TAKE-OFF CHARACTERISTICS OF DOUBLE BACK SOMERSAULTS ON THE FLOOR

Backward take-offs are one of the most important and frequently used components of a floor routine in artistic gymnastics and usually occur at the beginning, middle, and at the finish of a routine. They also initiate the linear and rotational impulses for multiple somersaults with various body positions with or without twists. This study was undertaken to supplement the work done previously by Brueggemann (1983, 1987, 1994), Hwang et al. (1990) and Knoll(1993). The purpose of the study specifically, was to investigate the biomechanical characteristics of dynamic take-offs in double backward somersaults performed by ten male and eight female gymnasts on the floor at the world gymnastics championships in Brisbane, 1994. Data was captured at 50Hzby two video cameras; this permitted the calculation of 3D kinematic data. Mean and standard deviations of selected kinematic and temporal parameters were calculated in order to: compare differences of biomechanical characteristics between male and female gymnasts, identify the differences in take-offs between the different types of double back somersaults performed, and to compare the data to those reported previously. Analysis of the data for both male and female gymnasts revealed, that the most important performance factor determining somersault height, the vertical velocity of the CM, changed from 1.17±0.46 and2.35±0.60 m/s at touch-down to 4.2±0.46 and 3.54±0.85 m/s at take-off, respectively. The vertical velocity value for the male gymnasts (4.2k0.46 m/s)was lower, assuming their body mass is the same, compared to those of previously reported studies by Brueggemann 4.57 m/s (1983), Hwang et al. 4.46m/s (1990) and Newton et al. 5.8 m/s (1992). This was most likely due to localized leg muscle fatigue; 70% of the analyzed take-offs in this study were performed at the finishing acrobatic series of their floor exercise. Brueggemann(1983, 1987) and Hwang et al. (1990) reported, that the leg muscles played the dominant role in take-offs. The horizontal velocity at touch-down was 4.32 ±0.47and 4.05±0.47 m/s and decreased to 3.21±0.49 and 2.30±2.27 m/s at take-off, respectively. The take off period was 130 and 120 ms, respectively for males and females. The touch-down and take-off angles of the CM to ground contact and the horizontal was 64.1±6.1, 69.7±5.9 and 88.1±3 .0 and 90.6±5.0,respectively. Preliminary results from the angular momentum calculations confirm the values of previously reported studies by the above authors

LANDING ChARACTERISTICS OF DOUBLE BACK SOMERSAULTS ON THE FLOOR

One of the most frequently used components of a floor exercise are the landings which occur at the beginning, anywhere in between, and at the finish of the exercise. This study examined the biomechanical characteristics of double back somersault landings at the beginning, during, and at the end of a floor exercise. Performances of ten selected male gymnasts at the World Gymnastic Championships 1994 in Brisbane, were chosen. Kinematic data was captured at50 Hz through 3-D videorecordings during competitions, with the videocameras positioned on the catwalks above the floor of the competition venue. The analysis included mean and standard deviations of selected kinematic and temporal parameters in order to identify the biomechanical characteristics in landings, and to establish a profile for stable competition landings on floor, which should also comply with specific competition guidelines as set out by the FIG code of points. Analysis of the data revealed, that the displacement h m maximum CM height before the landing (2.18 ±0.16 m) to CM height at landing (0.88±0.13 m) was 1.3 ±0.1 1 m. The vertical and horizontal impact velocities were 4.2±0.46 and 3.21±0.49 m/s. The mean knee angles at landing (touch-down) were 153" and at minimum CM height were 98", a 55"knee angular landing force absorption over 0.12 sec. landing phase duration. The videorecordings of the individual landing performances were carefully reviewed to qualitatively investigate the completion of the second salto of the double back somersault before the landing. The better performances showed a reasonable extension of the body or a kick out before the landing, and the landing was actively anticipated through proper feet placement. Poor performances resulted in a slow second salto extending the hip and knee joints hurriedly into the landing surface. The mean angles between CM to toe and the horizontal at landing (touch-down) were 69". The mean angles between trunk and the horizontal and thigh to the horizontal at landing (touch-down) were 22and 84", respectively. Selected parameters of the results presented in this study may be used to form a representative biomechanical profile for floor landings

BIOMECHANICAL ANALYSIS OF THE "O'NEIL"

Paul O'Neil was the first gymnast to perform the "stretched double felge backward to forward swing in hang on the rings" at the World Gymnastic Championships in Brisbane,l994. This skill can be placed in the movement category (Brueggemann, 1994) of (backward) rotations in the vertical plane with a flexible horizontal axis of rotation. The O'Neil is listed in the current FIG code of points as a D-part in the difficulty category. The purpose of this case study is to provide a descriptive kinematic analysis and a description of the technique employed by O'Neil performing the "O'Neil". This dynamic skill is initiated by generating rotational kinetic energy during the downward swing phase from a momentary handstand position. Thus the angular velocity of the body in the sagittal plane is maximized simultaneously with the maximisation of the moment of inertia relative to the body's centre of gravity. The maximum vertical velocity during the downswing phase before the beginning of the O'Neil was -4.2 1 m/s and reached a value of 3.91 m/s 0.24 seconds after the beginning of the up-swing. Ludwig (1992) suggests that the rotation of the trunk around an axis through both shoulder joints becomes the most important determining factor for the swing on the rings. The data revealed, that during the up-swing the hip joint reached its lowest value (flexion) distinctly in advance of the shoulder joints. Once the arm-trunk (shoulder) angle reached its minimum value, the hip joint reached hyper extension throughout the skill. Also, the arms and shoulders remained under the rings, which was consistent with the findings of Nissinen (1983). The CG displacement at the beginning of the skill, the start of the upswing to its highest value was 1.75 m. The analysis of the joint angle movements provides an inside into the mechanism for increasing rotation. The angular velocity over time of the hip angle was -949&g/sec and for the shoulder angle was -670 &g/sec. The p o w d closing ofthe arm-trunk angle is the most important technical component for thesuccessful performance of the O'Neil. The duration of the skill was 1.46 sec from the beginning of the upward swing to the vertical body position at completion of the skill. It seems, that only O'Neil, who has that natural" anthropometric make-up", is able to perform such an exciting, unique, and novel skill

LANDING KINEMATICS OF HORIZONTAL BAR DISMOUNTS

Dismounts from the horizontal bar require the dissipation of substantial velocities and therefore large forces. The maximum heights from dismounts are seen to be in the order of 4m or more. Kerwin et al. (1990) reported that maximum heights for double somersault dismounts -ranged from 3.45 to 3.73m,and for triple somersault dismounts, 3.89 to 4.08m. The purpose of this study was to investigate the biomechanical characteristics of succesful horizontal bar landings. Performances of six out of eight male finalists from the individual apparatus finals on horizontal bar at the World Gymnastic Championships1994, Brisbane, were chosen. The dismounts were recorded at 50 Hz during competitions, with the video cameras positioned on the catwalks above the floor of the competition venue. The analysis included mean and standard deviations of selected kinematic and temporal parameters in order to identify successful competition landing techniques. The recordings of the individual dismounts and subsequent landing performances were reviewed to qualitatively investigate the completion of the last salto of the double and triple back somersaults before the landing. The double back layout dismounts showed aback arched shape for most of the flight phase before re-piking in preparation for the landing. Analysis of the data revealed a mean maximum CM height during dismount, before the landing, of 3.06 m and an impact velocity at landing of-6.48 d s . Brueggemann et al. (1994), reported mean release velocities of 4.79 st 0.33 m/s for double tucked back somersault, 4.04 f 0.1 m/s for double layout back somersault, and 5.08 f 0.31 d s for triple tucked back somersault dismounts, which compares to the impact velocity of this study. The knee angle at landing was 156" and minimum knee angle during landing was 87". This available range of motion of 69" knee flexion with a landing phase duration of 0.14sec7 was a significant factor for the preparation phase of successful landings. The mean CM to ground contact and the horizontal was 87". Trunk to horizontal at landing was 134", and thigh to horizontal at landing was 107". Selected parameters of the results presented in this study may be used to form a representative biomechanical profile for horizontal bar landings

TAKE-OFF KINEMATICS OF BEAM DISMOUNTS

Beam dismounts require great courage, the highest level of precision of movement, and a special take-off technique. They have only marginally increased in difficulty in recent years, however, their technical execution has reached close to technical perfection. The technical criteria for the execution of successful beam dismounts are essentially similar to those of floor take-offs. Nevertheless, the configurations of the beam, its small width (10cm) and surface stiffness relative to the floor, put considerable limitations on the performer and subsequently change the take-off technique somewhat greatly. The purpose of the study was to investigate the biomechanical characteristics of dynamic beam dismounts performed by eight female gymnasts at the World Gymnastics Championships in Brisbane, 1994. Data was captured at 50 Hz by two video cameras positioned on the catwalks above the floor of the competition venue, which permitted the calculation of 3D kinematic data. Mean and standard deviations of selected kinematic and temporal parameters were calculated in order to: identify special biomechanical characteristics of takeoff technique for the balance beam, identify the differences in take-offs between the different types of dismounts performed, and to compare the data to those reported previously. Analysis of the data revealed, that the most important performance factor determining somersault height, the vertical velocity at take-off of the CM, ranged from 1.84 to 3.04 m/s, with a mean value of 2.49 ±0.40 m/s, which is considerably lower then for floor take-offs. The mean values for the horizontal velocity at take-off were 1.5

Phoretic Motion of Spheroidal Particles Due To Self-Generated Solute Gradients

We study theoretically the phoretic motion of a spheroidal particle, which generates solute gradients in the surrounding unbounded solvent via chemical reactions active on its surface in a cap-like region centered at one of the poles of the particle. We derive, within the constraints of the mapping to classical diffusio-phoresis, an analytical expression for the phoretic velocity of such an object. This allows us to analyze in detail the dependence of the velocity on the aspect ratio of the polar and the equatorial diameters of the particle and on the fraction of the particle surface contributing to the chemical reaction. The particular cases of a sphere and of an approximation for a needle-like particle, which are the most common shapes employed in experimental realizations of such self-propelled objects, are obtained from the general solution in the limits that the aspect ratio approaches one or becomes very large, respectively.Comment: 18 pages, 5 figures, to appear in European Physical Journal

Systematic model behavior of adsorption on flat surfaces

A low density film on a flat surface is described by an expansion involving the first four virial coefficients. The first coefficient (alone) yields the Henry's law regime, while the next three correct for the effects of interactions. The results permit exploration of the idea of universal adsorption behavior, which is compared with experimental data for a number of systems

The PHENIX Experiment at RHIC

The physics emphases of the PHENIX collaboration and the design and current status of the PHENIX detector are discussed. The plan of the collaboration for making the most effective use of the available luminosity in the first years of RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program available at http://www.rhic.bnl.gov/phenix

Heavy Quarks and Heavy Quarkonia as Tests of Thermalization

We present here a brief summary of new results on heavy quarks and heavy quarkonia from the PHENIX experiment as presented at the "Quark Gluon Plasma Thermalization" Workshop in Vienna, Austria in August 2005, directly following the International Quark Matter Conference in Hungary.Comment: 8 pages, 5 figures, Quark Gluon Plasma Thermalization Workshop (Vienna August 2005) Proceeding

Single Electrons from Heavy Flavor Decays in p+p Collisions at sqrt(s) = 200 GeV

The invariant differential cross section for inclusive electron production in p+p collisions at sqrt(s) = 200 GeV has been measured by the PHENIX experiment at the Relativistic Heavy Ion Collider over the transverse momentum range $0.4 <= p_T <= 5.0 GeV/c at midrapidity (eta <= 0.35). The contribution to the inclusive electron spectrum from semileptonic decays of hadrons carrying heavy flavor, i.e. charm quarks or, at high p_T, bottom quarks, is determined via three independent methods. The resulting electron spectrum from heavy flavor decays is compared to recent leading and next-to-leading order perturbative QCD calculations. The total cross section of charm quark-antiquark pair production is determined as sigma_(c c^bar) = 0.92 +/- 0.15 (stat.) +- 0.54 (sys.) mb.Comment: 329 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm