Twisting techniques used by competitive divers

At the 1991 World Student Games, eight reverse 1½ somersault dives with 2½ twists were recorded during the men's finals in the 1 m and 3 m springboard diving competitions using two video cameras. Angles describing body configuration were determined from video data and were input, together with initial orientation angle values and angular momentum components, into a computer simulation model of aerial movement in order to predict body orientation in space. Mean absolute deviations between simulation and video after the completion of one twist were 0.02 rev for somersault, 2.3° for tilt and 0.04 rev for twist. Contributions to the tilt angle after one twist were used as measures of the twisting potential of various techniques and were determined using simulations based on modifications of the video data. Seven of the eight competitors produced the majority of the tilt using aerial techniques which were predominantly asymmetrical movements of the arms and hips, although the mean contribution from contact techniques amounted to one‐third of the total tilt

The simulation of aerial movement—III. The determination of the angular momentum of the human body

A method is presented for determining the angular momentum of the human body about its mass centre for general three–dimensional movements. The body is modelled as an 11 segment link system with 17 rotational degrees of freedom and the angular momentum of the body is derived as a sum of 12 terms, each of which is a vector function of just one angular velocity. This partitioning of the angular momentum vector gives the contribution due to the relative segmental movement at each joint rather than the usual contribution of each segment. A method of normalizing the angular momentum is introduced to enable the comparison of rotational movements which have different flight times and are performed by athletes with differing inertia parameters. Angular momentum estimates were calculated during the flight phases of nine twisting somersaults performed on trampoline. Errors in film digitization made large contributions to the angular momentum error estimates. For individual angular momentum estimates the relative error is estimated to be about 10% whereas for mean angular momentum estimates the relative error is estimated to be about 1%

The biomechanics of twisting somersaults. Part II: contact twist

A simulation model and a rigid body model are used to investigate twisting initiated during the takeoff or contact phase. It is shown that it is possible to produce a full twist solely by building up angular momentum in the arms during the contact phase. This method is only half as effective as building up momentum in the whole body during contact. The introduction of twist into a somersault changes the somersault rate by less than 1%. By timing arm adduction appropriately, it is possible to take advantage of nutation and boost the initial value of the tilt angle and so obtain a greater twist rate. Twist may be stopped by the action of piking, since the motion changes from the twisting mode to the wobbling mode of rigid body motion. Transition to and from these two modes can be used to increase or decrease the tilt angle and twist rate

Twisting double somersault high bar dismounts

At the 1988 Seoul Olympic Games, four double somersault dismounts with one twist and four double somersault dismounts with two twists were filmed using two 16 mm cameras during the men's horizontal bar competitions. Contributions to tilt angle reached at the midtwist position, determined using computer simulations based on modifications of the data obtained from film, were used as measures of the twisting potential of various techniques. The amount of tilt produced was greater when total twist was greater and when the body was tucked rather than straight. The twisting techniques used varied with the timing of the twist within the two somersaults. Contact contributions were larger when there was more twist in the first somersault. When there was little or no twist in the first somersault, the major contribution came from aerial techniques that comprised mainly arm movements and asymmetrical hip movements in the flight phase

The simulation of aerial movement—II. A mathematical inertia model of the human body

A mathematical inertia model which permits the determination of personalized segmental inertia parameter values from anthropometric measurements is described. The human body is modelled using 40 geometric solids which are specified by 95 anthropometric measurements. A ‘stadium’ solid is introduced for modelling the torso segments using perimeter and width measurements. This procedure is more accurate than the use of elliptical discs of given width and depth and permits a smaller number or such solids to be used. Inertia parameter values may be obtained for body models of up to 20 segments. Errors in total body mass estimates from this and other models are discussed with reference to the unknown lung volumes

Twisting techniques used in freestyle aerial skiing

At the 1988 Calgary Winter Olympics, six triple somersaults with three twists or four twists were filmed using two cameras. Angles describing body configuration and orientation were determined and were used as input into a computer simulation model of aerial movement. It was found that the twist angle of each simulation deviated from the corresponding angie obtained fTom film hy less than 0.08 revolutions during the first somersault of each movement. Contributions to the tilt angle after one somersault were determined using simulations based on modifications ofthe film data. It was found that of the six competitors, two initiated the twist during the takeoff phase, two initiated the twist during the aerial phase, and two used a combination of both methods

The biomechanics of twisting somersaults. Part III: aerial twist

A simulation model and a rigid body model are used to evaluate aerial twisting techniques. It is found that when somersault is not present, a number of cycles of segment counter-rotation are required to produce one twist. When somersault is present, twist may be introduced by producing tilt using asymmetrical movements of the arms, chest or hips about the sagittal plane. The same asymmetrical movements may be used to remove tilt, although the effectiveness of these techniques is dependent upon body configuration and the direction of somersault

The biomechanics of twisting somersaults. Part IV: partitioning performances using the tilt angle

A method is presented for determining the contributions made by contact and aerial twisting techniques in filmed performances of twisting somersaults. An 11-segment simulation model is used to determine the effects of removing asymmetries about the sagittal plane. Tilt contributions are determined for four competitive movements performed by an elite trampolinist. It is found that even in movements in which the twist is evident at takeoff, aerial techniques make a greater contribution than contact techniques

The limits of aerial twisting techniques in the aerials event of freestyle skiing

In the aerials event of freestyle skiing, athletes perform three somersaults with up to five twists. This study investigated the twisting limits of such movements using a computer simulation model of aerial movement. The abilities of various asymmetrical arm and hip techniques to produce twist during flight were investigated using 10 simulations to maximise twist and allow reorientation prior to landing. It was found that 4-6 twists could be produced during three somersaults. The main limiting factor was the increased whole body frontal moment of inertia due to the equipment which restricted the amount of tilt resulting from an asymmetrical arm movement. It was concluded that reductions in equipment mass might make such movements easier to achieve but would be unlikely to allow advances beyond the limits found

A method for obtaining three-dimensional data on ski jumping using pan and tilt cameras

A method is presented for the three-dimensional analysis of ski jumping using two pan and tilt cameras. In each film frame two reference markers are digitized and identified so that a pseudo focal length and three angles defining camera orientation can be calculated from a knowledge of the positions of camera and markers. In each film frame 12 body landmarks are digitized and the films taken by the two cameras are synchronized using the digitized displacement data. The time histories of the center of mass location and 15 angles describing the orientation and configuration of the jumper are calculated. Digitization errors lead to an error of 0.05 m in center of mass location and an error of 1° in orientation angle