Acrobatic Diving at the Olympic Games - by Anne Shier (a.k.a. "Annie")

(From the web site:  http://en.wikipedia.org/wiki/Diving)

Diving is the sport of jumping or falling into water from a platform or springboard, sometimes while performing acrobatics. Diving is an internationally-recognized sport that is part of the Olympic Games. In addition, unstructured and non-competitive diving is a recreational pastime.

Diving is one of the most popular Olympic sports with spectators. Competitors possess many of the same characteristics as gymnasts and dancers, including strength, flexibility, as well as, kinesthetic judgment and air awareness. Kinesthetic judgment and air awareness may also be expressed as “proprioception”, which is a third distinct sensory modality (in the human brain) that provides feedback solely on the status of the body internally. It is the sense that indicates whether the body is moving with the required effort, as well as where the various parts of the body are located in relation to each other.

China came to prominence several decades ago when the sport was revolutionized by national coach Liang Boxi and after intense study of the dominant American, Greg Louganis. China has lost few world titles since. The success of Greg Louganis has led to American strength in diving internationally. Other noted countries in the sport include Italy, Australia and Canada.

Platform Diving:

A diving platform or diving tower is a type of structure used for competitive diving.

Indoor Diving Platform:

They consist of a vertical rigid "tower" with one or more horizontal platforms extending out over a deep pool of water. In platform diving, the diver jumps from a high stationary surface. The height of the platform(s) - 10 metre/33 feet, 7.5 metre/24.7 feet and 5 metre/16.5 feet - gives the diver enough time to perform the acrobatic movements of a particular dive. There are additional platforms set at 3 metres/9.84 feet and 1 metre/3.28 feet. These are primarily for practice and building confidence before moving a new diver to the higher levels. Diving platforms for FINA sanctioned meets must be at least 6 metres/19.8 feet long and 2 metres/6.6 feet wide. Most platforms are covered by some sort of matting or non-slip surface to prevent athletes from slipping.

All three levels of the platform are used in “JO” and NCAA competition. Each level offers a distinct degree of difficulty (DD) and therefore could yield different scores for divers.

Scoring the Dive:

Ultimately, the judges' scores given on each dive are subjective. However, there are specific rules governing how a dive is supposed to be scored. Usually a score factors three elements of the dive: the approach, the flight, and the entry. The primary factors affecting the scoring are: (1) the platform selected (10-meter, 7.5-meter, or 5-meter), (2) if a hand-stand is required and the length of time and quality of the hold, (3) the height of the diver at the apex of the dive, with extra height resulting in a higher score, (4) the distance of the diver from the diving apparatus throughout the dive (a diver must not be dangerously close, should not be too far away, but should ideally be within 2 feet (0.61 m) of the platform), (5) the properly defined body position of the diver according to the dive being performed, including pointed toes and feet touching at all times, (6) the proper amounts of rotation and revolution upon completion of the dive and entry into the water, and (7) angle of entry (a diver should enter the water straight, without any angle). Many judges award divers for the amount of splash created by the diver on entry, with less splash resulting in a higher score.

To reduce the subjectivity of scoring in major meets, panels of five or seven judges are assembled. In the case where five judges are assembled, the highest and lowest scores are tossed and the middle three are summed and multiplied by the DD. In the case where seven judges are assembled, the highest and lowest scores are tossed and the middle five are summed and multiplied by the DD. Accordingly, it is extremely difficult for one judge to manipulate scores.

There is a general misconception about scoring and judging. In serious meets, the absolute score is somewhat meaningless. It is the relative score, not the absolute score that wins meets. Accordingly, good judging implies consistent scoring across the dives. Specifically, if a judge consistently gives low scores for all divers, or consistently gives high scores for the same divers, the judging will yield fair relative results and will cause divers to place in the correct order. However, absolute scores have significance to the individual divers. Besides the obvious instances of setting records, absolute scores are also used for rankings and qualifications for higher level meets.

Competitive Strategy:

To win dive meets, divers create a dive list in advance of the meet. To win the meet the diver must accumulate more points than other divers. Usually simple dives with low DDs will look good to spectators but will not win meets. The competitive diver will attempt the highest DD dives possible with which they can achieve consistent, high scores. If divers are scoring 8 or 9 on most dives, it may be a sign of their extreme skill, or it may be a sign that their dive list is not competitive, and they may lose the meet to a diver with higher DDs and lower scores.

In competition, divers must submit their lists beforehand, and past a certain deadline (usually when the event is announced shortly before it begins) they cannot change their dives under any circumstances. If they fail to perform the dive announced, even if they physically cannot execute the dive announced or even if they perform a more difficult dive, they will receive a score of zero. Under exceptional circumstances, a re-dive may be granted, but this is exceedingly rare (usually for very young divers just learning how to compete, or if some event outside the diver's control has caused them to be unable to perform).

There are some American meets which will allow changes of the position of the dive even after the dive has been announced immediately before execution, but these are an exception to the rules generally observed internationally.

Generally, NCAA rules allow for dives to be changed while the diver is on the platform, but the diver must request the change directly after the dive is announced. This applies especially in cases where the wrong dive is announced. If the diver pauses during his or her hurdle to ask for a change of dive, it will be declared a balk and the change of dive will not be permitted. This can sometimes be dangerous.

Springboard Diving:

A springboard or diving board is used for diving and is a board that is itself a spring, i.e. a linear flex-spring, of the cantilever type.

Springboards are commonly fixed by a hinge at one end (so they can be flipped up when not in use), and the other end usually hangs over a swimming pool, with a point midway between the hinge and the end resting on an adjustable fulcrum.Springboard materials:

Adjustment of the spring constant:

Counter-intuitive user-interface:

Note - Standing behind or in front of the knob, rather than directly above it, will give you better leverage to move the fulcrum. This is accomplished by holding on to the hand rails and leaning the body a few degrees, then placing your foot as low as possible on the knob. In this way, it is possible to move even the most difficult fulcrum.

The spring constant of a springboard is usually adjusted by way of a fulcrum that is located approximately mid way along the springboard. Springboards are usually operated in a “linear regime” where they approximately obey Hooke's law. When loaded with a diver, the combination of the diver's approximately constant mass, and the constant stiffness of the spring(board) result in a resonance frequency that is adjustable by way of the “spring constant” (set by the fulcrum position).

The fulcrum usually travels over a range of approximately 0.75 metres (30 inches), and is set by way of a knob that is approximately 0.35 metres (14 inches) in diameter. To stiffen the spring (as if tightening it), the knob is usually turned counter clockwise. This is counter intuitive, since usually things are tightened by turning clockwise. Additionally, if standing on the springboard, it is difficult to push the wheel with the foot, because the top of it needs to turn the other way from the way it moves. This is because the gearlike mechanism (usually a "soft gear" made of rubber) is on the board and not the base, so the wheel pivots against the board when rotated. Thus users often need to bend down and set the wheel, or come down from the board to set the wheel. Thus it would be much better if the gearing were on the base so that the wheel could be pushed with the foot, but tradition (consistency from board to board) dictates maintaining a "backwards" convention.

Acrobatics in Sports:

Dive numbers:

The first digit of the number indicates the dive group as defined above.

For groups 1 to 4, the number consists of three digits and a letter of the alphabet. The third digit represents the number of half-somersaults. The second digit is either 0 or 1, with 0 representing a normal somersault, and 1 signifying a "flying" variation of the basic movement (i.e. the first half somersault is performed in the straight position, and then the pike or tuck shape is assumed). No flying dive has been competed at a high level competition for many years.
For example:

• 101A - forward dive straight

• 203C - back one-and-a-half somersaults, tuck

• 307C - reverse three-and-a-half somersaults, tuck

• 113B - flying forward one-and-a-half somersaults, pike

• 5211A - back dive, half twist, straight position.

• 5337D - reverse one and a half somersaults with three and a half twists, in the Free position.

For example:

• 600A - armstand dive straight

• 612B - armstand forward somersault pike

• 624C - armstand back double somersault tuck

Until the mid 1990s the tariff was decided by the FINA diving committee, and divers could only select from the range of dives in the published tariff table. Since then, the tariff is calculated by a formula based on various factors such as the number of twist and somersaults, the height, the group etc., and divers are free to submit new combinations. This change was implemented due to the fact that new dives were being invented too frequently for an annual meeting to accom-modate the progress of the sport.

Trajectory of the Dive:

The greatest possible height that can be achieved is desirable for several reasons:

• the height attained is itself one of the factors that the judges will reward.

• a greater height gives a longer flight time and therefore more time to execute maneuvers.

• for any given clearance when passing the board, the forward travel distance to the entry point will be less for a higher trajectory.

The opening of the body for the entry does not stop the rotation, but merely slows it down. The vertical entry achieved by expert divers is largely an illusion created by starting the entry slightly short of vertical, so that the legs are vertical as they disappear beneath the surface. A small amount of additional tuning is available by 'entry save' techniques, whereby underwater movements of the upper body and arms against the viscosity of the water affect the position of the legs.

Twisting in a Dive:

The rules state that twisting 'must not be generated manifestly on take-off'. Consequently, divers must use some of the somersaulting angular momentum to generate twisting movements. The physics of twisting can be explained by looking at the components of the angular momentum vector.


As the diver leaves the board, the total angular momentum vector is horizontal, pointing directly to the left for a forward dive for example. For twisting rotation to exist, it is necessary to tilt the body sideways after takeoff, so that there is now a small component of this horizontal angular momentum vector along the body's long axis.

The tilting is done by the arms, which are outstretched to the sides just before the twist. When one arm is moved up and the other is moved down (like turning a big steering wheel), the body reacts by tilting to the side, which then begins the twisting rotation. At the completion of the required number of twist rotations, the arm motion is reversed (the steering wheel is turned back), which removes the body's tilt and stops the twisting rotation.

An alternative explanation is that the moving arms have precession torque on them which set the body into twisting rotation. Moving the arms back produces opposite torque which stops the twisting rotation.

For Group 5, the dive number has 4 digits. The second digit indicates the group (1-4) of the underlying movement; the third digit indicates the number of half-somersaults, and the fourth indicates the number of half-twists.

For Group 6 - Armstand - the dive number has either three, four or five digits: Three digits for dives without twist and four for dives with twists.

For twisting Armstand dives, the dive number again has 4 digits, but rather than beginning with the number 5, the number 6 remains as the first digit, indicating that the "twister" will be performed from an Armstand. The second digit indicates the direction of rotation - as above, the third is the number of half-somersaults, and the fourth is the number of half-twists:

All of these dives come with DD (degree of difficulty); this is an indication of how difficult/complex a dive is. The score that the dive receives is multiplied by the DD (also known as tariff) to give the dive a final score. Before a diver competes they must decide on a "list"; this is a number of optional dives and compulsory dives. The optionals come with a DD limit, which means that a diver must select X number of dives and the combined DD limit must be no more than the limit set by the competition/organization etc.

The magnitude of angular momentum remains constant throughout the dive, but since
Dives with multiple twists and somersaults are some of the most spectacular movements, as well as the most challenging to perform.

Dive Entry:

The rules state that the body should be vertical, or nearly so, for entry. The arms must be beside the body for feet-first dives, which are typically competed only on the 1m springboard and only at fairly low levels of competition, and extended forwards in line for "head-first" dives, which are much more common competitively. It used to be common for the hands to be interlocked with the fingers extended towards the water, but a different technique has become favoured during the last few decades. Now the usual practice is for one hand to grasp the other with palms down to strike the water with a flat surface. This creates a vacuum between the hands, arms and head which, with a vertical entry, will pull down and under any splash until deep enough to have minimal effect on the surface of the water (the so-called "rip entry"). Once a diver is completely under the water they may choose to roll or scoop in the same direction their dive was rotating to pull the splash away from the channel that they have just created.

Heights of springboards:

Modern springboards are made out of a single-piece extrusion of aircraft-grade aluminum. The Maxiflex Model B, the board used in all major competitive diving events, is made out of such aluminum, and is heat treated for a yield strength of 50,000 psi. The slip-resistant surface of the board is created using an epoxy resin, finished with a laminate of flint silica and alumina in between the top coats of resin. This thermal-cured resin is aqua-colored to match the water of a clean pool.



Springboards are usually located either 1.0 metre or 3.0 metres above the water surface. It is very seldom that one is mounted at a height other than these two standard heights.  Some years ago, springboards, usually made of wood, were located at heights of either 10 feet (approximately 3m), or 20 feet (approx. 6m), above the water.
For example:



Acrobatics is the performance of extraordinary feats of balance, agility and motor coordination. It can be found in many of the performing arts, as well as many sports. Acrobatics is most often associated with activities that make extensive use of gymnastic elements, such as “acro dance”, circus, and gymnastics, but many other athletic activities—such as ballet and diving—may also employ acrobatics. Although acrobatics is most commonly associated with human body performance, it may also apply to other types of performance, such as aerial acrobatics.

In non-twisting armstand dives, the second digit indicates the direction of rotation (0 = no rotation, 1 = forward, 2 = backward, 3 = reverse, 4 = inward) and the third digit indicates the number of half-somersaults. Inward-rotating armstand dives have never been performed, and are generally regarded as physically impossible.

e.g. 6243D - armstand back double-somersault with one and a half twists in the free position

Mechanics of diving:

Control of diving rotation:

In competition, the dives are referred to by a schematic system of three- or four-digit numbers. The letter to indicate the position is appended to the end of the number.

At the moment of take-off, two critical aspects of the dive are determined, and cannot subsequently be altered during the execution. One is the trajectory of the dive, and the other is the magnitude of the angular momentum.

The speed of rotation - and therefore the total amount of rotation - may be varied from moment to moment by changing the shape of the body, in accordance with the law of conservation of angular momentum.
The center of mass of the diver follows a parabolic path in free-fall under the influence of gravity (ignoring the effects of air resistance, which are negligible at the speeds involved).
Since the parabola is symmetrical, the travel away from the board as the diver passes it is twice the amount of the forward travel at the peak of the flight. Excessive forward distance to the entry point is penalized when scoring a dive, but obviously an adequate clearance from the diving board is essential on safety grounds.

angular momentum = rotational velocity × moment of inertia,

the moment of inertia being larger when the body has an increased radius; the speed of rotation may be increased by moving the body into a compact shape, and reduced by opening out into a straight position.
Since the tucked shape is the most compact, it gives the most control over rotational speed, and dives in this position are easier to perform. Dives in the straight position are the hardest, since there is almost no scope for altering the speed, so the angular momentum must be created at take-off with a very high degree of accuracy. (A small amount of control is available by moving the position of the arms and by a slight hollowing of the back).

copyright 2014, Anne Shier.  All rights reserved.