Sports Science: Throwing

In all four throwing events the distance obtained is dependent upon the speed, the angle of release of the missile, and, in the discus and javelin events, certain aerodynamic factors.

Speed

An efficient throwing technique is one in which the athlete exerts the forces of his entire body over the greatest range practicable and, therefore, for the longest period of time; for the speed of release in throwing is proportional to the average force exerted through the implement’s Centre of Gravity. Other things being equal, the greater total body force produces the greater speed and the longer throw, since force = mass x acceleration the forces must be exerted against the missile in the proper direction, however—so far as practicable, in the direction of the ultimate throw; for the total effective force in throwing is the sum—the resultant—of all the components of the various body forces acting in that direction. As a general rule, in throwing, however, in the preliminary movements there is more horizontal drive than lift, and in the delivery more lift than horizontal drive. The eventual effect is to release the missile at an appropriate angle to the horizontal.

These two principles are fundamental to correct preliminary movement in throwing—in the run-up, glide or turns. In good throwing they are exemplified in the stretching and powerful recoiling of large muscle-groups; in the driving of body weight from one leg to another and (in the hammer and discus events in particular) in the use of maximum radius of movement in the turns and delivery.

The various forces of the body should be exerted in definite sequence and with proper timing; for the release speed in a good throw will be greater than in a bad one, even if the same effort has been expended and the throws are equal in all other respects.

From a purely mechanical point of view it is immaterial in what order a given set of forces is applied, one by one or simultaneously; the final speed is the same. To accelerate a shot, discus, javelin or hammer, however, each body lever in turn must be capable of moving faster in a given direction than the missile is moving in the same direction; and the faster the lever can move the greater will be its effective force.

In a summation of throwing forces, therefore, the levers of the body should operate so that each can make a maximum, or very near-maximum, contribution to speed. Hence the use of slower but more forceful muscles and levers first (i.e. of the trunk and thighs); while the faster but relatively weaker joints (i.e. of the arms, hands, lower legs and feet) exert their forces after the missile has developed considerable speed. While the feet and hands transmit force during the earlier movements, therefore, their own smaller forces are added only towards the end of a throw. It is important that each lever, having attained top speed, should continue at that speed in support of the movements which follow , bringing about not only a summation of forces, but a summation of rotations, too.

However, there must be no undue delay in the application of the various forces because of forces which tend to retard the missile even before it leaves the thrower’s hand, i.e. gravity (which tends to reduce upward motion) and the friction between the athlete and the ground at the instant of foot contact (which tends to slow the missile horizontally). The vertical forces in particular should be applied as simultaneously as practicable.

Turns, glides and run-ups should be as fast as an athlete can use to good purpose; never so fast that he is unable to exert full body force subsequently in the delivery. In this respect, each athlete possesses his own ‘critical’, optimum speed of preliminary movement.

For maximum speed of release the ground must provide adequate resistance to the thrower’s movements, and for as long as he is in contact with the missile, for the force he can exert against it is limited, very largely, by the counter-thrust of the ground.

Force in a horizontal plane can be lost when both feet are off the ground. As the athlete on the turntable attempts to put the shot, upper and lower parts of his body rotate in opposite directions ; reaction to his movement in a horizontal plane must be absorbed by the turntable and his body, not by the ground. Likewise, force applied vertically in throwing is also dependent upon the resistance of the ground.

As Housden points out, in developing angular momentum in discus throwing the athlete must have some part of each foot or, at least the whole of one foot, in contact with the ground. He recommends the following experiments; first, stand with both feet on the ground and with the right arm back behind the shoulder, swing the arm horizontally, and as it comes to the front of the body, raise the right foot and rise on the left toe. Through a transference of angular momentum from the arm, the body will then turn in the same direction. Then stand with the left foot flat on the ground and repeat the arm movement. There is again a transference of angular momentum. (Here, in both cases, the ball and heel of the foot exert equal and opposite horizontally-directed forces against the ground, which then exerts equal and opposite reactions, forming a couple.)

In a third experiment, stand with only the ball of the left foot in contact with the ground and repeat the arm movement. There will be no transference; (indeed, if the foot rests on a smooth surface, it will rotate towards the arm, in reaction, together with other parts of the body). From this, Housden concludes that a discus thrower is unable to increase his angular momentum from the moment his right foot leaves the ground in the back of the circle until the instant his left foot lands in the front of the circle, and both feet are on the ground again.

Certainly, a thrower can exert his greatest forces when both feet are firmly in contact with the ground. In the shot and javelin events in particular, however, effective contact by the rear leg is broken once it has completed its drive, and contact with the ground is maintained only by the leading foot . It is impor- ry> potation tant to consider the timing of the breaking of this rear leg contact in relation to the movement of the arm, to see how continued maximum horizontal force can be applied to the missile.

Taking shot putting as an example; when the front foot comes to the ground it loses speed. The horizontal force exerted by the ground has then a two-fold effect: it causes both athlete and shot to rotate about this foot, and reduces the forward speed of the Centre of Gravity common to athlete and shot.

This sudden checking force causes an instantaneous change in speed at each point of the putter’s body except one—below which all parts are slowed down, while all parts above this point are speeded up. It is important to realise that when the hand exerts a force on the missile, either above or below this special point, the reaction tends to move the feet forwards or backwards respectively. (When considering the movement of a rigid body, this point is known as the centre of percussion, and its exact position can be calculated. As our shot putter is far from rigid, however, it can only be said that this point will be some distance above the Centre of Gravity.)

By way of illustrating this principle; when a man holds a shot with both hands at arms’ length above his head and, after an upward jump, pushes the shot forward while he is off the ground, his feet should move forward ; but when, under similar circumstances, he thrusts the shot forward at chest height, the reaction should then move them backwards. (By the same token, when the arm circling is executed at the level of the man’s centre of percussion, his feet are unaffected and the movement invokes only the simplest of turntable reactions.)

In shot putting, correct technique requires the rear foot to be firmly in contact with the ground until the arm strikes , permitting the ground to resist the tendency of the feet to move backwards. Once this rear leg has done its work and the arm strikes higher, however, the backward reaction on the hand tends to move the front foot forward and the ground reacts against it, allowing continued maximum force to be exerted.

Throwers who break contact with the ground before the missile leaves the hand may do so for lack of arm and shoulder strength; for a combination of the implement’s inertia and accelerations developed by the legs and trunk may be too much for the arm—whose final action may have to be delayed until the accelerations have been reduced.

Or, again, contact could be broken prematurely to reduce the athlete’s forward motion. Or the feet may be too close together or otherwise incorrectly positioned. Or the arm could be striking too horizontally.

Maximum release speed in throwing (particularly in the shot, discus and javelin events) is influenced by the ‘hinged momenC principle , whereby, on attaining maximum, controlled (i.e. ‘critical’ speed at the end of the preliminary run-up, glide or turns, the front foot is checked.

As we have seen, the checking force at the foot is one of two equal parallel forces acting in opposite directions, producing a turning couple —a forward rotation, a ‘hinged moment’. This checking force also reduces the forward speed of the Centre of Gravity common to thrower and missile.

As the speed of a point on a turning body is directly proportional to its distance from the axis (which, in this case, is the athlete’s front foot) the throwing shoulder will now possess more speed than the Centre of Gravity, but whether or not it is greater than the thrower’s original linear speed depends upon the extent to which the Centre of Gravity slowed down. This, in turn, depends primarly upon the horizontal distance between the Centre of Gravity and the front foot as the latter comes to rest.

In javelin throwing, where this foot is far in advance of the Centre of Gravity , most—if not all—parts of the athlete lose speed at this instant. In so far as there is rotation about the foot, all parts of his body above the Centre of Gravity may move faster but not as fast, perhaps, as his linear speed immediately beforehand.

Such a sacrifice is still worth while to the javelin thrower, however; indeed, it has to be made in good throwing. The front foot must be stretched well ahead of the body in order to provide an effective throwing position and, in view of the thrower’s forward speed, to give sufficient time for the movements of throwing. The writer has seen no mathematical evidence to show that a javelin thrower’s upper body improves its linear speed as a result of the front foot coming to the ground, but if that speed is retained, or only slightly reduced, while the athlete adds his powerful throwing movements, it is obviously of great advantage, subsequently, to the speed of delivery.

In the shot and discus events, however, where (in comparison with the javelin thrower) at this instant the front foot is not excessively in advance of the Centre of Gravity (and where, therefore, there is less checking of forward speed), it seems very likely that there is a point which corresponds to a centre of percussion, with parts of the body above it speeded up; but this point will be changing constantly with changes in body position. (When the base of a rod (i.e. a thin, rigid, uniform rectilinear mass), moving horizontally in a vertical position, is brought to rest the speed of its Centre of Gravity drops by a quarter. If B is twice as far from A as the Centre of Gravity, it will move twice as fast as the Centre of Gravity; so the speed of B is improved by 50 per cent at the instant of checking. The centre of percussion in such a mass is always two-thirds AB from A. In a rigid non-uniform mass, however, the problem is very much more difficult.)

In throwing, the force exerted is to some extent dependent upon the athlete’s mass. In discus throwing, for example, as the arm strikes the tendency is for the rest of the athlete’s body (especially the throwing shoulder) to move downward and backward in reaction, so reducing the effective force and time/range over which force can be applied.

In good throwing, the reaction to the vertical component of the arm’s movement will be counteracted by the up-thrust of the ground, regardless of the thrower’s weight; but the reaction to the horizontal component will cause the upper-body of a comparatively light athlete to move backward more than a heavier thrower, other things being equal. The heavier man can therefore exert more effective force over greater distance.

It follows that an athlete who breaks contact with the ground prematurely in shot putting will in all probability find the error more costly than when throwing a discus since, obviously, the reduction in delivery impulse involves the ratio of missile weight to body weight, i.e. the mass of the missile times its speed, equals the athlete’s mass times his speed in an opposite direction. For this reason it has been argued that the reduction in delivery impulse owing to breaking ground contact before the discus leaves the hand is little more quantitatively significant than a gun’s recoil as a shell is launched.

Sheer mass is also of value in increasing the radius of movement in discus and (particularly) hammer throwing, increasing the missile’s speed. Since the axis of the thrower’s turning movement passes through his feet and the Centre of Gravity (common to athlete and missile) , a heavier athlete brings his shoulders closer to this axis than a lighter thrower.

Angle of release

If a thrower is to obtain maximum distance, it will not be sufficient to give the missile maximum release speed; it must also be thrown at an appropriate angle.

When points of release and landing are the same height above the ground (and aerodynamic factors may be ignored) the optimum angle for the projectile of a missile, regardless of its speed, is one of 45 deg.. In this case, vertical and horizontal component velocities are equal, and the missile also lands at a 45 deg. angle. (Here, distance is as the square of the velocity; so, for example, if the velocity increases by 10 per cent (from, say, 100 to 110 units) the distance will be increased by 21 per cent (from 100 to 121 units).)

It should be noted that the weight of a missile reduces the resultant vertically upward thrust delivered to it. To release, e.g. a shot at this angle, therefore, a thrower must exert a force vertically greater by 16 Ib-wt than the horizontal force.

However, in all four throwing events in field athletics the implement is thrown from a point above the ground and this affects the release angle. Then the optimum angle depends upon height and velocity of projection. In the shot and hammer events (where aerodynamic factors are of no account) the optimum release angle will be less than 45 deg. Theoretically, a missile thrown at this angle will land at an angle with the horizontal equal to the angle its release direction makes with the vertical. For example, a shot released at 41 deg. 40 min. will land at 48 deg. 20 min. (released 7 ft above the ground, at a velocity of 41-3 f.p.s. for a distance of 60 ft measured horizontally from the point of release).

The optimum angles of projection for a put of 60 ft (measured horizontally from the point of release to the point of landing, i.e. not allowing for the distance between the inside edge of the stop-board and the hand (approximately 1 ft)), from release heights of 8 ft, 7 ft and 6 ft, will be 41 deg. 12 min., 41 deg. 40 min. and 41 deg. 54 min. respectively. In hammer throwing the missile is released so close to the ground relative to the distance thrown that, for all practical purposes, 45 deg. can be assumed the proper angle of delivery.

The forces exerted in throwing give greater release speed when they are directed nearer to the horizontal. In fact, a study of the dynamics of shot putting reveals that within certain limits speed of release is more important to an athlete than the use of an optimum angle.

In theory, a shot projected 60 ft from a point 7 ft above the ground must rise to a height of 18 ft 9 in.. Yet most 60 ft shot putters do not put so high and therefore do not release the shot at such optimum angles. It could be said, of course that by contriving to improve their elevation they could put even farther—and this could well be true of some. It seems likely, however, that at such levels of performance the factors responsible for maximum release speed conflict with those that give an optimum angle of delivery. (i) 40 deg. is nearer the average optimum angle than 45 deg; (ii) from 35 deg. upward comparatively little increase is made in putting, for the same velocity; (iii) an increase in height of release from 6 ½ ft to 7 ft gives only an additional 5 to 8 in. in distance; from 7 ft to 8 ft only 9 to 15 in.; (iv) relative increases in velocity very decidedly increase distance. For example, putting from a height of 7 ft, at an angle of 35 deg. at 42 f.p.s., an athlete attains 60 ft 4 in., but gains only 1 ft 4 in. by increasing his angle by 5 deg.; whereas, by returning to an angle of 35 deg. and increasing his speed by only 1 f.p.s. he gains 2 ft 7 in., and as much as 5 ft 2in. for an increase of 2 f.p.s.

The proper use of the strong leg and trunk muscles in throwing plays a vital part not only in releasing the missile at maximum speed, but also in projecting it at a correct angle; in particular, where the angle is too low, leg and trunk action—and not the arm or arms—is almost entirely at fault.

In fact, the emphasis on ‘lifting’ the missile with the legs and trunk during the actual throwing movements should be considerable, especially where comparatively great horizontal speed has first been developed in the run-up or movement across the circle; for the angle of projection will be the product of the preliminary and throwing movements.

Aerodynamic factors

In discus and javelin throwing, distance depends upon the speed and angle of release, as with the shot and hammer events, but by virtue of their size and shape, aerodynamic forces also influence the flight of discoi and javelins. These missiles do not describe simple parabolic curves.

As yet, the aerodynamics of discus and javelin throwing have not been worked out in detail, for many unknown factors and variables (not the least variable of which is the thrower himself!) are involved. What follows is therefore no more than an outline of basic, relevant aerodynamic principles, with some comment as to their significance in these events.

General principles. In moving through the air a discus or javelin drives part of that air to the side and pushes some in front of it. This requires work and, therefore, a reduction in kinetic energy and, therefore, speed. The air’s resistance depends upon the shape and size of the missile; generally, the thinner and sharper it is at the front, the smaller is the resistance—which can be further reduced if its cross-section narrows gradually towards the rear, giving a ‘streamlined’ effect.

In front of the missile, therefore, there is a region of increased air pressure, and in its path another region where the air whirls irregularly, causing diminished pressure. The kinetic energy of turbulent air movement in the wake of a discus or javelin accounts for much of the work needed to move it through the air; but the better the stream- lining, the smaller will be this air disturbance. present the same effective cross-section to the on-coming air yet, because of its streamlining, object b has 1/25 the specific resistance of a.)

Air resistance is also dependent upon the speed of the discus or javelin, and is proportional to the square of the velocity.

When a missile is inclined at an angle to the wind the resultant of the forces exerted upon it by the air can then be resolved into vertical (lift) and horizontal (drag) components. The ratio between lift and drag depends upon the angle of attack, i.e. the acute angle between the plane of the discus or javelin and the direction of the relative wind. Even small variations of this angle can sometimes produce abrupt alterations in the lift/drag ratio.

The term relative wind refers to the movement of the air in relation to the missile. All motion is relative; a discus or javelin can be suspended in an air-tunnel with the air flowing past, or it can be moving through still air. A following wind can therefore reduce the speed of the relative wind (lessening lift and drag) and a headwind can increase it (but must not be too strong to be of benefit in these two events).

A relative wind will not always directly oppose the flight-path of the missile’s Centre of Gravity, however; usually, in throwing, air currents are continuously varying in both strength and direction. Nor, always, do the missile’s flight-path and its plane coincide, an angle between being called the angle of incidence; this can be positive (i.e. above the angle of the flight path) or negative (i.e. below that angle). The angle between the plane of the missile and the horizontal is called the attitude angle.

The sizes of the various lifting forces acting on a discus are dependent upon the angle of attack. When the angle is zero the upward forces on the lower surface act only near its leading edge; but as the angle increases these forces also increase, both above and below the discus. When the angle is of a certain size, however, air turbulence forms along the trailing edge and grows markedly with a further increase in angle.

The shape of the discus or javelin and the angle it makes with the direction of the relative wind cause the speed of the air flowing over the missile’s upper surface to be greater than that underneath. As a result, there is a diminished air pressure above the missile and the upward forces acting on it are greater than the downward forces.

All the forces of the air acting on a discus or javelin may be added together to form a resultant which acts at a point called the centre of pressure. This changes position with a change in the angle of attack; as this angle increases, the centre of pressure moves forward and the resultant force increases. Conversely, with an increase in the speed of the relative wind, the centre of pressure moves farther back. There is a limit to which the angle of attack can be increased to advantage, and if that limit is exceeded turbulence behind the missile disturbs the smooth flow of air over its upper surface; the upward force (lift) almost disappears, drag increases and the missile stalls. This limiting angle is called the stalling angle.

The lifting force acting on a discus or javelin in flight therefore depends upon: (i) its shape (which influences the nature of the air-flow past its upper and lower surfaces); (ii) the angle of attack (within limits, the greater angle produces the greater lift); (iii) the surface area (the greater the area, the bigger the total lifting force); (iv) the square of the air speed (for example, lift is four times greater when a javelin is released at 50 m.p.h. than at 25 m.p.h.); (v) air density (the greater the density, the greater the lift).

The flight of the discus. A discus (which experts think a comparatively poor aerodynamic design) ‘performs most efficiently as an airfoil between speeds of 69-8 and 80 feet per second’ (Ganslen), and its spin, in good throwing, provides some gyroscopic stability in flight, keeping the lift/drag ratio relatively constant.

For all its gyroscopic benefit, however, spin itself tends to increase the angle of attack (Housdenf)—a paradox which, perhaps again, shows how, in the analysis of ath letic movement, advantages must be weighed against disadvantages.

To illustrate: when a discus rotates in a clockwise direction its left side meets pressure the air at a greater speed than its right side; the former spins into the air, while the latter moves away from it. Therefore the upward force exerted by the air on the left side is greater and the centre of pressure is to the left. There is therefore a tendency for the discus to turn about the axis XOX1 (clockwise, as seen from X).

This does not happen, however, because of its spin. Assuming an upward pressure exerted somewhere on OY , this turns the discus about the axis OY (clockwise, as seen from Y); for each point on the missile is raised as it moves across OX and continues to rise until it reaches OX1 ; every point on the discus is higher at X1 than at X and, as a result, its front edge tilts upwards. Conversely, a downward force exerted at the centre of pressure will lower this front edge.

The following figures show estimated distances a discus can be thrown for given initial speeds, using combinations of projection and attitude angles (Cooper, Dalzell and Silverman (Purdue University) from wind-tunnel data supplied by Ganslen). Here it has been assumed that spin stabilises a discus, in good throwing, to the point of maintaining a constant attitude angle (the authors claiming that motion picture analysis indicates no appreciable change in this angle throughout flight).

The following conclusions may be drawn from these tables. (1) Speed of release is the factor of greatest importance, as emphasised previously. A small increase in speed in discus throwing gives a comparatively larger increase in distance, however, because the lift on the missile is proportional to the square of its speed. (2) For a given speed, the most important variable is the angle of projection. 150 to 200 ft throwers should project at 35 deg. to 40 deg.; throwers of lesser ability should increase the angle slightly, but never above 45 deg. (3) The attitude angle should be between deg. and deg. At the instant of release, therefore, there should be a negative angle of incidence of approximately 5 deg. to 10 deg. Although, at such an angle, air pressure will tend to depress the front edge of the discus, the ascending half of its flight-path automatically reduces the angle. If the latter tendency is the greater, then the missile moves gradually into alignment with the tangent to the path of its Centre of Gravity— presenting a considerable surface-area to the ground during the descending half of the flight, benefiting by the cushioning effect of the air beneath and, therefore, gaining distance through a gliding motion.

On the other hand, a positive angle of incidence upon release must increase as the discus moves forward and its flight-path curves towards the ground. In addition, air pressure increases this angle, leading to a progressively stronger resistance to forward motion and, eventually, stalling. (The stalling angle for a discus is said to be approximately 30 deg. (Ganslen).)

The greater the speed of the discus upon release, and the stronger the opposing wind, the smaller should be the attitude angle as the discus leaves the hand, to avail the throw of a more favourable lift/drag ratio. Practical experience proves that a discus can be thrown farthest into a wind blowing from front-right , and Pharaoht (Great Britain; 4th, Discus, 1956 Olympic Games) has maintained that the difference between throwing directly into a wind, and with that same wind, varied—for him—from about 5 ft for a wind-speed of 7 m.p.h. to approximately 15 ft at 20 m.p.h., the greater distance being thrown into the wind. Stronger headwinds reduce stability in flight and therefore shorten the distance.

Flight of the javelin. From 1955 to 1961 javelin throwing world records rose primarily through the use of implements of improved aerodynamic design, giving an increased stability and a better lift/drag ratio in flight. They were considered to add as much as 25 ft to a good throw. These ‘glider’ javelins, as they came to be called, were made in several different diameters to suit a thrower’s ability and varying throwing conditions; they possessed a lighter spearhead, a more evenly-distributed surface-area and tapered less towards the tail than previously.

The year 1961 saw the end of this era of javelin throwing, however, because the International Amateur Athletic Federation further revised its specifications so as to limit these aerodynamic features and enforce a stricter uniformity as to the type of javelin used throughout the world. The javelin now permitted has a reduced diameter (a maximum of 30 mm as against the previous 35 mm) and its angle of taper and length of point are also specified. However, the regulations still permit some variation, for the javelin-diameter can vary from 25 mm to 30 mm and its Centre of Gravity can be between 90 cm and 110 cm from the point. Compared with the javelins used prior to 1955, in fact, the present implement remains ‘aerodynamic’.

There is considerable disagreement and ignorance, even among experts, as to the behaviour of an aerodynamic javelin in flight, and little reliable scientific information on this subject at the present time.

A Russian opinion, that of V. L. Kuznetsov, assesses the optimum angle of release for the modern javelin at 28 deg. to 30 deg., ideally with the shaft at this instant in alignment with the tangent to the path of its Centre of Gravity (i.e. with a zero angle of incidence). Certainly, when this improved javelin is released at much greater angles (e.g. at approximately 45 deg., as necessary in throwing the ‘old’ design) the tendency is to give it too great an angle of attack. It then rises and falls abruptly, for its centre of pressure is too far in front of its Centre of Gravity, creating backward rotation and stalling. (These two centres and the distance between them then create a couple whose turning effect is proportional to that distance (i.e. the arm of the couple).)

Some experts are of the opinion that the optimum release-angle of these aerodynamic javelins is nearer 40 deg., with an angle of incidence at this instant of approximately -10 deg.; but they admit that an athlete must be very skilful to use it without creating too great an angle of attack, for in attempting to produce more ‘lift’ in the delivery, the tendency is to raise the head of the javelin. It is easier to control this angle when the delivery is more horizontal, and most athletes prefer to ‘play safe’ in this way.

In an aerodynamically well-designed object the centre of pressure remains comparatively stable in flight; the relatively even distribution of surface-area of the modern javelin is said to reduce the motion of its centre of pressure as it travels through the air. However, even in good throwing it seems certain that this point changes position to some extent—initially, perhaps, acting a little in front of the Centre of Gravity, before moving back during the flight to bring about a slight contrary rotation for landing at a shallow angle.

Rotation of the javelin (in this sagittal plane) is also influenced by the position of the thrower’s grip in relation to the missile’s Centre of Gravity—the point about which rotation must take place in the air. The farther behind this point the grip is (particularly the hand’s last contact with the javelin) the greater will be the tendency for the spearhead to drop prematurely; for the thrower’s upward component of force, and gravity acting through the javelin’s Centre of Gravity, then create a couple.

On the other hand, the closer the grip is to the Centre of Gravity, the smaller will be the rotational effect and the easier it will be for the athlete to exert his final force of delivery correctly. In general, good throwers prefer the Centre of Gravity to be as far away from the spearhead as the rules permit, with their grip as close as possible to the Centre of Gravity.

In the process of releasing a javelin a thrower automatically imparts spin about its long axis—the result of an outward rotation of his elbow and the sequence with which his fingers break contact during delivery. This spin (clockwise, seen from behind, in the case of a right-handed thrower) can possibly give some gyroscopic stability in flight, provided it is of sufficient intensity. However, whereas some experts speak in terms of thirty revolutions per second in a good throw, and regard this spin as important, others deny that much spin is ever developed or has any significance. To summarise: (1) Again, speed of release is the factor of greatest importance as in all other throwing events, and lift on the javelin is proportional to the square of its speed. Within limits, thinner javelins can be selected and used to reduce the drag factor. (2) The optimum angle of release for the ‘aerodynamic’’’ javelins is probably between 35 and 40 deg.; the ‘old’ design of javelin should be released at approximately 45 deg. (3) The attitude angle of the ‘aerodynamic’ javelin at release should possibly be a little less than the release angle; the vital thing, here is not to present too great an angle of attack to the relative wind. Then, in a good throw, the missile will reduce its angle to the horizontal slightly and maintain that angle until it begins to fall, when it again rotates forward to land almost flat, point first. (4) The gliding qualities of the ‘aerodynamic’ javelin are especially valuable in the gaining of distance during the second half of flight.

Throwing techniques

Hammer. Technique, in good hammer throwing , is designed to release the missile at the greatest possible speed at an optimum angle of approximately 45 deg. from a circle 7 ft in diameter, so that it lands within the prescribed throwing area.

Hammer speed and a rotational pattern are established during (usually two) preliminary swings before the hammer’s speed is markedly increased and its plane of motion is steepened progressively during (usually three) turns

The system of man and hammer rotates about an axis passing through their common Centre of Gravity and the thrower’s contact with the ground. The good thrower works his way across the circle diameter by pivoting alternately on the heel and ball of his left foot. Thus, in the course of making these turns, he moves the common axis from the rear to the front of the circle. Finally, he imparts even greater speed to the hammer-head by lifting it powerfully with his legs and trunk.

As, in any rotation, a hammer’s linear speed will be directly proportional to its distance from the common axis , in good throwing relaxed arms are used merely as a prolongation of the wire shaft, fully extended in the turns and final delivery— pulled out by centrifugal force.

From Newton’s First Law it follows that the hammer would move in a straight path but for the force of gravity and a centripetal (i.e. pulling-in) force exerted by the athlete—a force proportional to the square of the missile’s linear speed. If, for example, the hammer’s speed is doubled, the thrower must then exert four times the centripetal force, automatically increasing an equal but opposite centrifugal (i.e. pulling-out) force.

From turn to turn, therefore , the thrower experiences increased difficulty in maintaining balance and control; for, in a sagittal plane, the hammer’s centrifugal pull and the equal but opposite force from the ground thrusting against his feet tend more and more to rotate him forward.

Because the thrower’s balance in this plane is the product of two pairs of equal forces acting in opposite directions , to counteract this tendency the skilled hammer thrower ‘sits’ in progressively deeper positions from one turn to another, thus increasing the horizontal distance between the force of his weight (acting vertically downwards) and the equal but opposite force passing vertically upwards through his feet. By lowering the Centre of Gravity, this ‘sitting’ also progressively improves the thrower’s stability.

The athlete accelerates the hammer by exerting horizontal and vertical components of force. (1) Horizontally, he is able to apply force only because of the friction between his feet and the ground—through the reactions of the ground to the forces exerted by his feet. This friction also enables the thrower to accelerate the hammer in this plane by movement of the common axis; (e.g. the rotational acceleration of a conker on a string in this plane is possible by virtue of moving such an axis ).

The speed of the hammer-head can be increased horizontally as a result of the thrower’s exerting a centripetal force; as, in good throwing, the arms are extended throughout, such a force can be applied only by moving the common axis. In fact, its movement across the circle is essential to imparting the greatest possible centripetal impulse to the hammer-head, and to this end the weight of the thrower must be maintained over his pivoting leg throughout (for if this axis falls between the feet or over the trailing foot, progression across the circle is impaired).

Tangential acceleration is further improved when the thrower leads the hammer-head. Here he obtains ‘body torque’ through leading markedly with his hips and legs, moving his feet ‘fast and early’ (Cullum) in the turns. In such a case, the apparent radius of hammer movement (i.e. a straight line from the thrower’s left shoulder to the hammer-head) is at an angle to the true radius (i.e. the distance between the hammer-head and the common Centre of Gravity). In fact, whenever the wire shaft is not at right angles to the curve along which the hammer-head is moving, the hammer will be acclerating and, correctly, the thrower will be ‘maintaining contact’ through his left arm (Cullum). (Note the reference to ‘leading’ the hammer-head here, as opposed to ‘trailing’ it. The latter, to a hammer thrower, indicates a bending of the right arm with a resulting shortening of hammer radius; whereas, to ‘lead’ the hammer indicates a trunk twist —infinitely preferable).

To re-emphasise: such methods of accelerating the hammer horizontally are possible only by virtue of the friction between the thrower’s feet and the ground, and this can attain its greatest value when both feet are in contact with the ground and the hammer-head is below the level of the shoulders. (Maximum friction, here, depends on the pressure between the feet and the ground ).

This is particularly true of acceleration through ‘body torque’. Friction will be increased when the common axis leans away from the missile. In that phase of a turn where the thrower pivots on one foot , and with only its outside edge touching the ground, horizontal acceleration can therefore be only very small if, indeed, it is at all possible; for in such a position pressure between foot and ground has a minimum value. (2) Vertically, the hammer can be accelerated upwards and downwards during each successive 360 deg. turn, and in good throwing this vertical acceleration increases progressively from turn to turn— and is of vital importance to the delivery. (i) Vertically upwards. The hammer can be accelerated upwards as soon as the hammer-wire is inclined upwards to the vertical, and this acceleration would appear to attain its maximum value shortly after the hammer-head has passed its lowest point, i.e. off the right foot ). Here, the force applied to the hammer-head is limited by that which the athlete can exert downwards through his feet (preferably both feet simultaneously) against the ground. Therefore, given the position from which to apply such a force, the limiting factor is the strength and speed of the athlete.

The direction of the reaction obtained from the ground will be upward with the hammer at its lowest point and will diminish gradually and change more to the horizontal as the hammer-head rises. (ii) Vertically downward, acceleration is achieved by permitting the body weight to drop just before the hammer-head itself drops in its swings or turns. Here, therefore, the limiting factor to acceleration is the thrower’s weight—whch can be lowered with or without contact with the ground.

First turn Third turn

With a steepening of the plane of hammer movement and a progressive increase in its linear speed from turn to turn, vertical means of acceleration become increasingly important and horizontal means comparatively less so.

When the hammer-head is moving with sufficient speed through the higher ranges of its spiral course, the vertical component of the athlete’s centripetal force sometimes exceeds the weight of his body, and his feet are lifted off the ground as a result.

This is exemplified even in the throwing of world-class hammer throwers, whose feet sometimes leave the ground, momentarily, on their final turn to the detriment of the delivery position. In fact, throwers often jump round on this last turn because the speed of the hammer is too great for their ability to advance their hips and feet in any other way. However, by this means the hips are never so well advanced— relative to the shoulders and hammer-head—as in a suitably fast pivot on one foot; but for this, of course, the thrower needs tremendous speed and dexterity.

Discus. If a discus is to be thrown a maximum distance it must be released with the greatest possible speed at an optimum angle—the latter being influenced quite considerably by the aerodynamic factors discussed already.

In the sense that both are rotational in character, some similarity exists between this event and hammer throwing. Yet, otherwise, they have little in common. For whereas the hammer is slung from a wire which can only transmit force along the direction in which the wire lies, the discus is thrown from an arm, and whenever the thrower’s hand has a firm grasp on the implement there is little limitation to the direction in which that hand can exert force on the discus.

From a position at the rear of the 8 ft 2£in. (2£ m) circle, and with his back to the direction of throw, the athlete executes several (usually no more than three) preliminary swinging movements, using his entire body—not the arm alone. These movements help to prepare him emotionally for the throw and develop a movement pattern important to the efficiency of the turning and throwing movements which follow.

The thrower then shifts his weight over his left (pivoting) foot, turns and drives quickly across the circle. Here, it is important to use just the correct quantity of spin on this pivoting foot; novices often spin too far, to the detriment of their throwing position, subsequently. In driving across the circle it is also important to main- tain a correct relationship between this pivoting foot and the thrower’s Centre of Gravity; the faster the movement across, the farther forward of this foot should be the Centre of Gravity. Through failure to maintain this relationship novice throwers often lose balance falling backwards in the throw. (Ryan.)

In this phase the expert’s shoulders turn through approximately 450 deg. and, correctly, he develops maximum controlled angular and linear velocities. In the turn—part pivot, part jump, part running movement—the axis of movement passes through the common Centre of Gravity and his base—i.e. first his left foot and then the right. A relaxed throwing arm trails fairly wide of the body, encouraging maximum possible radius of movement in the throw which follows; for, for a given angular velocity, the linear speed of the discus will be proportional to its distance from the common axis.

The trailing of the throwing arm also increases the moment of inertia of the upper body relative to the common axis, tending to slow those parts of the body down in their rotation; simultaneously, by keeping the thighs close together in the turn (i.e. reducing their moment of inertia about this axis) the rotation of the lower parts is speeded up. Hence, body torque is built up and maintained. (However, some great throwers build up angular momentum in their hips and legs through a wide leg-sweep during the first half of the turn. When, subsequently, the free leg is pulled in, torque between hips and shoulders is increased—an affect enhanced by a deliberate effort to hold back the upper body by bending the free arm across the chest.)

The expert discus thrower also advances his hips and feet relative to his upper body by stressing the pick-up and rotational movement of his free leg as he drives from the rear of the circle, by getting his right foot to the ground again quickly and by positioning his front foot without delay. And this is achieved without raising his Centre of Gravity unduly, and with both feet off the ground for only an instant—otherwise, when the thrower lands in the front half of the circle, his upper body will have begun to catch up his hips, to the detriment of body torque and the power of his throwing position

The expert also lands on a flexed right leg and with his weight well over it. He then adds to the speed of the discus by trans- total distance in a 60 ft put. Certainly, the glide ought never to be executed to the detriment of power of position and control in the delivery, subsequently; i.e. it should never take up too much of the circle, so cramping the putter’s delivery; or be too fast, to the point of exceeding his ‘critical’ speed.

It can be seen that Rowe’s glide took him rather less than half-way across the circle, permitting a breadth of base suited to his height, horizontal speed and lean over his rear leg.

The actual putting action must begin immediately the athlete’s rear foot comes to rest at the end of the glide, otherwise valuable time will elapse without acceleration being given to the shot. As soon as this rear foot lands, its leg can exert an efficient upward thrust and the trunk and shot can be raised.

However, since maximum body force and maximum rotation of the trunk about its long axis are possible only with the other foot used as tain a correct relationship between this pivoting foot and the thrower’s Centre of Gravity; the faster the movement across, the farther forward of this foot should be the Centre of Gravity. Through failure to maintain this relationship novice throwers often lose balance falling backwards in the throw. (Ryan.)

In this phase the expert’s shoulders turn through approximately 450 deg. and, correctly, he develops maximum controlled angular and linear velocities. In the turn—part pivot, part jump, part running movement—the axis of movement passes through the common Centre of Gravity and his base—i.e. first his left foot and then the right. A relaxed throwing arm trails fairly wide of the body, encouraging maximum possible radius of movement in the throw which follows; for, for a given angular velocity, the linear speed of the discus will be proportional to its distance from the common axis.

The trailing of the throwing arm also increases the moment of inertia of the upper body relative to the common axis, tending to slow those parts of the body down in their rotation; simultaneously, by keeping the thighs close together in the turn (i.e. reducing their moment of inertia about this axis) the rotation of the lower parts is speeded up. Hence, body torque is built up and maintained. (However, some great throwers build up angular momentum in their hips and legs through a wide leg-sweep during the first half of the turn. When, subsequently, the free leg is pulled in, torque between hips and shoulders is increased—an affect enhanced by a deliberate effort to hold back the upper body by bending the free arm across the chest.)

The expert discus thrower also advances his hips and feet relative to his upper body by stressing the pick-up and rotational movement of his free leg as he drives from the rear of the circle, by getting his right foot to the ground again quickly and by positioning his front foot without delay. And this is achieved without raising his Centre of Gravity unduly, and with both feet off the ground for only an instant—otherwise, when the thrower lands in the front half of the circle, his upper body will have begun to catch up his hips, to the detriment of body torque and the power of his throwing position

The expert also lands on a flexed right leg and with his weight well over it. He then adds to the speed of the discus by trans- ferring that weight from rear to front foot, thus shifting the common axis; simultaneously, he stretches and lifts powerfully with legs and trunk and unwinds his upper body and throwing arm through approximately 180 deg. of additional shoulder rotation. All this takes place against a bracing and lifting action of his left leg, the foot of which is placed only slightly to the side of his general line of direction across the circle this foot remains in contact with the ground until the discus has left the hand.

After the left foot meets the ground and the actual throwing movement begins the path of the discus describes a spiral curve, first descending and then rising steeply, but inclining more to the horizontal as the point of release (just in front of the line of the shoulders) is approached. Early in its rise the hand has a firm grasp and during this period can exert a vertical or near-vertical force on the implement. In fact, the lifting of the trunk and legs must take place at this time, while the hand can transmit vertical force.

Later, the upper edge of the discus drops away from the wrist and any force applied through the fingers must then pass through the Centre of Gravity of the implement—otherwise it will wobble, to the detriment of its stability in flight. Consequently, a series of velocities is given to the discus at this stage, beginning vertically but tending towards the horizontal. A combination of these velocities results in the discus starting its flight with a negative angle of incidence.

Shot. The technique of shot putting is simpler than that of each of the other three throwing events, lending itself easily to mechanical analysis through the use of cine film.

By taking cine pictures from a fixed camera set on a continuation of the line dividing the circle into front and rear halves, preferably against accurately-positioned background markings, and focussed on a point approximately 3 ft directly above the middle of the circle, these pictures can be projected, subsequently, frame by frame or at other regular intervals of time, and the path of the shot can be plotted.

Then, provided the camera speed is known, it is possible to calculate the (a) time taken for the put, (b) acceleration of the shot in a sagittal plane, from stage to stage, (c) its path across the circle in this plane, (d) release speed, (e) height of the point of release, (f) and angle of projection; and from (d) (e) and (f) compute (g), the distance of the put.

The purpose of the glide is primarily to give the athlete and the shot horizontal speed prior to the delivery in the front half of the circle. The glide is important, yet not too much importance should be attached to it, as it accounts for only about 7 per cent of the total distance in a 60 ft put. Certainly, the glide ought never to be executed to the detriment of power of position and control in the delivery, subsequently; i.e. it should never take up too much of the circle, so cramping the putter’s delivery; or be too fast, to the point of exceeding his ‘critical’ speed.

It can be seen that Rowe’s glide took him rather less than half-way across the circle, permitting a breadth of base suited to his height, horizontal speed and lean over his rear leg.

The actual putting action must begin immediately the athlete’s rear foot comes to rest at the end of the glide, otherwise valuable time will elapse without acceleration being given to the shot. As soon as this rear foot lands, its leg can exert an efficient upward thrust and the trunk and shot can be raised.

However, since maximum body force and maximum rotation of the trunk about its long axis are possible only with the other foot used as a point of resistance, the front foot should land only fractionally after the rear foot; here, there should be just sufficient rocking motion from one foot to the other to help keep the common Centre of Gravity moving forward. A slight rock will, in fact, help bring the front foot to the ground; on the other hand, with too much weight over the back leg at this stage, and with the front foot poised long in the air, the athlete will lose much, if not all, the speed built up during the glide.

Contrary to the view that the putting action ‘is a movement which begins in the toes and ends in the fingers’, in fact movement begins in the stronger but slower muscles surrounding the athlete’s Centre of Gravity and is then taken up, below the hips, at the knees, ankles and feet, in that order; simultaneously, above the hips, it extends upwards through the putting shoulder, elbow, wrist and fingers. In its summation of forces , therefore, a technically sound putting action can be likened to the throwing of a stone into a pool of water—causing the ripples to flow outward.

Theoretically, there can be no doubt that, throughout the putting movements in the front of the circle, the front foot should be firmly in contact with the ground, providing the necessary resistance for the hand to exert maximum force both vertically and horizontally. The vertical component of force must exceed the force of gravity to ensure continuous, though varying, upward acceleration. Horizontally, as soon as the hand rises above the centre of percussion the backward thrust of the shot on the hand encourages the front foot to move forward.

However, it must be admitted that a majority—if not all—of the world’s 60 ft shot putters do in fact break contact with this front foot fractionally before the missile leaves the hand. This may be to avoid moving beyond the stop-board; for by this means, the athlete reduces some of his forward momentum. Or, the legs may be driving too vertically (possibly because the feet are too close together) or the arm striking too horizontally. Again, this could happen because of the accelerations developed by the legs and trunk—accelerations which may be too great for the strength of the arm; arm action may have to be delayed until these have been reduced, if not completed.

Javelin. The ideal, in this event, is to combine maximum controlled approach-speed with a throwing position which enables maximum force to be applied to the javelin over the greatest possible range , releasing it at an optimum angle. g h I

Throwers are rarely satisfied with their combining of these two largely irreconcilable factors; yet, always, their aim is to obtain an effective throwing position with the javelin already moving fast—and then, with the throwing shoulder travelling at maximum speed relative to the ground, to impart maximum hand speed in relation to the shoulder.

For the greater part of his 14-17 stride (overall) run-up the expert thrower holds the javelin over his shoulder in a position which permits relaxed, balanced running, and accelerates gradually into a horizontal speed governed by his ability to exert full body force, subsequently, in his throwing movements. Approach speed should depend upon body speed and strength.

After 10-12 of these running strides he withdraws and aligns the javelin in preparation for the throw, turning and gradually leaning his trunk to the rear to adopt a powerful pulling position. The change in the angle of the trunk is particularly marked during the so-called ‘cross-step’ immediately prior to the throwing stride , where it is essential that the thrower contacts the ground with his right foot before his body weight moves over and beyond this foot.

Here, in a good throw, the athlete’s grip will be approximately 4 ft behind his Centre of Gravity which, in turn, will be to the rear of his right foot. The line of the leading leg and trunk at this instant will be about 30 deg. to the vertical, but the angle should depend upon the speed of the run-up, the greater speed requiring a greater angle, and vice versa. The thrower coasts through this transition from running to throwing position, yet his strides quicken progressively.

Basically the javelin throwing action can be described as, first, a powerful pull exerted on the missile, followed by a lifting motion, where ‘the thrower attempts to run off and away from the rear leg against the resistance of the frontleg’ (Pugh).

Beginning as the right foot con tacts the ground at the end of the cross-step and with the throwing arm comparatively straight and relaxed, a pull from the shoulder is applied as the weight of the body moves for ward and the front foot reaches out. And as this weight moves ahead of the sup porting foot, the right leg drives hard to add to this pulling movement and keep the right hip, in particular, moving fast into the throw. In good throwing, this transference of weight against the resistance of the front leg occurs without a premature turning of the shoulders to the front; in fact, the hips twist fractionally ahead of the shoulders.

So widespread are the feet in good javelin throwing that the rear leg completes its drive before the front foot contacts the ground. Trunk rotation occurs mainly by virtue of the front foot’s resistance to horizontal motion. A quick turning-in of the rear knee and foot adds to hip speed and coincides with an outward rotation and raising of the throwing elbow which arc essential to a final flail-like arm action.

The javelin and the athlete’s body are maintained in a single vertical plane, with all pulling forces exerted through the length of the implement.

If the trunk is too erect and the throwing base too narrow for the athlete’s approach speed, he will lack sufficient range over which to apply his body forces and will tend quickly to rotate in a sagittal plane over and beyond his front foot in delivery, pulling the javelin down. On the other hand, if he leans back too far and his feet are too widespread, the Centre of Gravity’s forward speed will be reduced excessively , the hips will not pass over the forward foot and, incorrectly, the trunk will pivot about the hips, shortening the radius of movement in a sagittal plane and, again, pulling the javelin down in delivery.

It is difficult to estimate the actual loss in forward speed of the Centre of Gravity due to the impact of the front foot with the ground, but even in a good throw it seems likely that this will be about one quarter of its original horizontal speed, depending upon the efficiency with which the front foot takes up the shock on impact. However, it may well be that the throwing shoulder at least maintains, if not increases, its linear speed, because of its distance above the Centre of Gravity. (M. J. Ellis and H. H. Lockwood agree that the speed of the throwing shoulder increases markedly as the front foot meets the ground, but suggest that this is due to the shoulder’s rapid rotation about the body’s longitudinal axis. In analysing film of one thrower they found that his Centre of Gravity did not describe an arc during the throwing stride, because of his flexed front leg, which kept the Centre of Gravity moving horizontally. They concluded that the hinged effect in this event occurs more in a horizontal than sagittal plane, commenting, ‘Perhaps, whilst the hinged moment effect (in a sagittal plane) is theoretically and mechanically ideal, the stresses that it would place on the thrower are such that the innate protective mechanisms of the body would not allow it to be used, even assuming that the thrower is strong enough to remain rigid.’)

Because, in good throwing, the athlete’s rear foot must break effective contact with the ground before the arm applies its forces, the arm’s first pulling movement, acting at shoulder-level below the point of percussion, must be exerted against the inertia of the thrower’s body, so reducing his forward speed. However, once the front foot meets the ground it remains in contact until the javelin is released, and so provides an essential resistance not only to any vertical component of the force of the arm action, but also to those horizontal components exerted, subsequently, above the point of percussion.

The final flail-like arm action of the good javelin thrower is brought about, first, by outwardly rotating the elbow and raising it higher than the hand grasping the javelin—’leaving that hand behind’ (Pughf)—before quickly extending the forearm and hand to apply further force vertically and through the javelin’s length.

This flailing arm action is superior to a straight-arm, bowling action, because: (i) the muscles acting between the forearm and upper arm, as well as the muscles acting between the shoulder and upper arm, can be used to produce force; (ii) the small moment of inertia of the comparatively light forearm and hand about the elbow joint does not hinder greater angular speed of the forearm relative to the elbow (although, of course, the moment of inertia of the javelin about this joint must also be considered); and (iii) In a straight-arm rotation about the shoulder, angular speed would have to be developed against the considerable moment of inertia of the whole arm and javelin.

Thus, the essential pulling character of a good javelin throw derives from (a) the motion of the body in front of the missile, (b) the body’s rotation in two planes—sagittal and horizontal, and (c) a final flail-like arm action. This pulling movement can take place over as much as 14 ft (Pugh)—from the moment the right foot lands at the end of the cross-step to the instant of release.

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