The biomechanical structure of a stroke in table tennis

A stroke in table tennis represents a kinematic chain in which the initial momentums are given by the leg muscles, and then successively the body, shoulder, upper arm, forearm and wrist, respectively. This means that the parts of the body with a greater mass followed one after the other by body parts with a smaller mass, ending with the wrist in such a kinematic chain (Hudetz, 2000).

The biomechanics of the service in table tennis establishes that this action is produced by a combination of forces: internal, understood like the muscular force able to produce a change in the different involved biocinemáticas chains in the action due to the organic composition of muscles, the tension of fascias, ligaments and sinews. Therefore, not only does the table tennis player ensure that the effectors coincide with the target in time and space, but also that

the bat arrives at the interception with suitable kinematics for the ball to be returned to the opponent’s side of the table (Garcia, 2003; Sheppard & Li, 2007).

In a short review of the literature, Cortés, Fuente, Pagan, and Revelles (2003) examined whether there were any differences in maximum meaningful force between the dominant and the non-dominant members of the superior players who practiced table tennis at a high level.

They aimed to analyze whether this was a crucial factor for the performance of table tennis players. They found considerable differences in maximum manual force in men, who were bigger than women. Moreover, they reported that the manual high force was greater for the dominant player against the non-dominant one, as well as for left-handed or right-handed players. Finally, they demonstrated that left-handed players have a record of slightly higher force than right-handed ones.

Success in table tennis is greatly affected by the technique a player uses, and biomechanics plays an integral role in stroke production. All strokes have a fundamental mechanical structure, and sports injuries primarily have a mechanical cause. Player development based on scientific evidence allows an individualized approach to be structured, with due consideration to the key mechanical features of each skill, while also fostering flair and permitting the physical characteristics of a player to be considered. An understanding of biomechanics from a sports medicine perspective is also important if player development is to occur with minimal risk of injury (Elliott, 2006).

Considerable biomechanical research has examined the effects of various data smoothing procedures on errors in subsequent calculations of higher-order kinematic variables (Knudson

& Bahamonde, 2001).

Summing up kinetic measures (such as the net joint moment or net joint moment power) of the individual lower extremity joints has been used in biomechanical research to ascertain a single measure of lower extremity function during human movement (Flanagan & Salem, 2005).

The most appropriate smoothing depends on the specific kinematic variable. The information is required on the best extrapolation conditions to accurately model the angular velocity in sport biomechanical skills involving impacts (Knudson & Bahamonde, 2001).

Many biomechanical theories have tested the skill specific, fundamental movement pattern specific, and generic theories, principles or concepts of biomechanics (Knudson, 2007).

Sport biomechanics has generally concentrated analyses of performance on sports in which the movement technique is critical. Such sports involve predominantly closed skills. These are classified as acrobatic, including gymnastics, trampoline gymnastics, diving and freestyle skiing, athletic, including jumping and throwing, and cyclic, including running, swimming, skating and wheelchair racing (Hughes & Bartlett, 2002).

Sports biomechanics began with attempts to apply physics in coaching sports. With a few exceptions, most sports biomechanics books are physics books using sports examples for illustrations. However, there are some problems in the science of sport biomechanics.

Although there has been much research on sports biomechanics, and there are more journals as outlets for these reports, further research cannot keep up with all the technical issues and the changes in equipment in sports, and it is difficult for most people to learn the laws of Newtonian mechanics (Knudson, 2007).

Iino et al. (2008), for instance, made an interesting experiment on eleven advanced male table tennis players. They used two high-speed cameras (IPL and IP, Photosonics, Inc.) at a nominal rate of 100 frames per second from the front and lateral sides of the participants.

Each camera was mounted on a tripod placed on the floor, and the spherical was in the shoulder, elbow and wrist. Five markers were attached on each racket (i.e. one marker was attached to the racket tip and the other attached to the lateral side of the racket). They used a ball machine, and the machine was located at the end of the backhand side of the other court.

During their experiment, some of the markers were obscured behind the body or the racket of the participant in some frames of the film images. They reported that to reduce the possibility of obscured markers, each camera tripod was placed on a 1.4 m high platform while filming the collegiate players. They found that the mean speeds of the topspin and backspin balls just before impact were 20.2 m/s. In addition, there was no significant difference between the two types of backhand in the magnitudes of the joint and segment angular velocity of the racket arm at impact. There was no significant difference between the two types of backhand in racket tip forward velocity at impact. There was no significant difference between the two types of backhand in any contribution to forward velocity. The contribution of elbow extension was significantly smaller against backspin than against topspin. The negative contribution of elbow extension was significantly smaller against backspin than against topspin. The contribution of the wrist to the upward velocity was greater against backspin

than against topspin. The contribution of the upper arm external rotation to the upward velocity was greater against backspin than against topspin.

In another example, Knudson & Bahamond (2001) examined if smoothing through impact was responsible for the apparent decrease in racket speed before impact in tennis. They aimed to assess the accuracy of two recent techniques of impact point estimation and extrapolation.

They found that all smoothing methods more closely approximated the true wrist angle data in the five point linear extrapolation and polynomial extrapolation conditions. They reported that racket speed decreased before impact in tennis smoothing data through impact created systematic errors in the position.

Accurate kinematics data near impact are important in documenting the coordination of movement. That made a lot of previous studies focus on the pattern of the velocity of segments. Motor control studies have focused on an apparent decrease in speed (i.e. negative acceleration) before impact as a potential accuracy enhancing strategy (Knudson &

Bahamonde, 2001).

Expert table tennis players have been shown to execute their drives with remarkably consistent movement times. This is the time between the first persistent forward motion of the racket and the moment of ball contact (Bootsma & Van Wieringen, 1990).

Moreover, Laurent, Montagne, and Savelsbergh (1994) aimed to identify the control mechanisms involved in a goal directed task by manipulating the temporal constraints. The table tennis balls projected by a ball projection machine had fewer than five temporal conditions (ball speed ranged from 5.7 to 9 m/s, giving rise to flight times of 550-350 ms).

They used three-dimensional kinematic analysis. They found decreases in movement time and increases in the straightness of the trajectory of the wrist.

Furthermore, teaching motor skills implicitly may not be an easy task. In learning the skill of basketball shooting, for example, even if the learner is a total novice and no instruction is given, explicit learning will be inevitable. During practice, the learner will compare his or her own movements trial by trial to try to figure out the most effective shooting techniques (Liao

& Masters, 2001).

Therefore, in evaluating movements the coach would notice several strengths and weaknesses in the application of biomechanical principles to table tennis skills. The coach may mentally note that the coordination and timing between back swing and forward swing was good, and

the player hit the ball. Thinking in terms of biomechanical principles, he or she can conclude that the player also made a good compromise between weight shift and balance for the beginning player (Knudson, 2007).