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Throwing Performance and Test-Retest Reliability in Olympic Female Water Polo Players

Freeston, Jonathan1; Rooney, Kieron1; Smith, Stephen2; O'Meara, Damien2

Journal of Strength and Conditioning Research: August 2014 - Volume 28 - Issue 8 - p 2359–2365
doi: 10.1519/JSC.0000000000000419
Original Research
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Freeston, J, Rooney, K, Smith, S, and O'Meara, D. Throwing performance and test-retest reliability in Olympic female water polo players. J Strength Cond Res 28(8): 2359–2365, 2014—Shooting performance is critical to successful water polo performance, requiring high levels of speed and accuracy. However, shooting speed and accuracy performance of elite female water polo players has not been described in detail nor has the reliability of accuracy measures been reported. Consequently, the aim of this study was to describe shooting performance in elite female water polo players and compare the test-retest reliability of the currently available accuracy measures. Ten Olympic female water polo players were tested on 3 occasions before Olympic competition for maximal throwing speed and accuracy (total error and hit percentage) toward various target locations, with and without a goalkeeper (GK) present. The current participants (all Olympic athletes) achieved higher speeds (16.8 m·s−1), higher hit percentages (45.3%) of a 20-cm2 sniper net target, and lower errors (20.7 cm) than any other female water polo players investigated previously. Performance was similar across the different target locations; however, both speed (15.2 vs. 14.8 m·s−1; p ≤ 0.05) and accuracy (50.2 vs. 37.7%; p ≤ 0.05) were reduced in the presence of a GK. Speed and total error was similar across the 3 testing sessions; however, hit percentage was statistically significantly higher in the final session (58.8% vs. 40.4 and 36.4%). Maximal throwing speed showed high levels of test-retest reliability (0.96). Total error (intraclass correlation [ICC] = 0.79) had slightly greater reliability than hit percentage (ICC = 0.73) overall. Hit percentage (ICC = 0.82) showed slightly greater reliability than total error (ICC = 0.72) without a GK present, whereas total error (ICC = 0.79) showed much greater reliability than hit percentage (ICC = 0.34) when a GK was present. This study benchmarks the high degree of throwing speed and accuracy required at the Olympic level in female water polo players. Although resource intensive, total error is a reliable measure of accuracy that allows for the nature of error to be described in detail, providing a great level of insight into performance. Hit percentage, while easier to obtain, should only be used when a GK is not present and in situations where describing the nature of error does not add value to coaching practices.

1Exercise, Health, and Performance Faculty, The University of Sydney, Lidcombe, Australia; and

2New South Wales Institute of Sport, Sydney, Australia

Address correspondence to Jonathan Freeston, jonathan.freeston@sydney.edu.au.

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Introduction

Shooting toward goal is one of the most important skills for successful performance in water polo (21). The overhead throw is the most commonly used method and is used when shooting at goal both from the field (17) and during penalty shot situations (7). Consequently, a large amount of research has sought to determine factors that contribute to successful shooting (throwing) performance in water polo.

Shot success requires a large degree of both speed and accuracy. High throwing speed is advantageous because it reduces the amount of time the goalkeeper (GK) and other defenders have to block the shot, whereas a high degree of accuracy allows the ball to be thrown between defenders and increases the distance the GK has to move to block the shot. A speed-accuracy trade-off has been well established for the skill of throwing in cricket (11,12) and handball (19,20) players, such that the accuracy is optimized at approximately 75–80% of maximal throwing speed (MTS). Although many previous investigations have focused on factors that influence throwing speed in water polo, including biomechanics/technique (6–9,23), anthropometrics (10), jump height (15), fatigue (17,18), and strength training (5), few studies have explored factors that influence throwing accuracy in water polo. Furthermore, the relationship between throw speed and accuracy remains poorly understood in this population. Successful water polo teams have demonstrated higher shooting percentages, more shots on target, and fewer shots blocked than their less successful counterparts (2–4,21). Only 2 studies have measured and described shooting accuracy in water polo, investigating the influence of swimming on subsequent accuracy in elite junior males (17) and collegiate-level females (18), respectively. The throwing abilities of elite female water polo players have not been described in terms of both speed and accuracy.

In addition to the lack of research in this area, when accuracy was investigated, a relatively simplistic method of assessment was used such that accuracy was described in terms of a hit or a miss. Although this method is adequate for a general understanding of accuracy, it fails to describe the nature of the error incurred. Furthermore, and problematically, the reliability of this measure remains unknown. More recently, European handball studies have implemented a more advanced method of accuracy measurement (13,19,20), which allows accuracy to be described in terms of magnitude (distance), direction (vertical vs. horizontal), and type (bias vs. consistency). This information carries potential to greatly enhance our understanding of water polo shooting errors and their causal mechanism(s), as well as provide opportunities for the development of novel training methods to address specific throwing inaccuracies to improve game performance.

As a result of the foregoing, we conducted this study with the following aims: (a) to describe the shooting performance of elite-level female water polo players in terms of speed, as well as specific accuracy parameters of distance, direction, and type and (b) To determine the test-retest reliability of the currently available methods for assessing throwing performance in water polo.

This study was conducted with the view to establish benchmark performance measures of elite female water polo throwing capabilities to serve as a reference for coaches working with similar or junior water polo populations. Furthermore, the test-retest reliability was performed to inform coaches regarding the most appropriate methods for the assessment of throwing performance within this sporting population.

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Methods

Experimental Approach to the Problem

A descriptive repeated measures research design was used for this study. Throwing speed was measured through radar gun, and accuracy was measured through video analysis during 3 pre-Olympic training camps, each separated by 2 months. Testing was conducted within an indoor aquatic facility. During each session, throwing performance was assessed under a range of different conditions including with a GK and without a GK (FREE) present, as well as different target locations including top left and top right (with GK) and top left, top right, and top center (without GK). No specific familiarization session was provided to the athletes because throwing toward these targets are commonplace within typical water polo training sessions. Participants did not engage in any throwing-specific training interventions between the testing sessions.

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Subjects

Ten elite female water polo players (24.9 ± 0.9 years, 1.79 ± 0.2 m, and 79.3 ± 3.5 kg) from the Australian national water polo team took part in the study (10). Before taking part in the study, participants were made aware of the experimental procedures involved, and written consent was obtained. This study complied with the ethical guidelines laid down for human research by the Australian National Health and Medical Research Council and was approved by the Australian Institute of Sport Ethics Committee.

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Procedures

Warm-Up

Participants performed a general warm-up routine consisting of 5–10 minutes of light-to-moderate–intensity swimming followed by 10–15 minutes of throwing, progressing from low-to-high intensity. Participants were then assessed for MTS and throwing accuracy as outlined below.

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Maximal Throwing Speed Test

Participants were tested for maximum throwing speed using a method adapted from previous work (11,12). Testing was conducted at an indoor aquatic facility. Participants performed maximal throws from the 5-m line from the goal. Regulation size (∼66-cm circumference) and mass (425 g) water polo balls (Mikasa, Dudley Park, South Australia, Australia) were thrown toward the goal. A cordless speed radar gun (Jugs Corporation, Tualatin, OR, USA; 99% absolute agreement with 3-D motion analysis laboratory) was positioned behind the net. Participants were given no specific target at which to aim and were instructed to “throw as hard as possible toward the radar,” as they performed 3 throws at maximal intensity. No constraints were placed on participants in regard to throwing technique. The values were averaged across the 3 trials and reported the participant's average MTS.

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Throwing Accuracy Test

Participants then performed a throwing accuracy test consisting of a total of 25 throws under the instructions, “with each throw, try and hit the target.” Participants were allowed to choose the speed at which they threw to optimize accuracy; however, bounce shots were not permitted. The first 15 throws were performed without a GK (FREE), with 5 throws performed to each of the 3 different targets of a Sniper Accuracy Trainer (Sniper; D & J Sports, Inc., Dallas, TX, USA; top left, top center, and top right), in a randomized order. A further 10 throws were then performed with an Olympic-level GK in place, with 5 throws to each of the 2 different targets (top left and top right), again in a randomized order. Testing was completed in pairs to allow for scheduled recovery periods and to facilitate ball return to the shooter. Approximately 3–5 seconds of rest separated each throw within a set of 5 throws, and 20–30 seconds of rest separated each set. Approximately, 5 minutes of rest separated the FREE and GK conditions, allowing the second participant in the pair to complete their FREE shots while enabling the GK time to swim into position.

Actual speeds of each throw were measured with a speed radar gun (Jugs Corporation), aimed at the participant's release point; however, no feedback regarding the speed of each throw was provided to the participants. To record the point of impact of the ball in relation to the target, a video camera collecting at 50 Hz (Canon MV800i; Canon Inc., Sydney, Australia) was positioned directly behind and in line with the target at a distance of 30.0 m and height of 1.0 m, whereas another camera was positioned perpendicular to the target and in line with the goal plane at a distance of 8 m and at a height of 1.0 m.

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Data Processing

Video footage from the 2 cameras was imported into Swinger Pro (version 3.0; Websoft Technologies, Victoria, Australia). The footage from the 2 cameras was synchronized using the moment of impact between a thrown ball and the goal frame. For each throw, total error was defined as the distance between the center of the ball and the center of the target and was calculated at the time when the ball intersected the front plane of the goal as determined by the side-view camera. For shots that were saved by the GK, the center of the ball was digitized at the point the ball was saved. The field of view was calibrated using the measured distances between the 4 corners of the goal.

Throwing accuracy was measured using total error (E), absolute constant error (ACE), and variable error (VE) as described previously (14). Total error was decomposed into horizontal (X) and vertical (Y) errors. Errors were averaged for each set of 5 throws. Absolute constant error (a measure of bias) was defined as the distance between the typical throw (Centroid) and the target, with the typical throw defined as the average X and Y locations of the 5 throws in a set. Variable error (a measure of consistency) was defined as the average distance between each throw and the centroid, or typical throw. Hit percentage was calculated as the number of throws that had passed through the cut-out area of the sniper net target.

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Statistical Analyses

Data were assessed for normality using the Kolmogorov-Smirnov test. Repeated measures analyses of variance (ANOVAs) were used to determine target location and GK effects on speed and E. Subsequent repeated measures ANOVAs were then conducted on the secondary accuracy parameters of ACE, VE, X, and Y. Given its nonparametric nature, hit percentage was analyzed for target location and GK effects using the Kruskal-Wallis and Mann-Whitney U-tests, respectively. Time effects on speed and E were determined using repeated measures ANOVAs, with subsequent repeated measures ANOVAs conducted on ACE, VE, X, and Y. Time effects on hit percentage were determined using the Kruskal-Wallis test with pairwise comparisons conducted using the Mann-Whitney U-test. A T-Test was conducted on X and Y to determine the relative contribution to E. Pearson's correlation was conducted to determine the relationship between E and hit percentage. Calculations of intraclass correlations (ICCs) and SEM were conducted to determine test-retest reliability of the radar gun method (speed), as well as the total error and hit percentage methods (accuracy) in accordance with Weir (22). Overall reliability was assessed using accuracy data from all throws. Reliability during FREE and GK conditions was also assessed separately. Statistical analysis was conducted using SPSS version 20.0. Statistical significance was set a priori at p ≤ 0.05, with the Holm-Bonferroni adjustment applied when multiple tests were conducted to protect against type 1 errors.

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Results

Target Location Effects

The location of the target did not statistically significantly affect the throwing speed (F(2,144) = 1.612, p = 0.20, η2 = 0.022) or accuracy as defined by either total error (F(2,144) = 2.137, p = 0.12, η2 = 0.029) or hit percentage (χ2 [2, n = 150] = 0.84, p = 0.66; Figure 1, Table 1).

Figure 1

Figure 1

Table 1

Table 1

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Goalkeeper Effects

The presence of a GK led to a statistically significant reduction in throwing speed (F(2,144) = 6.146, p ≤ 0.05, η2 = 0.041) and accuracy as defined by hit percentage (z = −2.67, p ≤ 0.05); however, the presence of GK did not statistically significantly affect total error (F(2,144) = 1.209, p = 0.27, η2 = 0.008). Horizontal error was statistically significantly higher during the GK condition (F(2,144) = 6.522, p ≤ 0.05, η2 = 0.043).

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Direction and Type Differences

Overall, vertical error was statistically significantly greater than horizontal error (t(149) = −6.39, p < 0.01), whereas VE was statistically significantly greater than ACE (t(149) = −16.369, p < 0.01) (Figure 2).

Figure 2

Figure 2

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Time Effects

Throwing speed (F(2,98) = 0.855, p = 0.41, η2 = 0.017) and total error (F(2,98) = 2.215, p = 0.12, η2 = 0.044) did not change statistically significantly over the course of the 3 testing sessions; however, hit percentage was statistically significantly higher in session 3 compared with sessions 1 (z = −3.64, p < 0.01) and 2 (z = −3.76, p < 0.01; Table 2).

Table 2

Table 2

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Correlation

Pearson's r revealed a statistically significant strong negative correlation between hit percentage and total error (r = −0.71, n = 150, p < 0.01; Figure 3).

Figure 3

Figure 3

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Test-Retest Reliability

Maximal throwing speed demonstrated high ICC (ICC = 0.96, 95% confidence interval [CI] = 14.6–18.6, SEM = 0.2 m·s−1). The overall ICC was higher for total error (ICC = 0.79, 95% CI = 18.1–23.2, SEM = 1.9 cm) than for hit percentage (ICC = 0.73, 95% CI = 34.5–55.9, SEM = 9.0%). However, when ICCs were conducted on the FREE and GK conditions separately, hit percentage (ICC = 0.82, 95% CI = 38.2–62.2, SEM = 8.2%) demonstrated higher reliability than total error during the FREE condition (ICC = 0.72, 95% CI = 17.0–22.6, SEM = 2.4 cm), whereas total error (ICC = 0.79, 95% CI = 19.7–27.4, SEM = 2.9 cm) demonstrated higher reliability than hit percentage during the GK condition (ICC = 0.34, 95% CI = 26.4–51.8, SEM = 16.6%).

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Discussion

The average MTS of the elite female water polo players in this study was 16.6 m·s−1, when averaged across the 3 sessions. These values are higher than any other reported throwing data collected in training for elite Spanish (15.7 m·s−1) (1), Greek (15.5 m·s−1) (16), or Australian (14.7 m·s−1) (7) women or sub-elite women (11.6 m·s−1) (18). The current participants also demonstrated high levels of accuracy, shooting at a hit percentage of 45.3%, and averaging 20.7 cm in total error. This is superior to hit percentages among collegiate-level females (30%; 18) and junior elite male water polo players (40%; 17). We attribute this superior throwing ability to the elite nature of the participants (all Olympic level).

Throwing speed and accuracy (E and hit percentage) was similar across each of the target locations (top left, top center, and top right); however, the presence of a GK had a negative effect on speed, hit percentage, and horizontal error. We present 2 possible mechanisms for this finding. First, the throwing technique used in the presence of a GK was statistically significantly different to that used during the FREE condition. Specifically, the GK condition simulated field shooting because participants were permitted to baulk repeatedly to deceive the GK, whereas the FREE condition more closely resembled the penalty shot because shots were taken immediately without baulking. The effect of baulking on the speed and accuracy of the water polo shot has not yet been determined; however, it seems likely that optimal throwing technique is compromised as a result of this practice. Furthermore, a successful baulk results in premature movement on the part of the GK, which then reduces the demand for speed and accuracy of the shot, because a successful shot is possible at reduced speed and accuracy if the GK is further from the intended target. Second, throws under the GK condition were performed after the FREE shots; consequently, the fatigue effect may also explain the reductions in speed and accuracy. Given, however, that this population is accustomed to this frequency and number of shots, and that shots were performed at self-selected speed with large recovery periods between sets, this explanation seems unlikely.

During the FREE and GK conditions, players threw at 90.1 and 88.1% of MTS, respectively. These values are similar to those reported for elite and novice male handball players when asked to optimize both speed and accuracy (93 and 92%, respectively) (19,20). These values are, however, higher than those reported for elite and novice male handball players (75–85% and 84%, respectively), as well as male and female cricket players at elite and sub-elite levels (75–80%) when asked to optimize accuracy alone (11,12). In light of the fact that a significant speed-accuracy trade-off exists in throwing, such that accuracy is reduced with increases above approximately 75% of MTS (11,12,19,20), this data suggest that elite female water polo players were attempting to simultaneously optimize speed and accuracy and highlights the importance of both of these parameters to successful shooting performance in water polo. That is, a high degree of throwing speed is of little value if not accompanied by a high degree of accuracy, and vice versa. As a result, the speed-accuracy trade-off is an important consideration in water polo.

Maximal throwing speed remained consistent, whereas accuracy improved across the 3 pre-Olympic testing sessions. This is evidenced by statistically significantly higher hit percentages during session 3 compared with sessions 1 and 2, as well as statistically nonsignificant trends toward improved accuracy across each of the specific error parameters (E, X, Y, ACE, and VE). Consequently, we propose that this improvement in accuracy resulted from a combination of moderate statistically nonsignificant improvements in each of the accuracy parameters. Although not engaged in explicit throwing speed or accuracy training over the course of the testing sessions, participants were engaged in regular tactical and game-based practice sessions, involving penalty shots and shooting from general play. In addition, the participants also experienced a statistically significant reduction in training workload by the time of the third testing session. It is possible that these factors lead to the accuracy improvements; however, this is speculative and requires further investigation.

Of interest to coaches, vertical error was greater than horizontal error across all conditions. The group centroids revealed that these errors occurred predominantly above the target, resulting in the ball either striking the goal frame or missing the goal completely. When throwing to targets at the top of the goals, vertical errors in the downward direction are more advantageous, as throws made above these targets have no chance of resulting in a successful shot, whereas shots below the top targets, while potentially more easily defended, still have a chance of producing a successful outcome. Even in this elite-level population, errors are predominantly made in areas that are of little value to the shooter. We, therefore, identify this as an area of potential improvement in water polo performance. Training programs that reduce overall error, but more specifically, reduce error in directions that result in low shot success should be developed and implemented.

Variable error was greater than ACE across the 3 testing sessions. This study is the first time that these variables have been measured in a group of water polo players; consequently, little is known regarding the causal mechanisms of bias and consistency during water polo shooting; however, these values are similar to those reported during throws made by European handball players (19,20).

This study is the first to describe the reliability of throwing speed and accuracy measures for female water polo players. Maximal throwing speed demonstrated very high test-retest reliability. A strong negative correlation was observed between total error and hit percentage. Overall, total error was a slightly more reliable measure of accuracy than hit percentage; however, when FREE and GK conditions were explored separately, hit percentage was more reliable than total error during FREE, whereas total error was considerably more reliable than hit percentage during GK. Consequently, although, hit percentage can provide a fast, reliable, general measure of accuracy without a GK present, total error should be measured when testing involves the presence of a GK or any time when the nature of shooting error needs to be described.

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Practical Applications

This study provides a benchmark for Olympic-level throwing performances in female water polo players. This information should be used by coaches to compare and motivate junior and sub-elite athletes aspiring to play at elite levels of competition. Water polo training should involve the presence of a GK, whenever possible, to simulate in-game demands and help attenuate the reduction in performance (both speed and accuracy) that results from having a GK present. Whenever possible, accuracy should be described in terms of total error and its directional components. This information can be used to better understand the errors that individual players are making, to allow for athlete-specific training practices to be developed and implemented. Hit percentage is a reliable substitute for total error but only when a GK is not present and when knowledge of the nature of errors incurred is not valuable to the coaching process. Given the highlighted importance of the speed-accuracy trade-off in water polo shooting, strength and conditioning coaches seek to improve the strength and power production capabilities of their athletes, leading not only to increased MTSs but also improved accuracy at submaximal speeds.

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Acknowledgments

The results of this study do not constitute endorsement of the product by the authors of the NSCA. No external funding was received for this study. There are no conflicts of interest to declare.

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Keywords:

overhead; precision; velocity; speed; acuracy

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