can learning of basketball be enhanced through a web-based multimedia course? An experimental study

This study’s aim is the creation of a web-based multimedia course for Physical Education (PE) students’ familiarization with the teaching of basketball, and the evaluation of its use as a complementary tool to conventional instruction, in terms of learning effectiveness and student acceptance. The course includes multimedia learning material as well as interactive learning activities and quizzes on the cognitive components of basic basketball skills and on other basketball-related topics (history of the sport, referee’s signals, training aids, basketball court). The study involved 88 undergraduate students during one semester. They were randomly assigned to two groups: a group that used the web-based multimedia course and also attended a conventional face-to-face course on the teaching of basketball (N = 45), and another group that only attended the conventional face-to-face course (N = 43). A pretest/posttest research design was followed. For both groups basketball knowledge was measured at the beginning and at the end of the semester through written questionnaires. The responses of the students of the first group towards the web-based course were also assessed, at the end of the semester, through a written feedback questionnaire. Within both groups, significant increases in students’ basketball knowledge were found. However, the web-based multimedia course in combination with conventional face-to-face instruction was significantly more effective than conventional face-to-face instruction alone in increasing students’ cognitive learning regarding the sport of basketball, at the same time being well-accepted by the students. These findings support the effectiveness of blended learning for PE at higher education level as well as the acceptance of this mode of learning by PE students.