PHYSICAL TRAINING IN SPORTS
Physical fitness is a very important factor affecting performance in sports. As in the preparatory phase of periodization plan for any training programme, the physical fitness is always the first to be developed before focusing into other training factors such as technical training, tactical training, and psychological training. Physical fitness contributes to sports performance. It serves as a foundation that leads to high performance level in sports (Bompa & Haff, 2009).

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Many researchers have studied various types of physical fitness training, such as balance training (Myer, 2005; Myer et al., 2006), agility training (Miller et al., 2001; Young et al., 2001; Holmberg, 2009), sprinting training (Markovic et al., 2007), resistance training (Candow & Burke, 2007; Sturgess & Newton, 2008; Hamberg-van Reenen et al., 2009), circuit training (Chtara et al., 2008; Duncan et al., 2009), interval training, and plyometric training (Gehri et al., 1998; Swanik, 2002; Spurrs et al., 2003; Turner et al., 2003; Myer, 2005; Miller et al., 2006; Myer et al., 2006; Saunders et al., 2006; Salonikidis & Zafeiridis, 2008; Vescovi et al., 2008; de Villarreal et al., 2008; Meylan & Malatesta, 2009; Thomas et al., 2009; Ebben et al., 2010; King & Cipriani, 2010; Rubley et al., 2011) and many studies found that physical training served the purpose of improving various physical attributes, such as flexibility, functional performance, muscular control, muscular power, distance running performance, running economy, strength performance, explosive power, vertical jump, initial acceleration, speed, and agility (Gehri et al., 1998; Swanik, 2002; Spurrs et al., 2003; Turner et al., 2003; Kotzamanidis, 2006; Miller et al., 2006; Saunders et al., 2006; Markovic et al., 2007; Chtara et al., 2008; de Villarreal et al., 2008; Jullien et al., 2008; Salonikidis & Zafeiridis, 2008; Vescovi et al., 2008; Meylan & Malatesta, 2009; Thomas et al., 2009; Walklate et al., 2009; Sáez-Sáez de Villarreal et al., 2010).
PHYSICAL TRAINING IN BADMINTON
Badminton is a highly competitive dynamic sport. At elite level, it is suggested that badminton is characterized by repetitive efforts of alactic nature and great intensity which are continuously performed throughout the match (Cabello Manrique & González-Badillo, 2003; Lees, 2003; Faude et al., 2007; Sturgess & Newton, 2008). Badminton players are required to be able to move in multiple directions while smashing and receiving a shuttlecock at high speed. The speed of a shuttlecock can be up to 421kph (Guinness World Record, 2009).
Badminton players are often required to perform speed, agility, flexibility, endurance, and strength capabilities at their limit. It is proposed by Badminton Association of England (2002) that the off-court type of fitness training for badminton can include strength training, aerobic training, speed and agility training, flexibility training, core stability training, and circuit training.
As an explosive sport, badminton performance can be enhanced from resistance training. Effective resistance training programme requires a systematic process of analysis, implementation and evaluation to ensure maximum adaptation and improvement. The prescription of resistance training methods can enhance badminton specific performance in jump smashes, lunges, and quick change of direction (Sturgess & Newton, 2008).
AGILITY IN SPORTS
Agility is an essential element for many sports. It is an ability that involves a rapid whole body movement with changes of direction or velocity in response to a stimulus. In many competitive sports such as badminton, the players do not perform at their own pace and move, but are performing in response to the shuttlecock, the opponent, or the partners. As such, agility in badminton is not completely an independent factor (Young et al., 2002; Sheppard & Young, 2006; Young & Farrow, 2006; Jullien et al., 2008).
Little and William (2005) proposed that agility is a specific physical attribute that is fundamentally important to sports performance for three reasons. First, developing agility will provide a strong foundation for muscular control and motor skill function, thereby establishing overall performance in badminton. Second, good agility enable players to move fast in balanced and stabled manner, and this proper movement mechanics and this may reduce injury risk. Finally, as an athlete matures, a heightened ability to quickly change directions will enhance overall performance in both proactive offensive and reactive defensive circumstances.
According to Young and Farrow (2006) and Vescovi (2008), agility is important as many sports such as badminton performed on a court require high-speed total body movements. Many of these movements are in response to the motion of the shuttlecock, opponents, or partner. As such, quick movements are very important.
Deterministic Model Of Agility Performance
The multifactorial nature of agility has been represented by a deterministic model in Figure 2.1 which indicating the various factors contributing to performance in sports included badminton (Young et al., 2002). The model (Figure 2.1) indicated the agility can be affected by perceptual and decision making factor, and change of direction speed.
Perceptual and decision making is one of the main factors affecting agility. The factors affecting perceptual and decision making included visual scanning, anticipating, pattern recognition, and knowledge of the condition.
Leg muscle qualities
Change of directional speed
Young and Farrow (2006) noted that agility is affected by the change of directional speed. Change of directional speed is influenced by the techniques, straight sprinting speed, and leg muscle quality.
Techniques to change direction and change velocity quickly are expected to be influenced by the position of the body while running. A forward lean is required to accelerate, a backward lean to decelerate and stop, and a sideward lean to produce a lateral change of direction. These body positions are necessary in order to produce forces to the ground to evoke reaction forces in the desired direction. The technique of body lean enables badminton player to make quick adjustments of strides to accelerate and decelerate, to the running posture to execute a quick change of direction. Such quick adjustments of posture and positioning of limbs is clearly a skill that requires training. This can be developed by plyometric training (Meylan & Malatesta, 2009).
Leg muscles quality is exclusively responsible for change of directional movements. The available research provides little support that leg muscle strength, power, and reactive strength are major contributors to agility performance. However, a rationale was made to suggest that plyometric training program involving jumping exercises that contain single leg lateral takeoffs, such as bounding in a zigzag pattern could potentially be beneficial to change of directional speed development (Robinson & Owens, 2004; Miller et al., 2006; Sheppard & Young, 2006; Young & Farrow, 2006; Markovic et al., 2007; Thomas et al., 2009). Good quality of leg muscle in badminton helps to reduce time taken from ready position to move to receive a shot.
AGILITY CONTRIBUTION IN BADMINTON
Motion analysis of a typical badminton match reveals that there are many changes in direction and it requires the athlete to be very agile in all directions (Cabello Manrique & González-Badillo, 2003; Sturgess & Newton, 2008). Notational analysis of European players during international tournaments indicated that badminton can be characterized by repetitive, short-duration, high-intensity efforts with high-frequency movement (Cabello Manrique & González-Badillo, 2003).
Badminton is the fastest sport among the racket games with the speed of the shuttlecocks capable of travelling up to 421kph. This means in the court area of approximately 34m2 for badminton singles, the shuttlecock will take not more than 0.15 second to pass through the entire badminton court which is 13.4m in length (Olympics ABC, 2007). As a sport with such a high speed, agility plays a very important role to contribute to the performance.
In an elite badminton match, the competition can be played up to more than 60 minutes, and the total running distance can be covered up to 6km. But the energy spent for both players were not the same. When a player is more agile and faster than opponent, he can get into favourable position to play the shot to move opponent around in the badminton court which will lead to greater radius of movement for the opponent. In another word, throughout the match, the player who have better agility are having advantage and spending less effort and energy compare to the less agile opponent.
Olympic ABC (2007) also proposed that a player need approximately 0.32 to 0.36 second to move from a ready position towards the shuttle and approximately 0.486 seconds to react to the coming shot. This lead to an idea that a badminton player needs about 0.8 second to react to a shot and move to receive the shot. In this condition, agility is a critical factor affecting the performance. Time taken to react to the coming shot is affecting by the perceptual and decision making factor, while the time taken to move from a ready position towards the shuttle is affecting by the agility, which have the direct relationship with the change of direction speed. Good agility and fast action to move from ready position enable a badminton player to return the shot in a favourable position and have advantage over opponent.
PLYOMETRIC TRAINING IN IMPROVING AGILITY
Plyometrics are training techniques used by athletes in all types of sports to increase strength and explosiveness (Chu, 1998). Plyometric training programme involving jumping exercises that could potentially be beneficial to agility development (Robinson & Owens, 2004; Miller et al., 2006; Young & Farrow, 2006; Thomas et al., 2009).
Plyometric drills usually involve stopping, starting, and changing directions of movement in an explosive manner. These movements are components that can contribute to developing agility (Young et al., 2001; Miller et al., 2001). Previous studies found that plyometric training, when used in a periodized manner, can contribute to agility gains (Miller et al., 2006; Thomas et al., 2009).
Agility is an explosive movement which can be referred to running speed and changes of direction ability. Fast running speed and quick change of direction contribute to good agility. Explosiveness is affecting the running speed and change of direction ability. Thus, improvement in explosiveness leads to agility development. Plyometrics have been proven to be an effective method to improve on explosiveness (Markovic et al., 2007; Chtara et al., 2008).
By enhancing balance and control of body positions during movement, agility theoretically should improve (Miller et al., 2006; Young & Farrow, 2006). Plyometric activities have been used in sports such as football, tennis, soccer or other sports event (Yap & Brown, 2000; Robinson & Owens, 2004). These sports are intermediate sports which require rapid whole body movement with changes of direction or velocity in response to a stimulus, which is similar to badminton.
CONCLUSION
Physical fitness is a very critical factor affecting sports performance. It contributes to sports as the foundation that leads to high performance level in sports. Plyometric is one of the physical training which leads to the gain of various physical attributes which included speed, power, and agility (Miller et al., 2006).
In badminton, a player requires high-speed total body movements. Many of these movements are in response to the motion of the shuttlecock, opponents, or partner. Agility permits badminton player to start quickly and efficiently, move in the correct direction, and to change direction or stop quickly to make a play in fast, smooth, efficient, and repeatable manner, in response to a stimulus.
A competitive badminton match can be played up to more than 60 minutes, agility allow a player to be in the favourable position quickly to play the shot to move opponent around in the badminton court which will lead to greater radius of movement for the opponent. In another word, agility leads to the advantage of lesser effort and energy spent than the less agile player (Olympic ABC, 2007).
Young and Farrow (2006) noted that agility is affected by change of directional speed. Quality of leg muscles is exclusively responsible for change of directional speed. Good quality of leg muscle and good agility in badminton helps to reduce time taken from ready position to move to receive a shot. This enables a badminton player to return the shot in a favourable position and have advantage over the opponent.
Agility refers to running speed and changes of direction in an explosive manner. Fast running speed and quick change of direction is the key to good agility, which is affected by explosiveness. Thus, improvement in explosiveness should lead to agility development. Plyometrics has been proven to be effective and efficient in developing explosiveness (Robinson & Owens, 2004; Miller et al., 2006; Young & Farrow, 2006; Markovic et al., 2007; Chtara et al., 2008; Thomas et al., 2009).
Plyometric drills involve starting, stopping, and change of movement directions explosively. These movements contribute to agility development (Young et al., 2001; Miller et al., 2001). Previous studies showed that plyometric training, when used in a periodized manner, can contribute to agility gains (Miller et al., 2006; Thomas et al., 2009). In addition, plyometric training which enhances balance and body control during movement promotes improvement in agility (Miller et al., 2006; Young & Farrow, 2006).