Introduction
Throwing performance with differently weighted medicine balls is often used for monitoring training effects (4,14,25) and as a selection tool for young athletes (20). Some of the most commonly used throwing techniques are the seated chest throw (21) and the standing overhead throw with medicine balls (23,24). Additionally, unilateral medicine ball throws are also sometimes used for evaluating upper body strength (12,16). However, because of safety concerns, this is normally limited to throws with lightweight balls (17).
In terms of evaluation criteria, distance (22) and throwing velocity are considered valid measurements of individual throwing performance (23,24). Nevertheless, in evaluating throwing velocity, some authors have used different methods such as photocell gates (11,26) and high speed video (8,10). Nevertheless, these 2 testing methods require sophisticated and expensive equipment together with skilled personnel.
More recently, several researchers have reported throwing velocity measured with a Doppler radar gun (12,16,24). The equipment is reliable, easy to deploy, and cost effective. It is already widely used in evaluating several fast discrete movements such as the soccer kick (17), volleyball spike (9), and tennis stroke (7). On this, Markovic et al. (15) showed that the Doppler radar gun may be used in obtaining highly reliable (ICC between 0.94 and 0.96) estimates of maximal kicking velocity in soccer. In addition, Harasin et al. (12) also reported high reliability (ICC between 0.97 and 0.98) in 3 commonly used throwing tests with the radar gun. The authors evaluated 77 physical education students in a seated 1-arm handball throw (0.45 kg), a seated 1-arm medicine ball throw (1 kg), and a seated medicine ball chest throw (3 kg). However, to the best of our knowledge, no prior study has simultaneously evaluated the reliability of both standing and seated throwing based on ball release velocity. Moreover, load variations during throwing have not so far been evaluated, a factor that might affect reliability.
Therefore, the aim of this study was to determine the reliability of release velocity during a seated chest throw and a standing overhead throw with 3 differently weighted medicine balls. It was hypothesized that reliability increases in line with increases in weight as previously suggested (12). It was furthermore assumed that reliability would be greater in seated throws than in standing throws because of the limited use of body segments. Although in the seated chest throw mostly the arms and shoulders are used, in the standing overhead throw, both the upper body and hips would be used.
Methods
Experimental Approach to the Problem
To test the reliability of the ball-throwing velocity in a seated chest throw and a standing overhead position involving 3 differently weighted medicine balls, a within-subjects repeated-measures design was used. Reliability was tested as follows: systematic bias, random error, and retest correlation (13,27).
Subjects
Seventy-nine (55 men and 23 women) college sports science students (age 21.7 ± 2.1 years, mass 71.5 ± 11 kg, height 1.75 ± 0.09 m) participated in this study. The participants were fully informed beforehand as to the relevant protocol. Informed consent was obtained before all testing, in accordance with the approval of the regional committee for medical and healthcare research ethics and following the current ethical guidelines in sports and exercise research.
Procedures
Before the test, the participants were familiarized with the process of throwing using the variably weighted balls and the 2 different throwing techniques. They underwent 6 weeks of twice-weekly training in overhead throwing to control for potential learning effects. Seated chest throw familiarization was treated differently in that it was practiced on only 1 occasion 6 weeks before testing. In both cases, this was done to avoid a learning effect. Throwing was performed with a 1-kg medicine ball (circumference 0.72 m), a 3-kg medicine ball (circumference 0.78 m) and a 5-kg medicine ball (circumference 0.85 m).
A 10-minute warm-up immediately preceded testing and consisted of exercises to warm up the shoulders plus submaximal throwing efforts with the different weighted balls (3–5 throws with each weighted ball). Five minutes thereafter, testing commenced with the standing throw mimicking a standard soccer throw-in. The participants stood with both feet parallel to each other during the entire process. They all started by holding the ball to the front with both hands and were then instructed to throw the medicine ball as far and fast as possible with both hands over the head and hyperextending the back and shoulders (soccer throw-in movement). Both feet were kept on the ground at all times during and after the throw, and no preliminary steps were allowed. Torso and hip rotation was also not allowed (23,24). Failure to keep both feet on the ground during the throw resulted in disqualification and a new attempt was performed after 1 minute of rest. In the seated position, the participants sat on the ground with their legs in front of them with both hands on the chest. They were then instructed to throw the medicine ball with maximal effort from the chest in a straight line ahead. The research leader (expert in analyzing throwing movements) controlled the correct throwing techniques during the study. Three attempts were made with each ball and throwing style with a 1-minute rest between each attempt. The sequence of ball weight and throwing style was randomized for each participant to ensure that fatigue or learning effects did not alter performance. The maximal ball-throwing release velocity with the different balls was determined using a Doppler radar gun (Sports Radar 3300, Sports Electronics Inc.), with ±0.028-m·s−1 accuracy within a field of 10° from the gun. The radar gun was located 1 m behind the participant at ball height during the throw.
Statistical Analyses
In testing reliability, the same procedures were used as Harasin et al. (12) who also studied reliability in other throwing tests. Reliability was tested in all 3 different ways: systematic bias, random error, and retest correlation (13,27). The systematic bias between the 3 consecutive attempts was calculated by a 1-way analysis of variance (ANOVA) for repeated measures on each medicine ball weight and type of throw. Where the sphericity assumption was violated, the Greenhouse-Geisser adjustments of the p values were reported. The post hoc comparison of Tukey was used for comparing eventual differences between the 3 throws. Random error (i.e., within-individual variability) was estimated by Bland and Altman's 95% limits of agreement (3). The absolute limits of agreement (LOAs) were calculated by the root of the mean squares error of the repeated measure ANOVA (RMSE) for each throwing text. The RMSE was multiplied by 2.77 to obtain the 95% random error component (2).
The retest correlation was expressed as an intraclass correlation coefficient (ICC) and was calculated from the ANOVA for repeated measures. An ICC >0.90 is considered to be high and shows high reliability. The level of significance was set at p ≤ 0.05, and all data are expressed as mean ± SD. Statistical analyses were performed in SPSS version 18.0 (SPSS, Inc., Chicago, IL, USA).
To test if the variability changes within participants when throwing with the 2 different techniques and different weights, a repeated 2 (type of throw: seated, standing) × 3 (ball weight: 1, 3 g, 5 kg) ANOVA design on the SD of the 3 attempts with each ball weight and technique was used. Post hoc analyses with Bonferroni correction were conducted to determine significant differences. Effect size was evaluated with
;)
(Eta partial squared) where 0.01 < η2 < 0.06 constitutes a small effect, a medium effect when 0.06 < η2 < 0.14 and a large effect when η2 > 0.14 (6).
Results
Figure 1 shows that velocity in the standing overhead throw obtained over the 3 consecutive attempts increased significantly (Table 1) from the first to the last with all 3 medicine ball weights. However, no significant difference was found in the 3 consecutive seated attempts across the different medicine ball weights (Figure 1, Table 1).
Figure 1: Maximal throwing velocity of (A) the standing overhead throw and (B) the seated chest throw with the 1-, 3-, and 5-kg medicine ball for the first, second, and third attempts averaged over all the participants. *Significant difference between these 2 attempts (p < 0.05).
Table 1: Descriptive statistics (mean and SD) on the components of reliability of the 2 throwing techniques with the 3 different ball weights.*
The random error displayed by the limits of agreement ranged from 0.23 to 0.43 m·s−1 as viewed in Table 1. Retest correlation as expressed by the ICC was very high for all throwing tests, ranging from 0.88 to 0.96 (Table 1).
Significant differences in variability changes within participants were found for both the throwing weights (F = 7.5; p = 0.001; η2 = 0.174; stat. power = 0.934) and between the 2 techniques deployed (F = 89.8; p < 0.0001; η2 = 0.55; stat. power = 1.0) with no significant interaction effect (F = 1.18; p = 0.31). Post hoc comparison with Bonferroni correction showed that the SDs in the standing throws were larger than in the seated throws and that the SD when throwing with the 5-kg ball was significantly less than with the other 2 ball weights (Figure 2). Furthermore, the SD in seated throws with the 1-kg medicine ball was significantly higher than in the other 2 balls (Figure 2).
Figure 2: SD over the 3 attempts within each participant averaged per ball weight and throwing technique. *Significant difference between standing and seated throws (p < 0.05). †Significant difference in SD between these 2 parameters (p < 0.05). ‡Significant difference in SD in throwing between these 2 ball weights (p < 0.05).
Discussion
In this study, reliability was tested in 3 different ways: systematic bias, random error, and retest correlation in standing overhead and seated chest throws with 3 differently weighted medicine balls. A systematic bias was observed for overhead throwing but not for seated chest throwing (Figure 1). Moreover, the variability of maximal throwing velocity decreased with increasing ball weights and was much higher in standing throws compared with the seated chest throws.
A systematic bias was found when performing overhead standing throws (p < 0.001, Table 1), but not in the seated chest throws (p > 0.06, Table 1). This was very surprising, because the overhead throws were practiced twice a week over a 6-week period performing only standing overhead throws, whereas the seated chest throws were practiced on only 1 occasion 6 weeks before testing. Although the participants were not experienced throwers, this training period was thought sufficient to avoid a learning effect for this specific test. An explanation for the increased velocity over the sequential attempts in the standing overhead throw could be that it was the result of fine tuning. Because the participants trained relatively intensively for 6 weeks, it was possible they were able to adjust their throwing pattern and increase their throwing velocity from attempt to attempt (they received feedback on the throwing velocity after each attempt). The sequence of throwing was randomized for each participant to avoid a systematic fatigue and learning effect. However, this might well result in a postactivation potentiation in the throws in which they trained (1,19). In the seated chest throws, they lacked experience and were therefore still trying to work out how to throw faster. For some participants, this could result in an increase of velocity in subsequent attempts, whereas in others, it could result in decreased throwing performance. Therefore, no systematic bias was observed. Furthermore, the seated throwing position allowed constrained use of body segments compared with the standing throws. This may have produced more stability and less variability in their attempts (18). This would agree with the finding of Harasin et al. (12) on seated chest throws with a 3-kg medicine ball.
Within-participant variation is analyzed by the random error in influencing the precision of measurement in a study. It is therefore considered the most important type of reliability for researchers and practitioners (5,13). The LOA varied from 0.23 to 0.48 m·s−1 for the seated chest throw with 5 kg and the standing overhead throw with 1 kg, respectively. When the SD of the 3 attempts per participant was averaged for each ball weight with each throwing technique, differences in variability within participants were found for both the throwing weights and for the 2 techniques deployed. This indicates that ball weight and technique influence the variability within a given individual. It was found that the variability decreases with increases in throwing weight, a result also hypothesized in this study and in line with the findings reported by Harasin et al. (12). Reasoning for this decreased variation within a given participant with increasing weight can be explained by the fact that with increasing ball weight the throwing velocity decreases and therefore the variation possible in throwing velocity also tends to narrow (8). Additionally, the differences in variability between the 2 throwing techniques can be explained by the kinematics and musculature involved. Indeed, in the seated chest throw, the participant can only push the ball from the chest while flexing the shoulder, extending the elbow and flexing the wrist joints, while in the standing overhead throw, the ball starts from behind the head, thereby implying a more prolonged application of force to the ball. In contrast, in the standing overhead throw, the shoulder joint is extended and the trunk flexed forward while throwing. This longer throwing trajectory, together with the greater number of joint movements involved, may well influence throwing performance (18). In this way, the variability of throwing performance could show an increase, as found in this study (Figure 2).
The third important component of reliability is the relative reliability (13), which was measured by the intraclass correlation coefficients (ICCs). Here, the ICC ranged from 0.88 (5-kg standing throw) to 0.97 (1-kg seated throw), which shows high relative reliability. The ICCs observed in this study are in line with those found in previous studies. In the seated chest throw with a 3-kg medicine ball, Harasin et al. (12) reported an ICC of 0.97. Similar reliability was shown for the standing overhead throw with a 5-kg medicine ball (ICC: 0.93; van den Tillaar and Marques [23]), 3 kg (ICC: 0.86; van den Tillaar and Marques [24]), and also with a 1-kg medicine ball (ICC: 0.93; van den Tillaar and Marques [24]).
Further studies are required to evaluate whether the findings are replicable where the same tests are applied to highly skilled throwing participants or participants of different ages.
In summary, when evaluating the throwing velocity in standing overhead and seated chest throws with different ball weights, a Doppler radar gun can be effective in guaranteeing high reliability. However, reliability can be affected by such factors as throwing weight and technique, which can be of relevance when conducting studies with these parameters.
Practical Applications
With the widespread support of strength and power training in the adult, the practitioner must have reliable and valid field test measures to assess baseline status and to monitor response to training. A Doppler radar gun can be used in evaluation throwing velocity in standing overhead and seated chest throws with high reliability. However, throwing weight and type of throwing technique can affect reliability, that is, with increasing ball weight up to 5 kg, and using the seated chest throws instead of the standing overhead throws (limiting involvement of several joint movements) appears to enhance reliability. These are especially important considerations for coaches and trainers who want to test training effects after a training period or for researchers when conducting training studies.
Acknowledgments
The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association. This study was conducted without any funding from companies or manufacturers or outside organizations.
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