Techniques Used by Elite Gymnasts in the 1992 Olympic Compulsory Dismount from the Horizontal Bar

The purpose of this study was to identify the mechanical factors that are crucial to a successful double salto backward tucked dismount from thehorizontal bar. The subjects were 35 American and 43 Japanese gymnasts competing in their respective 1990 national gymnastics championships. A 16-mm camera, placed with its optical axis parallel to the horizontal bar and operating at 100 Hz, was used to record the performances of the subjects. Significant correlations indicated that a large vertical velocity at bar release, which ensures great height and long time of flight, is important. Successful performance is also likely when efforts are made to (a) achieve the tightest tuck position during the salto backward near the peak of flight, (b) extend the body rapidly and fully early in rotation before the vertical body position is reached well above the bar, (c) maintain the extended body position during the remainder of the flight to display body style for virtuosity bonus points, and (d) simultaneously prepare for a controlled landing on the mat.

Spectral Analysis of Impact Shock during Running

The purpose of this study was to determine the effects of increasing impact shock levels on the spectral characteristics of impact shock and impact shock wave attenuation in the body during treadmill running. Twelve male subjects ran at 2.0, 3.0, 4.0, and 5.0 m s−1on a treadmill. Axial accelerations of the shank and head were measured using low-mass accelerometers. The typical shank acceleration power spectrum contained two major components which corresponded to the active (5–8 Hz) and impact (12–20 Hz) phases of the time-domain ground reaction force. Both the amplitude and frequency of leg shock transients increased with increasing running speed. Greatest attenuation of the shock transmitted to the head occurred in the 15–50 Hz range. Attenuation increased with increasing running speed. Thus transmission of the impact shock wave to the head was limited, despite large increases in impact shock at the lower extremity.

Hub Movement during the Swing of Elite and Novice Golfers

Many golf coaches refer to a focal point or “hub” of a golf swing and encourage players to imagine the clubhead rotating about this point. The purpose of this study was to locate the hub of the swings of elite (handicaps 0–5) and novice golfers. Six novice and six elite players (all male) each performed 10 swings with the 3-wood provided. Motions of reflective markers attached to the vertex and chin of the subject and three points along the shaft of the club were recorded on videotape. The position of the hub at sampled instants during the swing was defined by the intersection of normals to the clubhead path. Among elite players the hub was not fixed and the pattern of hub movement was consistent. The radius of the hub to the clubhead reached a maximum near impact. Novice players tended to achieve maximum radius after impact and the hub patterns were inconsistent.

A New Electromechanical Ski Binding with Release Sensitivity to Torsion and Bending Moments Transmitted by the Leg

This paper describes the design of a new electromechanical ski binding whereby release in both twist and forward bending is controlled electronically and the release level in twist is modulated electronically based on the neural stimulation of muscles in the quadriceps group. To provide signals for controlling release in the two modes, the binding incorporates two dynamometers. Each dynamometer measures loads that have been shown to correlate strongly (r2>0.90) to torsional and bending moments at the lower leg injury sites. Although the binding consists of both a toepiece and heelpiece, the toepiece does not permit release of the boot from the ski in the twist mode but rather serves as one of the dynamometers. Consequently the heelpiece was designed to provide the release function in both modes. Release is realized by a low-force solenoid that actuates a multilink trigger mechanism. To prove feasibility, a prototype was constructed and evaluated.

Objective Biomechanical Determination of Tennis Racket Properties

Several biodynamical properties of tennis rackets such as vibrational characteristics, direction control, and the coefficient of restitution depend critically on the constraining mode of the handle. The racket response to ball impact differs fundamentally for rigid mechanical clamping of the handle and for hand-held gripping. In order to test objectively the biodynamical characteristics of tennis rackets under standardized but biomechanically realistic conditions, the use of a mechano-electronic replica of the human hand/arm system, termed manusimulator, is suggested. Sample test results of the vibrational characteristics of a specific tennis racket and of the coefficients of restitution of several rackets provide proof of the reproducibility and reliability of the test results so obtained. The results were compared with those obtained using human test players. The latter subjective method yielded data with excessively large coefficients of variation around 84% and was found to be unsuitable for determining tennis racket properties objectively. It is concluded that the standardizable manusimulator testing procedure offers a valuable alternative to subjective testing methods for determining tennis racket parameters.

Archery Bow Grip Force Distribution: Relationships with Performance and Fatigue

Archery instructors believe that force distribution (FD) between the hand and bow grip can have a considerable effect on arrow flight, but there is no empirical support for this speculation. This study examined FD on the bow grip in experienced archers and explored the possible relationships between FD, performance, and fatigue. FD was quantified for 15 experienced archers (8 highly skilled [HS] and 7 less skilled [LS]) using 15 unobtrusive force sensors as each archer completed 72 shots. Arrow position relative to the target center, estimated net moments and moment arms about vertical and horizontal axes through the grip, and shot-to-shot variability in the estimated moments and moment arms were computed for three blocks of six shots. Results demonstrated that (a) estimated moments and moment arms were not consistently related to observed vertical or horizontal deviations in arrow position, (b) there were no systematic differences in FD between HS and LS archers, (c) fatigue had no quantifiable effect on FD, and (d) HS archers displayed less shot-to-shot variability in vertical FD than LS archers, but similar variability horizontally. Results did not support the above-noted common belief of archery instructors.

The Technique of Elite Flatwater Kayak Paddlers Using the Wing Paddle

The technique of elite New Zealand kayak paddlers using the Norwegian wing paddle was analyzed to identify factors leading to success. Five male New Zealand kayak paddlers were filmed with two high-speed cinematographic cameras. Paths of the blade tip and joint centers were determined from film data. Velocities ranged from 4.63 to 5.38 m/s. Stroke frequency ranged from l .93 to 2.26 cycles/s. Results indicated that the more successful paddlers, based on previous competitive performances, had similar movement patterns and blade paths and that these differed from those of less successful paddlers. Their blade tip and joint center paths were more consistent across trials. More successful paddlers entered their blade well forward and closer to the longitudinal axis of the kayak than did less successful paddlers, and moved the blade a large distance laterally from the kayak and only a small distance backward with respect to the water.

Dynamics of the Interactions between Ball, Strings, and Racket in Tennis

The dynamical interactions in tennis between ball, strings, and racket, during ball impact and immediately after, are modeled by a system of nonlinear ordinary differential equations that include both damping and elastic properties. During impact, the time history of the deflections, velocities, and forces in all parts of the system were calculated. Some simple experiments were done to determine the elastic and damping properties of the ball and strings, and to verify the theory in the case of a ball rebounding from the strings of a clamped racket head. Among the findings is that there is a trampoline effect even for a clamped racket head. Most interesting is that the rebound velocity of the ball can be increased, the mechanical energy transmitted to the racket can be reduced, and the maximum force transmitted to the holder of the racket can be reduced, all by increasing the damping in the racket.

A Dual Piezoelectric Bicycle Pedal with Multiple Shoe/Pedal Interface Compatibility

In response to the popularity of clipless bicycle pedals with float designs, an instrumented force pedal system with multicompatibility for different shoe/pedal interfaces is presented. A dual piezoelectric element pedal has been modified for use with popular clipless pedal interfaces. The dual transducer arrangement permits measurement of three components of uniaxial load, location of the applied load, and calculation of the moment Mz about an axis through the position of the applied load and orthogonal to the pedal surface. Quantification of lower extremity kinetics using float feature pedals and the investigation of the pathomechanics of lower extremity cycling overuse injuries, especially knee injuries, is warranted. Qualitative descriptions of lower extremity pathomechanics related to overuse injuries have suggested that foot constraint may induce undesirable knee kinematics and kinetics. The instrumented force pedal system described here permits a comparison between pedal kinematics and kinetics of popular shoe/pedal interfaces with varying degrees of float allowance.