the Overarm Throw
To give the reader a better understanding of the coordination
pattern referred to as sequential segmental actions, the force phase
of the overarm pattern is analyzed as applied in a forceful throw such
as in pitching. This analysis includes joint actions, muscle activity,
and mechanics for the upper extremity only.
The purpose of the backswing, or preparatory, motion is to place
the segments in a favorable position for the force phase. There
are many ways to execute the backswing while taking advantage of
the stretch-shortening characteristics of muscle. Although some
favor one method over another, any windup is appropriate that places
the segments in the most advantageous position to maximize the number
of segments and the time over which force can be applied. Such a
windup, allowing the joints to be placed in an optimal position
to involve the greatest number of segments, includes pelvic and
trunk rotation in the opposite direction from the intended throw
(right for a right-hander), horizontal abduction, and lateral rotation
at the shoulder joint with elbow flexion and wrist hyperextension.
This sequence of arm action continues as a forward step is taken
with the opposite foot. This hand–foot opposition permits
the greatest range of motion in the trunk and pelvis. It also allows
for a large base of support over which the force phase can be applied
while preserving balance.
No pause occurs between the windup and the force phases. The
windup ends with a forward stride using the opposite leg. Establishment
of a base of support is followed immediately by pelvic and then
trunk rotation, accompanied by lateral flexion to the left (right-handed
pitcher). The trunk motion causes increased horizontal abduction
with continuing lateral rotation at the shoulder joint. Elbow joint
extension is followed by the initiation of rapid medial rotation
at the shoulder joint, forearm pronation at the radial–ulnar
joint, and then flexion and often ulnar flexion at the wrist joint.
The force phase ends with the release of the ball. The angle at
the elbow joint at release is approximately 105 degrees. The follow-through
includes the actions from ball release until the momentum developed
in the arm can be safely dissipated as the arm continues across
the body in a downward direction. In addition, a forward step is
also often used.
These actions proceed from the proximal (more massive) to the
distal (lighter) segments. In characteristic sequential patterns,
subsequent segments lag behind those preceding them. The subsequent
segment is carried along, lagging behind until the more proximal
segment attains its maximum angular velocity. The distal segment
then accelerates because of a combination of the series elastic
components, stretch reflex, and muscular contraction. This combination
results in the reaction or slowing down of the preceding segment.
Because of conservation of momentum, momentum (mv)
is transferred from the more massive (proximal) to the less massive
(distal) segments, significantly increasing their velocity. Therefore,
the linear velocity at the end of the chain—that is, the ball
at release—often can be over 90 miles per hour.
The legs play an important role in any successful throw. They
provide the stable base over which the trunk and other segments
act. In addition, the thrust they provide contributes significantly
to the force of this movement. The transfer of momentum from proximal
to distal, however, focuses the attention on the musculature of
the upper extremity. Because this phase emphasizes the application
of the force accelerating the limb, muscle contractions are mainly
concentric preceded by a short eccentric phase because of the lagging
of the distal behind the proximal segments.
of Upper Extremity (Table 18.2)
The lateral rotation preceding the medial rotation of the right
shoulder joint is controlled by the eccentric contraction of the
medial rotators of the humerus followed by the concentric contraction of
the same muscles, including the subscapularis, pectoralis major,
and latissimus dorsi muscles. During the acceleration phase, the
height of the humerus was controlled by a static contraction of the
middle deltoid. The deltoid and supraspinatus muscles contract concentrically
during the backswing to position the upper arm, and eccentrically
during the follow-through to help decelerate the arm. The infraspinatus
muscle was also very active (eccentric contraction) to assist in decelerating
the arm during the follow-through.
Table 18.2 Acceleration
Phase (Initial Portion of Force Phase) of the Overarm Throw ||Download (.pdf)
Table 18.2 Acceleration
Phase (Initial Portion of Force Phase) of the Overarm Throw
|Joint||Joint Action||Segment Moved||Force for Movement||Muscles Active||Kind of Contraction|
|Shoulder joints||Horizontal abduction||Upper arm||Muscle||Posterior deltoid||Concentric|
|Shoulder girdle||Abduction||Scapula||Muscle||Serratus anterior||Concentric|
|Wrist||Flexion||Hand||Muscle||Flexor carpi radialis||Concentric|
|Flexor carpi ulnaris|
|Flexor digitorum superfi cialis|
The biceps brachii muscle activity reaches its peak as the elbow
joint is flexed late into the backswing and at the beginning of
the force phase. Marked activity again appears during the follow-through
to protect the elbow joint in decelerating the forearm. The latissimus
dorsi muscle, active during medial rotation, remains active eccentrically
contracting during the follow-through to assist in controlling the
arm motion across the body.
It is clear that the stretch reflex is an important facilitating
mechanism in helping accelerate the lagging distal segment at the
appropriate time. The more rapid the stretch (eccentric contraction), the
greater will be the facilitating effect on the resulting concentric
contraction of the same muscle. In this way, forces can be summated
more appropriately. To gain the greatest facilitation from the stretch
reflex, there should be no pause between the windup and force phases.
Because the trunk rotates under the stationary head (eyes focused
on the target), the tonic neck reflex may facilitate the strong
acceleration occurring during the force phase. The asymmetric tonic
neck reflex facilitates the shoulder abductors and elbow extensors
on the chin side. This is precisely the arm position at release.
The extensor thrust reflex may act on both the upper and lower
extremities. Increasing pressure on the palmar side of the hand
as the arm is being accelerated forward may facilitate the arm extensor muscles.
Similarly, as the weight is transferred to the forward foot, the
pacinian corpuscles are stimulated by the increased pressure, resulting
in a facilitation of the lower-limb extensor muscles. When accuracy
is a factor, knee flexion must be maintained to flatten the arc
through which the hand is carried. This flattening permits the tangential
flight path of the ball to have a broader margin for error in the
timing of the release while arriving at the same target point following release.
the Forehand Drive in Tennis
The forehand drive (Figure 18.7) is one of the fundamental strokes
of tennis. Its objective is to send the ball over the net and deep
into the opponent’s court close to the baseline.
The forehand drive. From V. Braden and B. Bruns, Tennis for the Future. Copyright © 1977
Little, Brown, Boston.
The player faces the net with the feet about shoulder-width apart
and the weight on the balls of the feet. The racket is held with
an eastern or shake-hands grip.
The player pivots the entire body so that the shoulder and hips
of the nonracket side are toward the net. At the same time, the
racket is taken back at shoulder level in either a straight or a
circular manner, with the head of the racket above the wrist and
its face turned slightly down. The weight of the body is over the
rear foot (racketside).
The player flexes at the knee joints to drop the racket and racket
arm below the intended contact point (still keeping the racket head
above the wrist with its face turned down) and steps toward the ball
with the nonracket foot. The pelvis and spine rotate so the trunk
faces forward, and the weight is shifted to the forward foot as
the racket is swung forward and up. The racket face is perpendicular
to the court at ball impact, thus imparting topspin to the ball
as it swings through and up. The follow-through continues toward
the intended target, with the racket arm swinging across the body
and up toward the chin.
The action in the forehand drive is ballistic in nature and,
as such, is initiated by muscular force, continued by momentum,
and finally terminated by the contraction of antagonistic muscles.
The chief lever participating in the movement consists of the arm,
trunk, and racket together with the fulcrum located in the opposite
hip joint (see Figure 13.19), the point of force application at
a point on the pelvis that represents the combined forces of the
muscles producing the movement (mainly the gluteus medius and minimis
and the adductor magnus), and the resistance point at the center
of gravity of the trunk–arm–racket lever. At the
moment of impact, however, the resistance point may be considered
to be the point of contact of the ball with the racket face. The
additional lever actions that are due to the rotation of the spine,
the horizontal adduction at the shoulder, and flexion at the wrist,
if present, should also be recognized.
Another important anatomical factor is the strength of the muscles
responsible for keeping the arm abducted and for assisting in the
forward swing as the arm is carried along by the rotating spine
and pelvis. Those whose muscles lack the strength to swing the outstretched
arm with speed are likely to flex the arm at the elbow or adduct
the arm, bringing the racket closer to the trunk and thus shortening
the resistance moment arm. Among the muscles that were tested by
Van Gheluwe and Hebbelinck (1986) and found active in the forward
swing of the forehand drive were the anterior deltoid, pectoralis
major, latissimus dorsi, biceps, brachioradialis, and triceps, the
latter in two short bursts, the first at the moment of impact, and
the second during follow-through (Table 18.3). The erector spinae,
external oblique, and rectus abdominis are also active, with the
erector spinae most active (Knudson and Blackwell 2000).
Table 18.3 Anatomical
Analysis of the Forehand Drive in Tennis ||Download (.pdf)
Table 18.3 Anatomical
Analysis of the Forehand Drive in Tennis
|Joint||Joint Action||Segment Moved||Force for Movement||Muscles Active||Kind of Contraction|
|Trunk||Left rotation||Trunk||Muscle||Erector spinae|
|Right external oblique|
|Right shoulder joint||Horizontal adduction||Upper arm||Muscle||Anterior deltoid||Concentric|
|Right shoulder girdle||Abduction||Scapula||Muscle||Serratus anterior||Concentric|
The purpose of the forehand drive is to return the ball so that
it will not only land within the opponent’s court but also
will land in such a place and manner that it will be difficult to
return. For the player to achieve this requires both high speed
and expert placement of the ball. Hence, imparting maximum speed
to the ball and, at the same time, placing it with accuracy are
the two major skills that the player seeks to develop.
The force of impact is determined by the speed of the racket
at the moment of contact with the ball, and maximum velocity can
be obtained only when maximum distance is used for accelerating.
The function of the backswing is to provide this distance. There
are two types of backswing, the straight and the circular. The straight
backswing has the advantage of greater ease in controlling the direction
of the racket and in timing the movement but the disadvantage of
necessitating the overcoming of inertia to reverse the direction
from the back to the forward swing. On the other hand, the circular
backswing permits the arm to move in one continuous motion over
a longer path, thereby providing more than twice the distance for
building up momentum. For the more skillful player who is able to
control both the direction of the racket and the timing of the entire movement,
it is the more efficient method.
In considering the force involved in the forehand drive, it is
important to distinguish between the force applied to the lever
and the force applied by the lever to the ball. Whereas the force
applied to the lever is muscular force, the force applied to the
ball is the force of momentum. It is determined by both the mass
and velocity of the implement that makes contact with the ball.
These, in turn, are related to the distance of the point of contact
from the fulcrum—in other words, the length of the temporary
resistance arm of the lever (“temporary” because
the distance from the fulcrum to the point of contact with the ball
constitutes the resistance arm of the lever only for the brief moment
of impact). In addition to the rotary movement of the trunk–arm–racket
lever, the linear motion produced by the forward movement of the
body (because of weight shift) adds to the force that meets the
Starting with the pelvic rotation and weight shift and working
out toward the racket, each movement in turn gets under way before
the next one commences. If the timing is correct, the cumulative
effect of these movements is to produce maximum velocity. If any
of the movements is added to the preceding one either too early
or too late, the potential velocity will not be realized.
Other important factors that contribute to the force applied
to the ball, and therefore to the speed of the ball on its return
flight, include the following:
- 1. The use of the arm in an almost fully extended position
increases the length of the lever, thereby giving greater linear
velocity to the racket head than would be the case if the upper
arm were close to the body. This is only true, however, if the racket
can be moved with the same angular velocity in both positions.
- 2. The effort needed to resist the force of the ball hitting
the racket is less when the racket lever arm is shortened.
- 3. It takes less time to swing a shortened racket lever into
the striking position than it does a fully extended one. (These
first three related factors help explain why beginners and children
bend the forehand elbow or choke up on the racket handle.)
- 4. The concentration of mass at the level of the shoulders
moving forward at the moment of impact ensures maximum speed for
- 5. A skillful player tends to use a relatively heavy racket
because, other things being equal, the greater the mass of the striking
implement, the greater the striking force (momentum) and, hence, the
greater the speed of the struck ball.
- 6. A new ball and a well-strung racket ensure a good coefficient
of restitution (elasticity), thereby increasing the speed of the
- 7. The bending of the knees at the beginning of the forward
swing followed by the extension of the legs and shift of weight
as the racket is swung forward and up increases the ground reactive force
imparted to the body and thus to the ball.
- 8. It has been generally accepted that a firm wrist and grip
are essential for maximum impulse to be applied by the racket to
- 9. Placement of the ball is a matter of direction. It will
be recalled that the direction taken by a struck ball is determined
by four factors:
- a. The direction of the striking
implement at the moment of impact.
- b. The relation of the striking force to the ball’s
center of gravity—in other words, the control of spin.
- c. Firmness of grip and wrist at the moment of impact.
- d. Angle of incidence.
The first of these factors is obvious. The beginner may be less
aware of the importance of the other three. For successful placing
of the ball, an understanding of the effect of spin and the skill of
imparting the desired spin to the ball are essential. Firmness of
grip depends on wrist and finger strength and is closely related
to the angle at which the racket face makes contact with the ball. Because
the angle of rebound equals the angle of incidence (actually slightly
less than this in the case of tennis balls because of their compressibility),
it will be seen that firmness of grip is therefore an important
factor in the direction taken by the struck ball.