Biomechanical Principles Applied to Badminton Power Strokes

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BIOMECHANICAL PRINCIPLES APPLIED TO BADMINTON POWER STROKES
David B. Waddell and Barbara A. Gowitzke1
Bryson Sport Consultants, Ancaster, Ontario, Canada
1McMaster University, Hamilton, Ontario, Canada
The purpose of the present paper is to review biomechanical research carried out over
the last thirty years on the execution of badminton power strokes, and to share with the
coach important implications of that research. Emphasis is on the forehand and
backhand clear and smash. Results emphasize the importance of the rotational
movements at the shoulder and radio-ulnar joints. Appropriate coaching cues are devised
to assist coaches and players in assessing and improving performance.

KEY WORDS: badminton, biomechanics, power strokes, joint actions, coaching cues

INTRODUCTION: The purpose of the present paper is to review biomechanical research
carried out over the last thirty years on the execution of badminton power strokes, and to
share with the coach important implications of that research.
Thirty years ago, very little research had been done on the game of badminton generally and
none biomechanically. Only hypothetical evidence was available regarding the ‘fast’ strokes
of the game, commonly known as power strokes, i.e., clear and smash. Players and
coaches alike passed along their perceptions of how the power strokes were played, but
none had the benefit of high-speed cameras or other scientific instruments to reveal details
of the performances. In the early 1960’s, Waddell hypothesized that power emanated from
pronation and supination. He based his theories on analysis of his own power strokes as
well as many static photographs of players performing power strokes, which clearly showed
that “wrist snap” was not involved. Poole (1969) wrote, “we . . . rarely ‘snap’ the wrist”, and
“all badminton strokes are made with forearm rotation rather than wrist snap.” Subsequently,
when Poole gathered evidence of this for his dissertation on the upper extremity movements
of world class players (1970), he had to acknowledge that the technology available to him at
that time, cinematographic cameras operating at speeds up to 64 frames per second (fps),
caused him to write a less than definitive qualitative analysis of the clear and the smash.
Other studies concerned with analyses of strokes included Adrian and Enberg (1971), and
Johnson and Hartung (1974). The former study emphasized the importance of outward or
lateral rotation at the shoulder joint prior to the “forward movement” of the shoulder and
elbow, and the latter concluded that rotational movements of the lower arm were the key
elements to superior performance. A provocative article by Rantzmayer (1977) drew similar
conclusions to those of Poole in his dissertation.
The first in-depth biomechanical studies of badminton performance were carried out by
Gowitzke and Waddell, and were reported at the first international coaching conference held
in conjunction with the World Badminton Championships in Malmo, Sweden in 1977
(Gowitzke and Waddell, 1977; Waddell and Gowitzke, 1977). Kinematic analyses of
badminton power strokes were the major focus, and results contradicted that found in the
badminton literature, including manuals of sports governing bodies. An estimation of the joint
contributions made to the velocity of the shuttle in the badminton smash attributed 53% of
the final output to shoulder rotation and radio-ulnar pronation. The early research focused on
the overhead power strokes performed by Canadian nationally and provincially ranked
players. Later, the research included top international players. The myth of “wrist snap” was
reportedly laid to rest. Over the years, Gowitzke and Waddell (1979, 1980, 1986, 1989,
1990, and 1991), have presented research papers that expanded on the concepts related to
forehand and backhand clears and smashes. They also delved into other aspects of
badminton stroke production such as reaction and movement times, and physiological
measures of young badminton athletes.
Sakurai, et al (1989) studied cut and drop shots, providing perhaps the first attempt to
perform a three-dimensional analysis of some of the strokes employed in badminton. Their
results revealed the importance of radio-ulnar pronation, elbow extension, and wrist ulnar
deviation in the cut shot. In 1993, Lee compared standing and jump smashes, and found
jump smashes to produce superior racquet-head angular velocity and shuttlecock velocity.
In 1995, Tang et al provided a three-dimensional cinematographical analysis of the
badminton forehand smash, focusing on the forearm and hand. Luhtanen (1996) further
explored concepts related to the clear in junior badminton players. Tsai and Chang (1998)
studied smash and jump smash performances of elite and collegiate players and noted that
generally, elite players achieved greater angular velocity of elbow movement (taken to mean
radio-ulnar pronation), and the movement times (from preparation phase to point of contact)
were less than those of collegiate players.
Suffice it to say that all of the studies emphasized that, in performing power strokes, such as
the forehand clear, smash, or cut shot, the forearm action, anatomically described as
pronation of the radio-ulnar joints, played a predominant role in the success of the stroke.
The significant distinguishing action for backhand power strokes also lay with the forearm
action, and is technically called supination.
METHODS: The early research by the authors focused on the overhead power strokes
performed by Canadian nationally and provincially ranked players performing in the
laboratory. Two high-speed 16-mm cameras operating at 400 frames per second were used
to record the athletes’ movements as they played overhead clear and smash, forehand and
backhand. Kinematic analysis of the film revealed that the hypotheses of the investigators
on the biomechanics of stroke production were supported.
Subsequently, performances of world class players at Commonwealth Games and World
Championships were filmed and the results confirmed those of the earlier studies.
More detailed studies of badminton strokes were carried out by analyzing the ground
reaction forces of overhead power strokes by use of a force platform. Attention was focused
on the components of force in the vertical direction and was compared to the weighting and
unweighting phases of a vertical jump for height.

RESULTS AND DISCUSSION: Whether playing a clear or a smash, an elite badminton
player takes advantage of long resistance torque distances for rotational movements at both
the shoulder and radio-ulnar joints in order to produce the power needed in these strokes
with a minimum energy cost. After preliminary movements are used by a player to move the
racquet backward during the ‘wind-up’ phase of a stroke, a player will ‘move out from under
the arm’ by a combination of hip and trunk rotations. This is followed by accelerating the
racquet forward and upward principally by medially rotating the shoulder, and pronating the
radio-ulnar joints (Gowitzke and Waddell, 1977, 1979). In addition, it should be noted that
use of a flexed elbow during the shoulder rotation portion of the stroke, maximizes the
contribution of the shoulder action to the stroke. As well, a marked angle between the
racquet and the forearm maximizes the contributions of radio-ulnar pronation.
The term “power grip” was coined by Rantzmayer and Niesner (1987) and stemmed from the
recognition that the angle formed between the racquet and the forearm may be as large as
ninety degrees if the grip has the fingers well flexed and bunched together instead of a
‘shake-hands’ grip. With this grip, rotations at the shoulder and radio-ulnar joints move the
racquet head in an even larger arc than would be possible with the traditional grip.
Force platform studies revealed that all overhead power strokes were played with the body
elevated and the platform “unweighted”. For the forehand smash, for example, all players
were airborne and the feet were not in contact with the floor at impact, which supported the
observations of the authors that every smash is a “jump smash”. For all smashes, contact
with the shuttle was made during the last part of the unweighting phase while the body was
descending from its high point (Gowitzke and Waddell, 1980).
Whether playing forehand or backhand strokes, if the objective of the stroke is power, some
basic biomechanical principles emerge:
1. Employing sequential joint actions. A sequence of joint actions is employed, with the
larger more proximal muscles of the body initiating the action, and the smaller, more
distally located muscles following up through contact with the shuttle (Gowitzke, 1979;
Lee, 1993). This may be referred to as a whip-like action.
2. Making use of the backswing with continuous action . A continuous action from
backswing to follow-through should be stressed so that no discernible instant in time may
be specified as the time when the backswing stops and the forward swing starts. In
forehand overhead power strokes, for example, the following description summarizes the
action (Gowitzke and Waddell, 1977; 1979);
· The proximal joints, principally hip and intervertebral joints, rotate away from the hitting
direction first.
· While hip rotation reverses, intervertebral joints may still counter-rotate.
· The intervertebral rotation then reverses and commences in the hitting direction while
upper arm lateral rotation at the shoulder joint commences.
· As well, elbow flexion and radio-ulnar supination start.
· At the appropriate time, medial rotation at the shoulder commences, even while the
elbow and radio-ulnar action lag behind.
· Finally, elbow extension and radio-ulnar pronation occur.
The same description applies to backhand overhead power strokes except that the terms,
medial rotation, pronation, lateral rotation and supination, respectively, may be substituted for
the underlined words. Niesner and Rantzmayer (1982) referred to the continuous action as
“the loop” and stressed “there must not be any break between the preparatory movement
and the force-producing movement”.
3. Maximizing impulse while minimizing time . The ideal power stroke is one that maximizes
impulse (the product of force and time) by delivering a very large force over the shortest
possible time. A quick, but not necessarily long backswing is taken with no hesitation
between backswing and forward swing. This means that during the backswing, the
muscles that are about to be operative in the force-producing phase, are stretched. This
takes advantage of the elastic properties of muscle and inherent proprioceptive reflexes.
Badminton drives, that is strokes played in the area of waist height, have not been
researched. Generally, it is considered that in all drives the racquet head is higher than the
hand holding the racquet. Thus, there is a flexion of the wrist toward the radial side.
The authors suggest that biomechanically, the sequential actions are generally different for
strokes that are played above the waist as opposed to those played below the waist. On the
forehand side, strokes played above the waist generally are struck with the wrist flexed to the
radial side, and the forearm pronates during the stroke. When the shuttle is struck below the
waist, the racquet head is below the hand, the wrist is flexed to the ulnar side and the
forearm supinates during the stroke.
The reverse is true for the backhand side. In strokes played above the waist, the forearm
supinates and for those strokes played below the waist, the forearm pronates. These
observations and qualitative analyses are at odds with that found in the badminton literature.
PRACTICAL APPLICATIONS: The common question of coaches after listening and
observing biomechanical analyses of power strokes is “never mind the technical analysis –
how do I train my athlete to improve his(her) smash?” The question reveals the importance
of clarifying the nature of sport biomechanics and how biomechanical principles can be used
to assist coaches. From the practical point of view, for coaches, the development of power is
solely dependent on maximizing the joint actions in a sequential fashion.
Not having high-speed cinematography or videography on court poses a major problem for
coaches to analyze and correct or improve stroke production. Since the whole power stroke
takes place in about 1/10 second, the problem of observing the actions is very difficult.
Fortunately, the results of research provide a base for devising cues for coaches on what to
look for when coaching an athlete and how to improve his(her) stroke production.
When teaching the forehand clear or smash, it is a foregone conclusion that the direction in
which the racquet faces at contact with the shuttle is indicative of the direction in which the
shuttle will fly; i.e., upward for clear and downward for smash. However, the power for these
strokes emanates from the turning motions discussed in the results section.
Cues are devised to maximize the biomechanical actions of joints in the upper extremity,
since they are the most important and the most difficult to monitor because of the speed with
which they are carried out. The coach must be alert to catch the necessary “glimpse” of
racquet and/or arm position cues that designate the correct execution of overhead power
strokes on court.
Coaching cues:
1. From a position behind the player, at the start of the backswing, the coach should look for
the racquet to move upward ‘on edge’ – that is, so that the edge of the racquet is seen
rather than the ‘flat’ of the racquet. (This is a difficult cue and needs considerable
practice to recognize easily.) Near the top, when the racquet head is moving quickly, it
may be impossible to see that the racquet ‘face’ will turn toward the shuttlecock. In
viewing performance from the player’s racquet side, in the follow-through, when the
racquet is slowing down, the coach should look for the “flashing” of the ‘face’ of the
racquet for an instant, especially when the smash is being performed. The sequence of
the forehand action is as follows:
· Preparation: The wrist is radially flexed; the racquet shaft is at an angle with the hand to
the radial side of the forearm. The racquet head is ‘on edge’ to the hitting direction. The
preparatory position is maintained until the last instant before commencing the stroke.
· Backswing: The racquet is drawn back quickly, with the racquet head sweeping back
and down to the hitting side.
· Forward swing: The racquet head moves upward in the ‘on edge’ position when viewed
from behind the player. The elbow remains high during contact. A moment after the
shuttlecock is struck, the elbow is still high but flexed, the racquet head down, and the
‘face’ of the racquet is toward the observer when viewing from the player’s racquet side.
In powerful strokes, i.e., all smashes, the lower extremity on the hitting side is flexed at
the hip and carried forward as the stroke is completed.
2. It is safe to say that the backhand clear or smash is almost a mirror image of the
forehand strokes. The ‘end’ position of the forehand clear, for example, is the beginning
position of the backhand clear. And the ‘end’ position of the backhand clear is the
beginning position of the forehand clear. In both forehand and backhand strokes, a
significant feature to look for is the position of a high elbow, with the upper extremity well
abducted from the trunk. Therefore, from a position behind the player, at the start of the
backswing, a coach should look for the racquet to move upward ‘on edge’. In the followthrough,
from a position beside the player, the coach should look for the ‘flat’ of the
racquet, although it is only for an instant. The sequence of the backhand action is as
follows:
· Preparation: The preparatory position is identical to that of the forehand power stroke
with the racquet head ‘on edge’.
· Backswing: The racquet head is drawn quickly downward as the elbow moves sharply
upward and is best viewed from behind the player.
· Forward swing: As the elbow rises, the racquet is drawn up ‘on edge’ when viewed from
behind the player. As the elbow straightens, the elbow appears to stop or even back up
when viewed from the side of the player. As the stroke ends, after contact, the entire
upper extremity comes to an abrupt stop, as the racquet continues forward and exposes
the ‘flat’ of the racquet to an observer standing beside the player.
Awareness of the required sequential joint actions in power strokes as well as the ability to
use the cues to ascertain their presence do not in themselves provide the coach with the
knowledge to improve the stroke action and increase the power.
When the coach does not see views of the racquet position as described above, work has to
be done on these joint actions, commencing with the forearm actions. In an overhead stroke,
there should be enough power using only pronation on the forehand side and supination on
the backhand side to clear the shuttle from the back doubles service line to the back doubles
service line. This stroke should be practiced regularly using as little elbow extension as
possible. When satisfactory power has been achieved, elbow and shoulder action can be
built into the full sequential action chain.
When “controlled” power rather than full power is needed, only the terminal elements of the
sequential action may be required. For example, in performing an attacking clear, a player
may invoke deception by holding back on the use of hip and intervertebral joints, but invoking
to the fullest extent the use of the distally located joints and muscles in maximizing the
impulse to perform the stroke.
When training to improve badminton drives, important consideration should be given to
the turning of the forearm in both forehand and backhand strokes. For example, in
employing small weights, it is much more important to carry out pronation and
supination exercises, than to use wrist curls.
Lastly, the high singles serve is a power stroke and has been the main serve employed in
singles over the years. Recently, however, the short serve has been used extensively. It is
interesting today to see some of the international players using the backhand serve. And
why not; it is the most deceptive stroke by far. By making use of the power in pronation
action, short serves can be interspersed with “attacking clear” services to great advantage.
The serve becomes an ‘attacking’ shot and not the defensive stroke that it has been for so
long. The appropriate use of pronation of the forearm provides for power and deception in
the backhand serve.
GLOSSARY OF TERMS:
1. The following terms are used to describe racquet position relative to the view of the
coach:
· ‘On edge’ refers to viewing the racquet so that the strings cannot be seen.
· ‘Flat’ of the racquet refers to viewing the strings so that the entire circumference of the
racquet head can be seen.
· “Face” of the racquet refers to viewing the strings on the hitting side only.
· ‘End’ position refers to the follow-through position of the racquet immediately after impact
with the shuttle when its angular velocity has diminished toward zero.
2. The following terms are the anatomical terms used to describe actions at joints.
· Upper extremity – includes all bones, muscles, and joints of the upper arm, forearm, and
hand.
· Radial flexion — an angle at the wrist between forearm and hand so that the hand is
angled to the thumb side.
· Ulnar flexion — an angle at the wrist between forearm and hand so that the hand is
angled to the little finger side.
· Pronation – an action about an axis through the radio-ulnar joints so that the palm is
turned downward or backward.
· Supination – an action about an axis through the radio-ulnar joints so that the palm is
turned upward or forward.
· Medial rotation – an action about an axis through the shoulder joint so that the forearm
and palm are facing inward or downward.
· Lateral rotation – an action about an axis through the shoulder joint so that the forearm
and palm are facing outward or upward.

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