This is an excerpt from Track & Field Coaching Essentials by USA Track & Field.
Skills of the Throwing Events
Success in the throws depends on the consistent performance of skills and techniques. Some of the skills required for throwing may seem unnatural at first. The summation of all forces leading up to the release of the implement directly affects the throw. Although the throwing events are similar in some aspects, the movements that lead up to the release may vary.
The shot put consists of three movements: the glide or rotation, the standing power position, and the release. Movements involved in the hammer and discus include body rotation within the boundaries of a ring and rely on centripetal forces and torque, culminating with a release. Unlike the hammer and discus, the javelin requires the athlete to build speed over a linear distance. A successful throw in any of these four events requires the transfer of explosive strength and maximal muscular force onto the object in the shortest possible time.
The importance of muscular strength drives the requirement for throwers to develop leg strength in the early stages of their careers. Strength is so important for a thrower that it often becomes a limiting factor in technique development. Weaker athletes simply cannot develop and refine technique as quickly or effectively as stronger throwers can.
Consistent Implement Acceleration
Although mechanics are important, rhythm is equally important for quality throws. Proper acceleration is a key component of rhythm. For example, the final action of shot-putting in the direction of the throw starts when the rotation of the hips and shoulders stops. At the end of the rotation of the hips and shoulders, the velocity of the shot is just over 6 m/s. After the throwing arm has taken part in the release action through the extension of the elbow and shoulders, the shot velocity increases to just under 7 m/s. The acceleration of the implement must be consistent and positive. The idea of a consistent, progressive acceleration seems simple, but it is often violated. A common error is accelerating the implement too quickly only to decelerate it later. Progressive acceleration is important in both the preliminary movements and the delivery. On a graph, the acceleration rate should map as a gradual curve, without large spikes and dips.
Summation of Force
Force generation normally begins in the proximal joints. The large muscles of the legs and torso initiate the movement and overcome inertia, so that the smaller muscles of the shoulders and arms can further increase the velocity of the implement in the delivery phase. The initial force generated by the proximal-to-distal sequencing of hip extension, knee extension, and plantar flexion accelerates the athlete-and-implement system. This force must be transmitted to the ground or to an implement through other (distal) joints. For example, although the shoulder (proximal joint) may be producing the force, the force is being transmitted to the shot put through the elbow and wrist (distal joints). Upper-body activity in the delivery and arm strike results from a summation of forces. Although throws differ slightly, proximal-to-distal firing must be preserved. Overall, an optimal coordination pattern appears to be one in which muscle activation and segment acceleration occur in a proximal-to-distal manner with an optimally timed deceleration of body segments leading up to the moment of release.
One of the benefits of a proximal-to-distal coordination pattern is that it generates a whiplike motion. When the upper leg and trunk musculature are the first to contract, greater separation is developed between the shoulders and hips. This results in a whip effect as the hips decelerate and the shoulders accelerate as they uncoil and the implement is released. This deceleration of the hips is critical in an acceleration - deceleration coordination pattern. If the extremity muscles are strong but the core is weak, an adequate summation of forces cannot be created. The result is often technical breakdown and a less-than-optimal performance.
Lengthening the Path of Implement Acceleration
The longer force is applied to the implement, the greater the momentum and velocity will be. To lengthen the amount of time force is applied, the athlete must achieve maximal length in the path of the implement during the delivery. Two ways to lengthen the acceleration path are weight transfer and turning, or using closed throwing positions.
During the delivery phase, body weight is transferred from the back foot to the front foot to increase the body's range of movement and the path of the implement. This transfer of body weight is a crucial component of the throw. The front leg should extend almost completely at the moment of release. However, the timing of initiation and the magnitude of the action of the lower extremity differ considerably between the glide and rotational techniques. Unlike in the glide technique, in the rotational technique the workload is more evenly distributed between the legs during delivery. That is, instead of an initial push with the rear leg and a weight transfer to the front leg, rotators push more simultaneously with both legs.
After arriving in the power position and during the delivery, the center of mass (proximal joints) of the body turns smoothly and progressively in the direction of the throw. This turning, or rotation, is a crucial component of the throw. The body is turned away from the direction of the throw in the start and power positions, enabling it to turn through a greater angle as the implement is delivered. For more advanced throwers, a slight forward lean of the trunk while in double support helps to maintain balance when the angular velocity of the body is reduced and the absolute velocity of the implement is relatively high. A thrower of shorter stature can take advantage of a longer radius, which allows for a smoother change of kinematic indicators.
Important implications are associated with producing a larger radius in the early parts of the throw. For a given linear speed, a larger radius provides a system that allows the thrower to rotate with a slower angular velocity. A slower rate of rotation permits slower contractions of the muscles involved, which allows these muscles to exert larger forces. This is due to the force - velocity relationship for skeletal muscle. In turn, a larger muscle force results in a larger torque and an increase in the overall angular momentum of the system. Therefore, using a longer radius in the early parts of the throw increases the angular momentum of the system and lengthens the path of the implement.
Separation and Torque
Although the body turns smoothly and progressively in the direction of the throw, in most situations the upper body and lower body do not turn from the same positions at the same time. This is called separation, referring to the separation between the hip and shoulder about the rotational axis. In addition, throwers generally start to turn the lower body before turning the upper body. This twists the core of the body and creates torque. Force is a push or a pull that changes the linear state of motion of an object or body. The angular equivalent of force is torque. Torque is the turning effect created by a force about an axis. Torque can be increased either by applying greater force or by increasing the radius of rotation. When the upper leg and trunk musculature are the first to contract, greater separation occurs between the shoulders and hips. As the hips decelerate and the shoulders accelerate as they uncoil, the implement is released; this separation results in a whip effect. Separation and torque exist in different degrees in the various throwing events. Both serve to establish a summation of rotational forces, beginning with the lower body and finishing with the upper body.
The thrower must eventually stop the momentum created in the body to transfer it to the implement. A good way to do this is to harmoniously blend the left-leg block and the left-arm block. The blocking actions of the upper body in the shot put, discus, and javelin differ slightly based on the unique release mechanics of these events. For example, in the discus, the throwing arm is ideally 90 degrees from the body to maximize radius. The left-side block would be initiated and positioned opposite and equal to the throwing side.
In the left-leg block, the left leg plants firmly in the power position with the left heel pushing into the ground and stopping the horizontal and rotational movement of the left side of the thrower's lower body. This action transfers momentum to the upper body and implement. Proper alignment of the feet is essential to proper blocking. A common error in the shot put, discus, and javelin is to put the left leg too far left of center making blocking impossible. The error of planting the left foot too far to the left is commonly called being in the bucket.
During the delivery phase, the athlete has a long left arm to slow the rotation of the upper body, creating an eccentric stretch of the upper-body musculature and allowing the hips to fire ahead of the upper body. The shoulder girdle movement is a key factor in throwing performance. The left arm begins to shorten at the midline of the body to create a forceful shortening and summation of forces.Desired forceful contractions in athletic endeavors usually are elastic and reflexive, setting up a powerful response of eccentrically stretched muscles, referred to as a volitional concentric response. If the volitional contractions are improperly timed or voluntary involvement by any muscle group is too great, the elastic energy generation of the entire system is diminished, reducing efficiency. The left arm remains long until delivery is initiated, at which time it moves in close to the side of the thrower to help stop the left side of the upper body and transfer momentum to the nonthrowing side. The action of throwing occurs much more efficiently when these stretch reflexes are invoked and elastic energy is developed.
When teaching athletic techniques, coaches should create situations that prestretch the muscles. The hammer is an exception to this rule because it is thrown with both arms. However, on release, the left side of the hammer thrower blocks as the thrower attempts to maximize radius and lift the implement.
As in many athletic disciplines, posture is an important component of throwing events. Because the core is at the center of nearly all sport movements, the core musculature is a key element of energy generation. The torso's ability to support effective arm and leg actions (core stability) is essential to performance and injury prevention in many sports.
Postural integrity is directly linked to elastic energy generation. Body parts must be stabilized in proper alignment for applied forces to produce displacement without excessive distortion and rotation. Excessive instability or postural misalignment cause postural muscles to overwork to compensate and maintain balance, which restricts their ability to function elastically. However, the postural unit should not be stabilized in a way that restricts movement. Proper posture during athletic endeavors should not be associated with total rigidity, which compromises elastic energy production. Proper alignment of the core of the body is important for movement efficiency and injury prevention.
An important element of posture is head alignment, and it is important in throwing events for several reasons. Improper head alignment affects the technical execution of a skill by impairing limb function. Balance may also be affected, because most of the body's vestibular equipment is disturbed. Finally, the head is quite heavy, so extraneous movements may produce instability. Improper alignment may cause instability, which can elicit stiffening, multilink, or grounding strategies and interrupt the technical flow of the throw, causing inconsistencies in performance. Proper alignment of the head ensures relaxation and balance and helps create a good release or arm strike. Dropping the head and turning the head away during the throw are common errors.
Another component of posture, pelvic alignment, is also crucial for efficient throwing. Pelvic misalignment significantly affects the function of the legs and nearly always produces instability. The instability resulting from pelvic misalignment also elicits harmful stiffening, multilink, or grounding strategies, which disrupt throwing technique. A neutral alignment of the pelvis with respect to the spine promotes relaxation, proper leg function, and good turning. Excessive bending at the waist after arriving in the power position, a common mistake, places the pelvis in an inferior position.