František Vaverka

Association between body height and serve speed in elite tennis players

The purpose of this study was to determine the association between the body height (BH) of elite tennis players and their serve speeds: SF (fastest serve in a match), S1 (average speed of the first serve in a match), and S2 (average speed of the second serve in a match). Data were collected from the worlds best tennis players who participated in all four Grand Slam tournaments in 2008 (men, n = 78–84, BH = 1.85 ± 0.07 m; women, n = 70–78, BH = 1.73 ± 0.07 m). Statistically significant correlations (r) between BH and serve speed were found in all 24 statistical analyses (p < 0.01). The correlation coefficients were similar in men and women. The correlation coefficients of BH with SF and S1 ranged 0.48–0.64 for men and 0.48–0.59 for women. The correlations between BH and S2 were weaker and more variable (r = 0.20–0.50 for men and 0.24–0.42 for women). The BH of the men explained 27%, 30%, and 14% of the variance of SF, S1, and S2, respectively, with corresponding values for female players of 27%, 27%, and 12%.

The influence of an additional load on time and force changes in the ground reaction force during the countermovement vertical jump.

Abstract The aim of this study was to determine how an additional load influences the force-vs-time relationship of the countermovement vertical jump (CMVJ). The participants that took part in the experiment were 18 male university students who played sport recreationally, including regular games of volleyball. They were asked to perform a CMVJ without involving the arms under four conditions: without and with additional loads of 10%, 20%, and 30% of their body weight (BW). The vertical component of the ground reaction force (GRF) was measured by a force plate. The GRF was used to calculate the durations of the preparatory, braking, and acceleration phases, the total duration of the jump, force impulses during the braking and acceleration phases, average forces during the braking and acceleration phases, and the maximum force of impact at landing. Results were evaluated using repeated-measures ANOVA. Increasing the additional load prolonged both the braking and acceleration phases of the jump, with statistically significant changes in the duration of the acceleration phase found for an additional load of 20% BW. The magnitude of the force systematically and significantly increased with the additional load. The force impulse during the acceleration phase did not differ significantly between jumps performed with loads of 20% and 30% BW. The results suggest that the optimal additional load for developing explosive strength in vertical jumping ranges from 20% to 30% of BW, with this value varying between individual subjects.

Validity of Mechanical Power Output Measurement at Bench Press Exercise

Validity of Mechanical Power Output Measurement at Bench Press Exercise In sport training and rehabilitation practice, it is usual to use methods of mechanical muscle power output measurement, which are based mainly on indirect force measurement. The aim of this study was to verify the validity of indirect measurement for mechanical muscle power output with bench press exercise. As a criterion of validity, we selected a combination of kinematic and dynamic analyses. Ten men participated in this study. Average age of tested subjects was 28.0 ± 3.4 years. At mechanical power output measurement, these subjects lifted at maximum possible speed loads of 18, 26.5, 39.2 and 47.7 kg. Validity of mechanical power output measurement by means of a method using indirect force measurement was estimated using Spearmens Correlation Coefficient. Factual significance of differences in average values of power output, force and velocity, measured by a method using indirect force measurement, in comparison to the selected criterion, was evaluated by means of effect of size. Power output measurement method using indirect force measurement showed lower values of force in relation to the criterion in the whole scope of selected loads. Velocity values in the whole scope of selected loads did not show any significant difference between the criterion and the verified method. The mechanical muscle power output measured by the method using indirect force measurement is lower in relation to the criterion, especially in the low scope of loads, where also validity rate was low (R = 0.5).

Quantitative assessment of the serve speed in tennis

Abstract A method is presented for assessing the serve speeds of tennis players based on their body height. The research involved a sample of top world players (221 males and 215 females) who participated in the Grand Slam tournaments in 2008 and 2012. The method is based on the linear regression analysis of the association between the player’s body height and the serve speed (fastest serve, average first-serve, and second-serve speed). The coefficient of serve speed (CSS) was calculated as the quotient of the measured and the theoretical value of the serve speed on a regression line relative to the player’s body height. The CSS of >1, 1 and <1 indicate above-average, average, and below-average serve speeds, respectively, relative to the top world tennis players with the same body height. The CSS adds a new element to the already existing statistics about a tennis match, and provides additional information about the performance of tennis players. The CSS can be utilised e.g. for setting the target serve speed of a given player to achieve based on his/her body height, choosing the most appropriate match strategy against a particular player, and a long-term monitoring of the effectiveness of training focused on the serve speed.

Effect of an Arm Swing on Countermovement Vertical Jump Performance in Elite Volleyball Players

Abstract The aim of this study was to determine how elite volleyball players employed the arm swing (AS) to enhance their jump performance. The study assessed how the AS influenced the duration and magnitude of the vertical ground reaction force (VGRF) during the main phases (preparatory, braking and accelerating) of the countermovement vertical jump (CMVJ), the starting position of the body at the beginning of the accelerating phase and the moment when the AS began contributing to increasing the jump height. Eighteen elite volleyball players performed three CMVJs with and without an AS. Kinetics and kinematics data were collected using two Kistler force plates and the C-motion system. The time and force variables were evaluated based on the VGRF, and the position of the body and the trajectory of the arm movement were determined using kinematic analysis. The AS improved the CMVJ by increasing the jump height by 38% relative to jumping without an AS. The AS significantly shortened the braking phase and prolonged the accelerating phase, however, it did not influence the preparatory phase or the overall jump duration. The AS also significantly increased the average force during the accelerating phase as well as the accelerating impulse. The AS upward began at 76% into the overall jump duration. The AS did not influence the body position at the beginning of the accelerating phase. These findings can be used to improve performance of the CMVJ with the AS and in teaching beginning volleyball players proper jumping technique.

Association between serve speed and court surface in tennis

ABSTRACT The aim of the study was to determine whether the serve speed differs between Grand Slam tournaments (GSTs) played on different court surfaces. The study was carried out for both men and women (n = 70–98) who participated in four of the GSTs in 2008, 2012 and 2016 (Australian Open, French Open, Wimbledon and US Open). The following serve-speed parameters were obtained from the official GST websites: the speed of the fastest serve (FS), the average speed of the first serve in a given match (S1) and the average speed of the second serve in a given match (S2). Statistical analysis was performed using a mixed linear model procedure (NCSS 2007, Keysville, UT). FS varied irregularly, but it did not differ significantly between GSTs in the three observed years. The values of S1 and S2 for both men and women were highest in WIM in all three years, and were significantly higher than the other variables measured at the other GSTs. An association between serve speed and tennis court surface was confirmed only for S1 and S2 at fast grass court surfaces at WIM in the period 2008–2016.