|The Shot: What the research has found|
|Friday, 13 June 2008 15:42|
There have been a number of research papers written examining the shot at goal in water polo (e.g. Davis and Blanksby, 1977; Whiting et al., 1985). These have described the movements which generate ball speed in elite throwers, compared high and low skilled players, males and females, fast and slow shooters to find important technical factors that make a good shooter. The major findings are summarized in the highlighted section. For more info, read on ....
Summary of Research Findings
Technique Differences Between Skill Levels and Between Fast and Slow Shooters
During the 10th FINA World Cup, 94 players from eight different national teams were asked to shoot at goal with maximum ball speed using a direct shot and a shot with 2-4 feints or baulks. Ball speed for direct shots averaged 73 kph, with a range of 58 to 88 kph (Darras, 1998). No statistical difference in ball speed was found between teams nor between the direct and feint shots.
In other studies, national team members have been shown to throw with greater ball speeds than club players (Davis and Blanksby, 1977; Natunen, et al., 1995).
In the only study to report elite level female shooters (national and international), speeds of 53 kph were found (Elliot and Armour, 1988).
Ball speeds are lower than in other throwing sports such as baseball pitching (108 to 135 kph with a maximum of 162 kph recorded in a US major league game, Atwater, 1979) and the European handball standing throw (62 - 85 kph, Joris et al. 1985, Hoff and Almasbakk, 1995). The differences are due to the water environment and the larger ball in water polo, which reduce the ability to generate force while maintaining ball control.
Using US college players, Feltner (1994) examined the shooting technique of a 4m penalty shot with the aim to generate maximum ball speed. Using a mathematical technique to calculate the contributions of various movements to generating ball speed, he found that different players used two different techniques: an overhand throw technique (OT) and a sweep technique (SW).
OT is described in many coaching texts and is considered the main shooting technique. SW is also referred to as the sweep, sling or straight-arm technique.
As can be noted in Table 1, while trunk rotation and elbow extension contributed significantly in both techniques, OT used internal rotation of the upper arm, while SW used horizontal adduction to produce ball speed at release (see Figure 1). Both techniques produced similar ball speeds. However, the SW technique required greater muscular effort and produced greater peak varus stresses on the elbow (sideways bending, affecting the inside edge of the elbow which may increase the chance of injury, Feltner and Taylor, 1994).
Interestingly, three of the movements that generated ball speed in the water polo throw are not used to generate ball speed in on land throwing. Internal rotation is considered to be an injury prevention movement, which allows the forearm to continue its path across the body without reaching the limits of elbow range of motion (Feltner and Dapena, 1986). Elbow extension is caused by the centrifugal force created by the trunk action 'slinging' the forearm outward rather than the action of the triceps (Feltner and Dapena, 1986). Horizontal adduction is considered a technique error in on land throwing (Kreighbaum and Barthels, 1983).
Due to the reduced trunk and leg force development in throwing in water, as well as the larger ball size reducing wrist involvement, other movements must generate speed in the water polo throw; hence the greater use of horizontal adduction, internal rotation and elbow extension in the water compared to on land throwing.
These findings have implications for technique as well as movements that should be targeted in strength/flexibility programmes.
Technique Differences Between Skill Levels and Between Faster and Slower Shooters
Hip and shoulder movement during the shot
Ball (1996a) filmed and analysed both above and below water technique for a group of junior and senior international players shooting for maximal speed at a goal approximately 7 metres away and found:
Hip rotation peak velocity occurred before shoulder rotation peak velocity in faster shooters, while hip and shoulder rotation peak velocities occurred at the same time for slower shooters. This meant that the better shooters added another segment in the kinetic chain (which provides greater potential for developing ball speed - see "The shot described" on this site) and made use of the trunk muscles in developing speed. Conversely, the slower shooters used the trunk as one segment only and as such, the trunk muscles were only used to stop rotation in the trunk, rather than actively accelerate the ball.
On land throwing in sports such as baseball and javelin throwing have also identified good hip and shoulder rotation as important in maximal speed throwing (eg. Baseball: Vaughn, 1988; Javelin: Bartlett and Best, 1988).
Coaching Implications: Emphasize good hip rotation to start just before the top of backswing
Height out of the water
This factor, often a coaching point, was found to be unimportant in generating ball speed and was not different between skill levels (club - national - international) nor male and female players (Davis and Blanksby, 1977; Elliott and Armour, 1986; Ball, 1996b). This was contradictory to Lambert and Gaughran (1969) who stated that the vertical level out of the water that is achieved by the shooter is the best indicator of ball speed. Davis and Blanksby (1977) suggested that an optimal rather than a maximal height out of the water influences ball speed.
Authors note: The players tested in these studies were largely of high skill level, where it might be expected that all players could achieve reasonable height out of the water. In lower skill level players, height out of the water may become important, as they cannot clear the water to achieve a free throwing motion. The lack of height out of the water may also be indicator of poor underwater action which will generate less hip rotation and a less stable base from which to throw.
Coaching Implications: Rather than using cues like "get higher out of the water", encourage players to "get out of the water and rotate your hips".
Backswing and forward swing
The length of backswing and forward swing (measured by the distance the ball moves) did not differ between club and national team players (Davis and Blanksby, 1977). Elliot and Armour (1988) also found no difference in the length of forward swing between males and females.
Male shooters make a more horizontal path with the ball during backswing compared to a more vertical path exhibited by females (Elliot and Armour, 1988). They suggest that the horizontal path may conserve the momentum built up in backswing and better transfer it into forward swing, as opposed to a complete stop at the top of backswing, which was evident in the female throwers (females brought the ball straight back, paused at the top of backswing then brought the ball straight forward).
Coaching Implications: Encourage a smooth transition from backswing to forward swing.
Forward movement of the body in forward swing
International players have been found to move their head/trunk forward further (Davis and Blanksby, 1977) and faster (Natunen et al., 1995) in the forward swing than club level players.
However, Ball (1996b) found that forward movement of the centre of gravity was not related to ball speed in elite players. He suggested that it may not discern elite level throwers because they all have reasonably good forward movement or have optimized their particular strengths and weaknesses. Ball (1996b) also suggested that it may have been due to the existence of two techniques in players tested - a rotational style (similar to SW in Feltner, 1994) in which little forward movement occurred and an overhand style (similar to OT in Feltner, 1994) in which it did.
Coaching Implications: At Club level, encourage forward movement during the forward swing but be aware of players who use a rotational (sweep) technique, as forward movement may not be as useful to this technique.
Top of backswing
Davis and Blanksby (1977), compared four Australian national team members and four club level players performing a shot at goal filmed from above water and found that national team members positioned their upper arm more vertically as viewed from side-on (figure 3).
National team players also held the ball further behind their head as viewed front-on (Figure 4).
Coaching Implications: Encourage a top of backswing position that holds the ball high and back behind the head.
As mentioned earlier, Feltner (1994) found that wrist flexion was an active contributor to developing ball speed in college level water polo players. Elliot and Armour (1988) found that males but not females used wrist flexion and extension during the throwing motion. Males would begin with a flexed wrist at the top of backswing, extend it as it passed by the head then flex it again as the ball came off the palm near ball release (but remained in contact with the fingers).
The use of the wrist effectively adds a segment to the kinetic chain and increases the potential to develop ball speed. Ball control is an obvious problem with the use of the wrist, as found in the Elliot and Armour (1988) study where females (with smaller hands) could not control the ball as well as males and did not show wrist flexion at release.
Wrist flexion is significant in other throwing sports. For example, Peterson (1973) reports that wrist flexion contributed 23.9% of ball speed in baseball pitching. However, Cooper and Glassow (1968) report that wrist flexion contributed as little as 3% to ball speed when a larger ball was thrown, as ball control becomes a factor. While this is the case in water polo, the use of the wrist hold great potential for increasing ball speed, as evident in other throwing tasks. Improved ball control, allowing for wrist flexion during the throw, will increase the potential for developing ball speed.
Coaching Implications: * Encourage wrist flexion late in the swing, provided the player has adequate ball control. * Try drills that improve ball control or improve the timing of wrist flexion (after the ball has left the palm but is still in contact with the fingers) so that players can add more wrist flexion to the shot.
Although a strong underwater action is recommended in coaching texts and in past research, there has been only qualitative assessment of the underwater technique during the shot. See "The Shot: Underwater action" on this site for more detail on this technique.
Summary of Coaching Implications