The rotational technique is more complex and requires more coordinated footwork. The purpose is to build up rotational inertia, which is maximized by using a long sweeping motion of the free leg. During the spin, the upper body is rotated opposite the lower extremities creating a wide hip shoulder separation. This builds torque by stretching the core muscles, which store potential energy to be transferred through the arm to the shot for release (14,31). In both the glide and rotational techniques, building energy through the lower extremities while keeping the body back creates the effect of loading a spring, the potential energy from which it is transferred as kinetic energy through the upper extremity and to the shot for release.
Electromyography performed during shot put showed that the activity of the vastus lateralis and pectoralis major muscles was correlated with performance after taking the power position, during the delivery phase (28). There is an inverse correlation between performance and time to reach peak triceps activity during the throwing phase (28).
The discus is 220 mm in diameter and weighs 2 kg for men and 181 mm and 1 kg for women. It is gripped with palm and fingers and thrown after several rotations as the athlete moves toward the front of a 2.5-m circle. The discus throw is broken down into five phases: initial double support, single support, flight, second double support, release, and delivery. Double support phase is the time between maximum backswing and right foot takeoff. This marks initiation of the traverse across the circle, where the trunk is rotated, loading the core muscles to optimize torque potential, and both arms are extended to provide counterbalance of the reduction in base support. This phase is followed by left foot take off as the body moves into single support on the right leg. The arms remain extended and the trunk rotated to promote maximum potential and kinetic energy as the right foot takes off and the body rotates. The body is then accelerated forward during flight phase. The thrower lands on the right foot, which plants and pivots. The body leans forward and knees are bent to lower the center of mass. The left foot then plants, moving the thrower into second double support phase where the body is perpendicular to the direction of the throw. Release phase is characterized by release of transfer of stored energy through the kinetic chain into the implement. The body rotates toward field first through the pelvis, then the trunk, the chest, and the throwing arm. The final release of the implement is known as delivery phase. Optimum release angle falls between 35 and 40 degrees.
The hammer is a 7.3-kg metal ball that is attached to a handle by a 4-ft steel wire for men (4 kg and 3 ft 11 in for women). The throw is more complex than other types of throws and is the only event where a centrifugal force is exerted on the implement via a wire and handle rather than with the hand directly. The throw begins with preliminary arm swings followed by several turns (ranging from three to five), and then release. Each turn has a component of both single and double support. During rotations, the wire is extending horizontally, allowing the hammer to rotate with a maximum radius, which produces maximum angular acceleration. The centrifugal force created by the rotation exceeds the weight of the thrower so maintaining balance is achieved by shifting the center of mass (19). Biomechanical studies have shown that the hammer can only gain acceleration during double support phases, thus coaches and throwers have sought to extend the duration spent in double support. In elite throwers, the most angular momentum is gained during the double support phase of the final turn (9). Important parameters to consider during hammer throw include angle of flexion of the knee and the relationship between angles of torque of the hips and shoulders (9) in terms of both their contribution to success of the throw and the stresses they put on the joints. Higher center of gravity and height of the hammer at release are associated with greater distance.
Javelin throwing technique consists of five major components: 1) approach—the thrower runs in the direction of the throw to build momentum; 2) a series of sideways crossover steps, stretching the trunk and throwing muscles; 3) phase of single support as the thrower transitions from running to throwing; 4) runner comes to an abrupt stop, transferring momentum from forward motion of body to forward motion of javelin in an overhead throwing motion culminating in javelin release; and 5) follow through where the thrower decelerates the throwing motion and regains balance (18). The kinetic chain activation pattern in javelin throw follows a pattern similar to that of a baseball pitcher and includes stride, pelvis rotation, upper torso rotation, elbow extension, shoulder internal rotation and wrist flexion (8). During the cocking phase of the throwing motion, the arm is abducted and externally rotated, causing high anterior translational forces on the glenoid (17). These forces are resisted by stabilizers that include the glenoid labrum, the glenoid ligaments, and the anterior joint capsule. Dynamic stabilization is provided by the muscles of the rotator cuff along with the long head of the biceps tendon (30). The follow through phase generates the greatest muscle contraction and joint forces after the release of the implement; all muscle groups are active as eccentric contraction of muscles slows down the arm. Joint loads are the greatest during this phase with high compressive, posterior and inferior shear forces, as well as adduction and horizontal adduction torque (17).
Joint Stresses and Injuries
Throwing events share common injures due to their similarities; however, the unique features of each event put athletes at risk for distinct injuries. All throwing athletes are susceptible to injuries of the rotator cuff due to the repetitive stress through the shoulder and the requirement of the rotator cuff tendons to stabilize the joint throughout explosive movements. Anatomical features of the tendons themselves contribute to injury. Tendons under stress require the robust activity of tenocytes to replenish their collagen and matrix proteins. Additionally, muscles and tendons need a blood supply adequate to maintain tenocyte production. Studies of the muscles and tendons of the rotator cuff have shown that there are certain areas that consistently receive relatively poor blood supply and thus, are more susceptible to injury (24). The insertion point of the supraspinatus is a relative watershed area that makes it a site of potential injury (24) for all throwers.
Javelin throw in particular has been studied extensively for its effects on the shoulder due to its similarity to the overhead baseball pitching motion. While their precise motions vary, all of the throwing events impose abduction and external rotation forces on the shoulder. During the extreme external rotation and abduction of the shoulder, significant forces are transmitted through the muscles and tendons of the rotator cuff. The supraspinatus, infraspinatus, teres minor, and latissiumus dorsi are most active during the most abducted and externally rotated phase of throwing (12). Deceleration of the arm after release also requires the rapid and forceful contraction of these same muscles to resist distraction, horizontal adduction, and internal rotation. Acutely, these extreme forces can lead to inflammation and over time can lead to chronic, degenerative changes (17). Adaptive changes occur in the throwing arm of overhead throwing athletes including increased external rotation range of motion, decreased internal rotation range of motion, hypermobility of the anterior joint capsule, hypomobility of the posterior joint capsule, and increased capsular laxity (5,17,30). The glenohumeral joint capsule under repetitive load becomes loose anteriorly and tight posteriorly. As the external rotation increases, there is increased stress on the glenoid ligaments, primarily the inferior glenohumeral ligament, leading to anterior and superior translation of the humeral head. This leads to a subtle subluxation that has been proposed as the primary mechanism of shoulder pain in throwers, as opposed to primary impingement (10). Muscles outside the rotator cuff also are at risk of injury. Shot putters are at risk of pectoralis major strains due to their explosive activation before release.
Elbow joint injuries are relatively unique to javelin and are less common in shot put, discus, and hammer throw. The elbow joint is subject to significant valgus force during the overhead javelin throw. Valgus forces are highest in the phases of late cocking and early acceleration when the shoulder is externally rotated and the elbow is flexed. As the trunk begins its rotation, the elbow acts as a fulcrum between the rotating trunk and the implement in the thrower’s hand. The anterior bundle of the ulnar collateral ligament (UCL) resists valgus stress on the elbow while the elbow is flexed from 30 to 120 degrees. Repetitive near failure stresses on the ligament during javelin throw can lead to microtrauma within the UCL (4). As the UCL breaks down to these repetitive forces, there are consequent downstream effects on the other structures of the elbow. The flexor and pronator mass, most notably the flexor carpi ulnaris and the flexor digitorum profundus, act as dynamic stabilizers of the elbow during valgus stress. These muscles also are prone to injury along with UCL insufficiency (4).
Additionally, due to the valgus stress at the elbow, the ulnar nerve experiences significant stresses during the throwing motion, reaching its mechanical and circulatory limits (1). Any additional instability can potentiate the forces on the ulnar nerve and lead to a traction ulnar neuropathy at the elbow.
The implements (with the exception of the hammer) are held in the fingertips, and upon release, there is extension of the wrist and long fingers. This can result in hyperextension injuries of the long fingers if release technique is not optimal. Volar plate injuries are possible with long finger hyperextension. Typically, this occurs at the proximal interphalangeal joint resulting in full or partial volar plate rupture with or without an avulsion fracture (21). There may be concomitant collateral ligament injuries as well. Because of the loss of volar stabilization of the joint, the unequal contribution from the extensor tendons may pull the joint into an extension deformity (16). Shot putters also are particularly vulnerable to injuries of the wrist. The wrist carries the weight of the shot in an extended position. As the release is a “push” rather than a throw, the wrist is required to produce a forceful flick. Both acute and chronic injuries can result from this. Acute injuries include strains and tears of the wrist flexors. With repetitive wrist extension, friction develops between the intersection of extensor tendons of the thumb and wrist, leading to tenosynovitis of the tendon sheaths known as intersection syndrome.
All of the athletics throwing events involve hyperextension and rotation of the lumbar spine, leading to greater than normal loads on the axial structures. This predisposes throwing athletes to muscle strain of the core and lumbar musculature as well as chronic degenerative changes that develop over a career of repetitive stress. Shot putters and discus throwers have a significantly higher rate of osteophytes in the lumbar spine compared with all other track athletes. In radiographic studies, javelin throwers had the most radiographic changes compared with all other track events, followed by shot put and discus throwers (26). Spondylolysis and spondylolisthesis are more common in retired javelin throwers than in the general population (25). Radiographic findings do not always correlate with pain; however, back pain is a major, debilitating problem among athletes and the general population. If participation in throwing events early in life contributes to degenerative changes down the road, further study into causative factors and efforts toward prevention is warranted.
Rotary movements, such as those in shot put, discus, and hammer throws, impose forces on the knee that can lead to injury. The rotational movement of the trunk needs to be in perfect coordination with the rotation of the lower extremities to avoid placing excessive rotary force on the knee. Landing after a flight phase in discus and shot put is also an injury prone position; if the foot is not planted properly, twisting of the knee and ankle can occur. Meniscus and anterior cruciate ligament tears are most likely to occur with this mechanism. As mentioned above, a survey study of British shot putters found that ankle injuries were the most commonly reported type of injury (3). The physical boundary of the throwing circle can itself create an opportunity for injury. In shot put during approach into power position and release, while the athlete is moving forward at high velocity, the toe board can be used as a break for the lead leg, imposing inversion and rotational forces on the ankle. Additionally, the repetitive stress of these frequent impacts can lead to microtrauma in the ankle as well as the small bones of the foot, which could eventually lead to osteoarthritis of the ankle and midfoot.
The cornerstone of injury prevention in throwing events is developing and maintaining proper technique. To throw a heavy implement a great distance requires inordinate strength, balance, coordination, timing, and flexibility to generate sufficient torque and power. The high degree of technicality that is required necessitates extensive training to develop proper and safe technique. Because repetitive stress injuries are common among throwers, minimizing the number of repetitions during training would minimize injuries. However, as described, the technical nature of these events requires consistent practice and repetition. An appropriate balance must be achieved between practicing to achieve consistent form but minimizing repetitions to prevent overuse. An argument could be made for athletes to train at submaximal performance to mitigate overuse injuries, thus minimizing the magnitude of force through the joints during noncompetitive throws.
The essence of being a successful thrower is maintaining the flexibility to withstand difficult positions while preserving the strength to generate torque and leverage. Throwers must assume unusual positions, such as the power position in shot put, which require tremendous flexibility to perform properly. Thus, it is imperative that flexibility programs be consciously incorporated into training programs for throwers. Flexibility training should focus on shoulder internal rotators, hip flexors, hamstrings, and abdominal rotators. Dynamic stretching is preferable to static exercises.
In a study of UK track and field athletes, the presence of a coach during both training and competition is a protective factor against injury (3). This highlights the importance of proper technique; real-time feedback from a coach promotes the maintenance of previously learned skills.
Proper equipment is essential for injury prevention in throwing events. Foot plant is critical to maintain biomechanics, particularly in throwing styles involving rotation. Appropriate footwear and playing surface are imperative to ensure proper foot plant. The surface for all throws should be flat and dry to avoid slipping or sticking which may alter the angle of ground reaction force imposing undesirable forces on the joints.
Success in throwing events is based on muscle power performance. Studies have demonstrated a correlation between muscular strength and performance in throwing events (7). Thus, throwing athletes spend a significant portion of their time strength training. While beneficial to their ultimate performance, this provides yet another opportunity for injury. Often, the objective of the exercise is to grossly approximate the muscular activations that are required for the event. To accomplish this, many throwers focus on Olympic weight lifting. These are explosive, yet controlled movements with a weighted implement, similar to those required for shot put, hammer throw, discus, and javelin. Muscular and ligamentous strains account for 46% to 60% of acute weight lifting injuries (15). Severe acute injuries include disc herniations, joint dislocations, fractures, and tendon ruptures. Tendinopathies are the most common chronic strength training injury. Chronic weight training injuries can result from repetitive high stresses with insufficient recovery time. This can be a result of over training, either in frequency or intensity, or of increasing intensity too quickly (15). Prevention should be focused on a weight training regimen with emphasis on proper technique and allowing sufficient recovery time. Strength and conditioning coaches are encouraged to research and implement periodization principles to achieve peak performance and minimize injury (29). These principles use the structured variation of training methods and volume loads to achieve performance goals at designated times throughout the season. Two phases are described: general phase encompassing strength endurance and general strength training, and competition phase emphasizing power and speed with a brief taper before elite events (13).
Finally, special attention must be paid to high school athletes who may not have access to experienced throwing coaches. While it is common knowledge that athletes need to gain strength to become a successful thrower, there is not enough knowledge about strength and conditioning technique. Appropriate age-based plyometric routine, at an appropriate frequency, is essential to injury prevention in young athletes.
Throwing events in track and field require a combination of strength, flexibility, precision, and focus. An intact kinetic chain is critical for success in these events, which require activation of multiple muscles groups throughout the body. The kinetic chain involves transfer of energy from the lower extremities, through the trunk, into the arm, and finally to the implement upon release. Throwers are susceptible to injuries of the shoulder, elbow, hand, wrist, fingers, back, knee, and ankle. Throwing events require significant strength and flexibility and thus, athletes spend a substantial amount of their time in the gym participating in strength training and plyometric programs. Thus, injury prevention must exist in a continuum from the gym to the throwing circle. The cornerstone of prevention in throwing injuries is practicing and competing with proper technique. Finally, there is a paucity of data reporting specific injury type, rate, and mechanism of throwing injuries. This highlights the need for more studies to characterize these injuries to help sports physicians develop evidence-based protocols for diagnosis, treatment, and prevention.
The authors declare no conflict of interest and do not have any financial disclosures.
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