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.
A system was developed to quantify the on-water forces, impulse, and power generated by a kayak paddlet. The system is lightweight (<1 kg), portable (i.e., it can be used in single [Kl], double [K2], and fours [K4] boats), and does not affect the integrity of either the kayak paddle or the boat. Changes in the strain on the kayak paddle were measured by force transducers attached to the shaft of the paddle, and these signals were then recorded on an FM tape recorder located in the boat. The data were then analyzed by the Kayak Data Acquisition and Analysis System software which graphically presented the paddlers' force time curve as well as a printed tabular report on the paddlers' average force, impulse, work, power, and the instantaneous boat velocity.
Described is the design of a foot/pedal interface intended as a research tool in the study of overuse knee injuries in cycling. The interface enables the systematic variation of factors that may affect loads transmitted by the knee joint. It permits two degrees of freedom of movement, inversion/eversion and abduction/adduction rotations, either separately or in combination. The movement permitted by each degree of freedom can be either free or resisted by spring assemblies. Sample data were collected to demonstrate the function of the foot/pedal interface. With no spring resistance, the interface functioned as intended by allowing free movement of the foot. Significant interaction was seen between the two degrees of freedom, with more motion and a larger absolute mean occurring when both degrees of freedom were allowed simultaneously. This emphasizes the need for a multi-degree-of-freedom interface when undertaking a comprehensive study of the factors affecting loads transmitted by the knee.
Tennis movements are characterized essentially by lateral displacements, thus external load on the lower extremities is created predominantly by friction generated between shoes and playing surfaces. This study analyzed the behavior of frictional forces and torques produced during an open stance forehand using various playing surfaces and different sport shoes. The frictional data were obtained from 12 advanced players returning a tennis ball fired from a ball machine and hitting a large Kistler force plate located at the base line of the tennis court. Using statistical ANOVA techniques, friction was found to be more sensitive to the choice of playing surface than to the choice of tennis shoe. "Fluid" type surfaces displayed the lowest frictional values in most cases. Additionally, comparison of the frictional data collected during the forehand with the measurements from a standardized laboratory test demonstrated that extrapolation of friction results from laboratory to real field conditions may lead to erroneous conclusions.
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.
Ten male recreational runners ranging in age from 20 to 32 years were filmed using 3-D cinematography while running on a treadmill at 3.8 m/s, 4.5 m/s, and 5.4 m/s. The 3-D segment endpoint data were entered into a computer program that computed the segmental contributions to the upward and forward propulsive impulses on the body (lift and drive, respectively) and to the vertical component of angular momentum (H(Z)). The results of two subjects who demonstrated asymmetrical arm action are discussed in detail and compared with the mean results computed over all subjects. The results revealed that the arms possess the potential to compensate for each other and for asymmetries elsewhere in the body.
The purpose of this study was to identify the mechanical factors that are crucial to successful performance of blocking and body control for salto forward and kickout in the handspring and salto forward tucked vault. A 16-mm camera operating at 100 Hz was used to record the performances. The subjects were 51 male gymnasts participating in the 1988 Olympic Games. It was hypothesized that some mechanical factors identified in the model were significantly correlated with successful performance of blocking and body control for salto forward and kickout as rated by the judges. Significant correlations indicated that a large horizontal velocity at touchdown on horse is an important prerequisite for effective blocking and subsequent performance of postflight. The results also indicated that the body's moment of inertia should be minimized by assuming the full tuck position just before or near the peak of flight, which maximizes the time and height available for executing the kickout in midair. The small angular speed of body rotation due to early kickout and the long-held extended body position as it travels a large horizontal distance are not only effective in the expression of artistic amplitude for virtuosity points but are also crucial for control in landing.
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.
This study compared the errors produced with 3-D video and film analysis techniques using the DLT method with fixed cameras when the images cover a wide field of view. The results indicated that with a large field of view (8 meters) the accuracy of video analysis is clearly inferior to that of film analysis. However, within the volume of the control object, both film and video analyses are still precise enough for most practical purposes. Errors were larger in landmarks outside the control object than in the points of the control object. The maximum errors in the calculated positions of external landmarks were particularly large in the video analysis. However, even these rather large errors for points markedly outside the control object may be acceptable. It will depend on the requirements of each particular investigation.
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.
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−1 on 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.
The purpose of this study was to determine the effects of grip width, chest depth, limb lengths, and bar path on the performance of a maximal bench press. Subjects were 24 experienced male weight trainers. Bench press performance was assessed at six different grip widths (G1–G6). Repeated-measures ANOVA with Tukey post hoc comparisons revealed that bench press strength values at the two moderate grip widths (G3 and G4) were significantly greater than either the narrow or wide grip widths. First-order partial correlations showed no significant relationship between strength values and anthropometric variables when adjusted for differences in body weight. Standard two-dimensional cinematographic procedures were used to film a subsample ( n = 6) while bench pressing using G1, G3, and G6. The results of the statistical comparisons of bar path indicated that as grip width increased, the horizontal and vertical distance from the bar to the shoulder decreased.
This study investigated the phenomenon of kinematic asymmetry of the lower limbs in distance runners. The subjects, 29 male distance runners, were recorded by high-speed filming while running on a motor driven treadmill under two experimental conditions (with running shoes and barefoot). Twelve selected kinematic variables were subjected to multivariate statistical analysis. It was demonstrated that the lower limbs of distance runners possess a multifaceted kinematic asymmetry for touchdown and foot contact as well as for the entire phase of foot support of the running stride. Significant kinematic asymmetries were found in the lower leg angle, rearfoot angle, mediolateral velocity of the foot, and in some temporal variables. Contemporary running shoes seem to significantly change the degree of rearfoot control asymmetry observed in normal barefoot running. The findings of the present study confirm previous data suggesting that the phenomenon of kinematic asymmetry in runners is warranted.
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.
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.
The purpose of this study was to determine resultant knee joint forces and moments during a specific movement in Alpine ski racers. The movement analyzed consisted of a landing from a bump and the initiation of recovery (if necessary). Resultant loads were obtained using an inverse dynamics approach. Results of two specific skiers are contrasted, one skier landing in good form, the second skier landing in poor form. The skier landing in poor form exhibited larger knee flexion, and larger knee joint resultant forces and moments than the skier landing in good form. The movement of the skier landing in poor form has been associated with isolated anterior cruciate ligament (ACL) injury. However, the data obtained in,this study do not indicate that either skier was in danger of ACL injury.
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.
The present study explored kinematic adaptation in the lower extremity to running in shoes with 10° valgus and varus midsole perturbations. Rearfoot motion and knee flexion/extension data on nine subjects were collected using a Selspot II system during treadmill running in the two test shoes and in a neutral shoe condition. Maximum pronation was significantly altered by an amount approximately the same as the shoe perturbation, but there was no substantial adaptation in the amount of knee flexion. From the rearfoot patterns it was inferred that time to maximum pronation may be an unreliable variable to describe the pattern of rearfoot motion; the two-phase profile using rearfoot velocity may be more useful. It was concluded that certain subtle sagittal plane kinematic adaptations in timing and velocity patterns did occur at the knee in response to the shoe perturbations.
A device to simulate ankle motion associated with inversion ankle injury was constructed. This device consists of a trap door that can be tilted 30° from the horizontal plane. Surface EMG electrodes were placed over the peroneus brevis and peroneus longus muscles. The time measured from the tilting of the plate to the first muscular response on the EMG was defined as the reflex time. Twenty individuals with unilateral ankle joint instability were tested. The mechanical ankle joint stability was measured using standardized radiographic measurements, taking into account anterior talar translation and talar tilt. The mean anterior talar translation was 5.9 mm and the mean talar tilt was 3.2° in the stable ankles, compared to 12.7 mm and 10.5° for the unstable ankles. The mean reflex time was 68.8 ms (peroneus longus) and 69.2 ms (peroneus brevis) in the stable ankles as compared to 84.5 ms (peroneus longus) and 81.6 ms (peroneus brevis) in the unstable ankles. Important factors influencing functional instability are discussed.
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.
