Refining the variability and control of NSWIS divers somersaults

Australia’s divers will look to continue their medal-winning run and slow the recent dominance of the Chinese as they compete at the first outdoor diving venue since the Atlanta 1996 Games in Rio.

Prior to the Games we caught up with NSWIS Research Assistant Cherie Walker to discuss the papers that she has published in relation to the Variability and the Control of Rotation during Springboard Diving.

The study utilised new technology to analyse the movement of the athletes, with the NSWIS being the first to use this technology in the sport of diving.

What was the objective of the study?

The study aimed to explore the variability in angular velocity profiles across multiple somersault dives.

During a somersault dive, divers leave the springboard with a given amount of angular momentum and maintain a constant momentum until water entry. When performing dives that include multiple somersaults, divers maintain a tight tuck or pike position to reduce their moment of inertia, and therefore to assist rotational speed before kicking out. The diver then aims to achieve an extended and vertical position at the point of water entry with minimum splash.

Therefore, being able to coordinate, control and adjust movement presents a substantial challenge for divers. Understanding and identifying the process by which it can be achieved has important implications, least of all for coaching and performance optimisation.

This study firstly explored the degree of variability in angular velocity profiles across multiple somersault dive attempts.

Secondly, it examined whether divers actively controlled the timing of the kick out in accordance with variations in the velocity of rotation in an effort to assure accurate and reliable water entry.

What methods did you use to carry out the study?

Four international divers participated in the study. Each completed 4-6 forward somersault dives at their highest degree of difficulty from a three metre springboard.

Two divers performed the three and a half somersault dive in a pike position and two performed the four and a half somersault dive in a tuck position.

What technology did the study utilise?

The angular velocity was measured using a waterproof inertial measurement unit (IMU) with embedded gyroscope strapped to the lower back using a transparent film dressing.

What did you find as a result of your study?

Each diver produced a consistent pattern of performance, with high similarity between divers performing the same respective dive type.

Total dive time was consistent with standard deviations and all participants displayed low variability between trials in angular velocity and in plateau duration time.

All participants except one produced less variability between trials in their angular velocity measures than they did for variability in the plateau duration.

Between 70-83% of the total rotation for each dive was produced during the plateau region where divers held a fixed tuck/pike position.

There was relatively low variability in total rotation compared with the amount of variability before the plateau, during the plateau or after the plateau. The total rotation represents low outcome variability as you would expect for experienced performers.

A strong correlation was evident for all divers between plateau duration and the amount of rotation during this period. Correlations between the amount of rotation and angular velocity were comparatively weaker suggesting that tuck duration had a greater association with the amount of rotation achieved.

Negative correlations were found for all divers between the amount of rotation occurring before the end of the plateau and the amount of rotation after the plateau. Part of this effect would occur largely because, if divers held the tuck longer, producing more rotation during the plateau, then there would be less time available for rotations to occur after the plateau.

What are your conclusions from the study?

A high degree of consistency in angular velocity appears necessary when performing multiple somersaults as part of a successful dive.

Divers may have regulated the duration and velocity of their somersaults to within 1% of variability because to do otherwise would have resulted in a ten degree change in total rotation for the dive.

There is no explicit evidence to suggest that divers were able to intentionally manipulate the timing of opening out from a tuck/pike position in response to variations in velocity of rotation. Thus, we remain reserved in understanding and recommending whether and how diving movements can be controlled prior to water entry.

The ‘air time’ a diver has to perform additional somersault rotations is of key importance in order to execute a dive with a perfect entry position. For example, a diver wanting to perform the 4½T must have a combination of mechanical (i.e. take off hip angles & angular velocity) and physical (i.e. strength) elements to provide them with adequate time of flight. If a diver does not reach the required level of these elements they are at risk of entering the water under rotated and therefore losing points from the judges.

To progress from this position, it is proposed that examining dives with a lower number of required rotations, and consequently with a lower degree of difficulty, may provide better insight as to whether skilled divers can controllably modify their angular velocity in mid-flight to affect the angle of water entry.