Returning a tennis serve is one of the most important actions in tennis. Even on the slowest court surface (clay courts), serves and returns are the strokes that influence match results the most in modern tennis games (Gillet et al., 2009). Tennis serves may reach a velocity higher than 200 kph and give a player on a short time to react. However, tennis players also use slower spin serves or second serves with decreased velocity (120 kph). Serve velocity decreases at the moment when a player makes a contact with the ball by 60-70% compared to its initial velocity (Coe, 2000). That means that the time of ball delivery is somewhere between 0.5-1.2 s, depending on serve quality (first and second serve), initial velocity and court surface (Dunlop, 2000). Kleinoder (2001) indicates that average ball delivery time of serves on a clay court is 913 ms for the first serve and 1158 ms for the second serve; however, ball delivery time on a carpet floor (faster surface) is 720 ms for the first serve and 868 ms for the second serve.
The task for a tennis player who is trying to hit the incoming ball from an opponent includes: anticipation and timing, prediction of a ball flight trajectory in space, and the moment of racquet contact (Schmidt, 1991). Crucial factors for a successful tennis return are timing and movement preparation, optimization of the initial position and reacting on velocity and direction of the moving ball during the serve (Vaverka et al., 2003). One of the stages of constructing information coupling is to attract attention to key information sources (Jacobs and Michaels, 2002). Removal of critical information sources at specific developmental stages could impede learning, resulting in unintended changes to coordination of actions, and therefore, while practice task constrains might contain some specific variables, which are available to support learner's actions during practice tasks (e.g. batting against a bowling machine --which is often used in cricket), learners should also be provided with opportunities to pick up specific variables available to support performance in competitive context (Pinder et al., 2009).
Shim et al. (2005a) argue that it is possible to anticipate the type of stroke, but not the direction of the outgoing ball. Other researches (Abernethy and Zawi, 2007; Shim et al., 2006) compared groups of novice players and expert players in a given sport. They show the different cues focusing between the groups and demonstrate higher fruitfulness of anticipation among experts. Singer et al. (1996) says that expert tennis players have a shorter reaction time and a higher accuracy of ball outcome anticipation compared to novice players. Goulet et al. (1989) say that expert tennis players focus their vision more on the opponents' racquet-arm area whereas novice players focus on the ball. Shim et al. (2006) say that a relative racquet and forearm motion provides important information for perception of differences in coordination patterns among different stroke types. This information is not available while using the ball machine. Pinder et al. (2009) suggested that the use of a ball machine changes not only available informational variables until ball release, but also the nature of delivery after ball release.
In other tennis research, Day (1980) showed that skilled tennis players were able to make predictions based on pre-contact cues. Hence most in-situ research was concerned with visual anticipation of ball direction. Williams (1999) says that a player can rely on pre-contact cues more reliably compared to on-line visual information from early parts of a ball flight. Despite the apparent importance of anticipatory cues from server's action, players regularly practice using ball machines (in which anticipatory cues are largely absent). However, information about a ball trajectory is very important to tennis players--it is also called perceptive anticipation (Crespo and Miley, 2002; Poulton, 1957). Renshaw et al. (2007) showed differences in movement initiation of backswing in cricket. Batters who used a bowling machine began the backswing 0.02 s after the ball release. However, the time against a real bowler increased to 0.10 s after the ball release. Similar differences were found in the initiation of downswing--downswing was initiated
0.32 s after the ball release from the bowling machine and 0,41 s after the ball release from the bowler. Pinder et al. (2011) proposed methods of how to optimize developmental programmes in fast ball games and situations, in which a ball machine can be used. It is not clear, how important prior vision of server's action actually is for timing of receiver's movements.
The aim of this study is to examine whether different constraints of returning against a ball machine compared to a real server in tennis affect timing of the return stroke. We hypothesize that movement initiation will be shorter in a group of players using a ball machine. Backswing duration is expected to be longer in a group using a ball machine, but their forward swing is expected to be shorter.