MATCHING TECHNOLOGY TO COACHING NEEDS

The biomechanist uses sophisticated and expensive instrumentation to produce quantitative data in the area of sport technique. The coach uses the naked eye to provide a qualitative description of a particular sport movement. Excellent research on sport technique is published in refereed journals but not modified to assist the coach in its interpretation. Technique errors in the coaching literature indicate a need to disseminate the research data in a format in which the coach may use to help the performer. A coach with a solid understanding of the biomechanical basis of a particular skill and the ability to evaluate that skill can modify the technique for maximum benefit and reduction of injury. If the biomechanist and coach are going to communicate for the benefit of the performer, a number of concerns must be addressed. First, the biomechanist must be willing to translate the acquired research findings into appropriate terminology for the coach to understand. Secondly, the coach must be willing to learn new and more effective ways for producing successful results. Lastly, all parties concerned must use this acquired knowledge for the benefit of the performer. Several successful cooperative programs have appeared in the past several years. Miller (1993) presented the use of analysis software with instructional modules to assist the coach with understanding the mechanics of motion. Smith and Spinks (1989) developed an on-water data collection system to provide immediate feedback to the coach to determine flaws in force production of the rower. Jarvis and Marshall ( 1987) used data from a single and double flyaway from the high bar for a simulation procedure that predicted the variations in biomechanical parameters at release and in flight that must occur for a triple somersault to be performed. Tant and Wilkerson (1989) found that extremely large ground reaction forces of young gymnast landings could be reduced if the subject was able to see the results on a computer screen. Biomechanists have already been providing ways to enhance technique development, reduce stress placed on the body, and design equipment for the individual performer. However, if we as biomechanists are to be a viable force in athletic endeavours we must share the results and work together with the coach so performance at all levels, from the elite to the disabled, can be improved

KINETIC AND KINEMATIC CHARACTERISTICS OF IMPACTS FROM VARIOUS HEIGHTS EXPERIENCED BY CHILDREN

In 1977, the United States Consumer Product Safety Commission reported treatment of93,000 children in emergency rooms for injuries sustained on playgrounds. By 1986, the number had risen to over 200,000 and 70 percent ofthese cases were falls from equipment onto various play surfaces (U.S. Consumer Product Safety Commission, 1986). In addition to free play activities, today's youth are also experiencing acute injuries from single impact trauma during organized sports (Micheli, 1986)

AN ANALYSIS OF THE ERGOMETER AND RECUMBENT CYCLES IN TWO DIFFERENT SEAT POSITIONS

INTRODUCTION The bicycle ergometer has been used as a fitess and rehabilitative tool by many individuals. The recumbent bicycle, a relatively new ergometer, is also being used in this capacity. Although there has been a surge in research on the stationary bicycle, the majority of it has been oriented toward fitness rather than rehabilitation. Ericson, Nisell. and Gunner (1988) suggest that the bicycle is an useful therapeutic device because it increases range of motion (ROM) at the hip, knee and ankle joints and reduces compressive forces on the lower body. Mechanical loads placed on different joint structures can be controlled by changes in the workload, pedaling rate, or seat position of the ergometer. Timmer (1991) found that increased seat height produced greater ROM with increased stress on the anterior cruciate ligament of the knee but, decreased seat height reduced patellofemoral pressure and compressive forces at the tibiofemoral joint. There is no doubt that the exercise cycle is becoming more widely used, but the protocols for its use in rehabilitation have not been tested. Thus, the purpose of this study was to compare the kinematic and kinetic variables of the lower body, during the cycling motion, on two different cycles at two different seat positions. Additionally, to determine if specific cycles may produce unwanted stresses on the lower body during the rehabilitation process

MECHANICAL MODEL FOR DETERMINING BASE RUNNING SPEED OF SOFTBALL PLAYERS

INTRODUCT10N -Speed on the bases is critical for fast pitch softball players. A mechanical model of critical features contributing to this speed is important for both the coach and athlete for success. The purpose of this study was to develop a model and determine which variables the coach could manipulate to enhance the success of the players. METHODS• Hat (1993) proposed a deterministic model for sprinting. Average speed was determined by stride length (SL) and stride frequency (SF). SL was further divided into takeoff distance, flight distance, and landing distance with mechanical variables which contribute to these distances supporting SL. SF was also further divided into stride time and additional mechanical variables. Our model incorporated these variables and included variables related to the physical characteristics of the subjects which could be manipulated by the athlete coach. Thirty-nine female NAIA and Division 11 softball players served as subjects. RESULTS -A database was created to determine the demographics of the population selected and of the preliminary data for the proposed model. The data in the table 00low represents the demographics of the population. The data were used 10 support our model and develop a practical approach to enhancing speed of a softball player. Hay, J.G. (1993). The Biomechanics of Sport Techniques. New Jersey: PrenliceHall, pp. 396-422 (Track and fjeld: Running)

MECHANICAL VARIABLES OF JUMPING DURING NAVAL ACADEMY OBSTACLE COURSE TRAINING ACTIVITIES

Introduction•-The use of the obstacle course (O-course) activities at the U.S. Naval Academy is mandatory for all midshipmen. To reduce injuries on the 0course, research has been conducted to evaluate other methods related to specific work assignments. The purpose of this study was to determine which variables contributed to the successful jump used in jumping to clear a shelf. METHODS -Five males (age: 20.2 yrs ±1.3; hgt: 178.6 cm± 3,7; wgt: 77.4 kg±7.7) and five females (age: 20.0 yrs ±1.9; hgt: 170.64 cm±7.3; wgt: 63.8 kg ± 8.5) served as subjects. Anthropometric, strength, and video data were collected at the U.S. Naval Academy, Annapolis MD. Three-dimensional video images were collected from the sagittal and posterior views as subjects scaled a shelf. Fifteen data points were digitized, files transformed, data smoothed with a digital filter set at 10Hz and graphed with the Ariel Performance Analysis System (APAS). RESULTS -Statistical differences using two-sample t-tests were found between males and females in the variables: hgt (t=2.193); wgt (t=2.639); percent body fat (t=5.028); leg length (t=2.128); knee flexion peak torque % BW(t=4.459); knee extension peak % BW (t=2.128); knee flexion (t=1.937); and hip extension (t=3.207). All subjects cleared the shelf. However, several subjects used additional time to complete the skilI. Because differences were noted in anthropometric, strength, and kinematic variables, the skill of jumping to c1eartheshelfseemsto favor the taller, stronger individuals. CONCLUSIONS -Because the Navy is incorporating gender neutral standards into their physical training standards, the 0course may not be the most appropriate way of measuring these standards

FACTORS CONTRIBUTING TO SOFTBALL PLAYERS BASE RUNNING SPEED

INTRODUCTION • The fast pitch softball player relies on speed to reach a base successfully. The purpose of this study was to determine the mechanical variables which contribute to the success of the player on the base paths. METHODS -Thirty-nine female NAIA and Division 11 softball players served as subjects. Subjects were tested with a battery attests based on the theoretical model proposed earlier. Subjects were also videotaped in the sagittal view running from home plate to first base. The video images were captured, transformed, smoothed, and graphed with the Arie! Performance Analysis System (APAS). Data were statistically determined with regression analysis to determine which variables would predict speed. RESULTS • The dependent variable was fly 40 time and the independent variables age, wgt, hgt, percent body fat, sit and reach, sit-ups, leg press, stat 40 times, stride length. cog displacement x, trunk inc1ination, and angular displacement at the hip, knee, and ankle. The demographie data were presented previously. The kinematic data are displayed in the table below The variable with the highest regression coefficient to the fly 40 times was leg press (r=.8692). Stat 40 time was highly correlated to fly 40 times (r=.7354). CONCLUSIONS• The kinematic variables selected did not aid in the prediction process. Because of this the model may be revised and/or different variables selected for interpretation

SEGMENTALCOORDINATIONAND TEMPORAL STRUCTURE OF THE VOLLEYBALL PIKE

In the game ofvol1eyball, the spike is one ofthe most difficult and demanding techniques to master. The athlete is expect4ed to jump and hit a ball with maximum force and accuracy at the approximate peak of the jump. Prsala (1982) identified four phases in the analysis of the spike: the approach, preparation, hitting, and landing. The approach involves t 0 or three controlled running strides, a transitional last step to prepare for the transfer ofhorizontal momentum to vertical momentum, and a two foot vertical jump. In the preparatory phase the striking arm is swung upward in an abduct d and laterally rotated position. The elbow is fle ed at approximately 90 degrees and the wrist hyperextended. During the hitting phase, the shoulder is elevated; the upper arm is inwardly rotated and a ducted; the forearm is extended at the elbow and the wrist is flexed. The athl te absorbs the downward momentum by flexing the joints of the lower extremities when landing

A spectral method for sizing cracks using ultrasonic arrays

Ultrasonic phased array systems are becoming increasingly popular as tools for the inspection of safety-critical structures within the non-destructive testing industry. The datasets captured by these arrays can be used to image the internal structure of individual components, allowing the location and nature of any defects to be deduced. Although there exist strict procedures for measuring defects via these imaging algorithms, sizing flaws which are smaller than two wavelengths in diameter can prove problematic and the choice of threshold at which the defect measurements are made can introduce an aspect of subjectivity. This paper puts forward a completely objective approach specific to cracks based on the Kirchhoff scattering model and the approximation of the resulting scattering matrices by Toeplitz matrices. A mathematical expression relating the crack size to the maximum eigenvalue of the associated scattering matrix is derived. Analysis of this approximation shows that the method will provide a unique crack size for a given maximum eigenvalue whilst providing a quick calculation method which avoids the need to numerically generate model scattering matrices (the computation time is up to 10^3 times faster). A sensitivity analysis demonstrates that the method is most effective for sizing defects that are commensurate with or smaller than the wavelength of the ultrasonic wave. The method is applied to simulated FMC data arising from finite element calculations where the crack length to wavelength ratios range between 0.6 and 1.9. The recovered objective crack size exhibits an error of 12%

Influence of the Surface Properties of the Bois Carre Seeds Activated Carbon for the Removal of Lead From Aqueous Ssolutions

An activated carbon from Bois carré (Citharexylum Fruticosum L.) seeds was prepared by chemical activation with phosphoric acid. The activated carbon obtained has a surface area of 594 m2/g and a high content of acid groups of 3.44 mmol.g-1. This carbon was studied for the removal of lead from water. Sorption studies were performed at 30 °C at different pH and adsorbent doses, in batch mode. Maximum adsorption occurred at pH 7 for an adsorbent dose of 1g/L. Kinetic studies, at the initial concentration of 150 mg/L of lead, pH 5 and an adsorbent dose of 1 g/L, yielded an equilibrium time of 30 h for this activated carbon. The kinetic data were modelled with the pseudo first order, the pseudo second order and the Bangham models. The pseudo second order model fitted the data well. The sorption rate constant (2.10-3 mol-1.Kg.s-1) and the maximum amount of lead adsorbed are quite good (0.18 mol.kg-1) compared to the data found in literature. Sorption equilibrium studies were conducted in a concentration range of lead from 0 to 150 mg/L, at pH 5, adsorbent dose 1 g/L. In an aqueous lead solution with an initial concentration of 30 mg/L, activated Bois carré seed carbon removed (at equilibrium) 48 % of the heavy metal. The equilibrium data were modelled with the Langmuir and Freundlich equations, of which the latter gave the best fit. The Freundlich constants n (3.76 L.mol-1) and Kf (1.06 mol.kg-1) are in good agreement with literature. The Bois carré seed activated carbon is a very efficient carbon in terms of the metal amount adsorbed per unit of surface area (0. 06 m2 /g). This good result is due to the presence of many active acid sites on the surface of this activated carbon