MECHANICAL AND ELECTROMYGRAPHICAL ANALYSIS OF A BOXER'S JAB

INTRODUCTION Very little data exists about the mechanics of maximum force production of a boxeris jab. The purpose of this study was to determine the kinematics and muscular activity during a maximum force jab. Additionally, to determine if differences exist between professional (PRO) and amateurs (AM') boxers during recruitment of both the upper and lower body musculature. METHODS L Four PRO and five AMT boxers (age: 24.2k1.02 yrs; wgt: 81.7+ 8.13 kg; %BF: 11.99+2.6%) volunteered as subjects. Two dimensional kinematic data were collected with a Panasonic AG-500 video camera, operating at 30 Hz. Pre-amplified electrodes were placed on the gastrocnemius (GA), rectus femoris (RF), biceps femoris (BF), external oblique (EO), serratus anterior (SA), pectoralis major-sternal (PEC), anterior deltoid (AD), and tricep brachii (TRI). The EMG data and kinematic data were analyzed with the Ariel Performance Analysis System. Force measures were obtained from an instrumented boxing bag. Subjects performed three trials, after digitizing all trials, the trial with maximum linear velocity at the wrist was selected for further analysis. RESULTS Pearson product-moment correlations were conducted between the force production on the bag and muscle recruitment. The results indicate a significant relationship between force and the BF (r = .47), EO (r = .59) and PEC (r = .60). Tko-sample t-tests were conducted between PRO and AMT force and kinematic data. Significant differences (p < 0.05) were found in force production (t(6) = 2.65), wrist velocity (t(6) = 2.47) and elbow velocity (t(6) = 2.1 1). No significant differences were found between PRO and AMT recruitment of upper and lower body muscles. DISCUSSION The PRO boxers hit the bag harder with increased linear velocity of the wrist and elbow. Although no differences were found in muscle activation between the two groups, the duration and timing of the activation appears to favor the PRO. Because of the relationships found a weight training or resistance training program emphasizing leg extension, abdominal crunches, and shoulder flexion would assist the boxer in production of maximum force. The traditional conditioning program of a boxer (jumping rope, sit-ups, push-ups) would appear to address the boxers needs for both speed and force

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)

Smith-Tant Debate on Campbell\u27s Baptism : Was Alexander Campbell Baptized In Order to Obtain Remission of Sins?

https://digitalcommons.acu.edu/crs_books/1057/thumbnail.jp

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)

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

Large electronic bandwidth in solution-processable pyrene crystals: The role of close-packed crystal structure

We examine the interdependence of structural and electronic properties of two substituted pyrene crystals by means of combined spectroscopic probes and density-functional theory calculations. One derivative features n-hexyl side groups, while the other one contains branched silanyl groups. Both derivatives form triclinic crystal structures when grown from solution, but the electronic dispersion behavior is significantly different due to differences in $\pi$-$\pi$ overlap along the $a$ crystal axis. Both systems display dispersion of 0.40-0.45 eV in the valence band, suggesting a high intrinsic hole mobility. However, the dispersion is primarily along the a-axis in the silanyl-substituted derivative, but less aligned with this crystal axis in the hexyl-substituted material. This is a direct consequence of the diferences in co-facial $\pi$ electron overlap revealed by the crystallographic studies. We find that photophysical defects, ascribed to excimer-like states, point to the importance of localized trap states. Substituted pyrenes are useful model systems to unravel the interplay of crystal structure and electronic properties in organic semiconductors.Comment: 25 pages, 8 figure

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%

1946: Abilene Christian College Bible Lectures - Full Text

Abilene Christian College Lectures - 1946 INTRODUCTION It has been our purpose at Abilene Christian College down through the years to provide in the Annual Bible Lectureship programs that which would be appropriate for the time and most useful to the students and to the Lectureship visitors. The general subject for the 1946 lectures is “Things That Cannot Be Shaken.” This subject was selected because one of the battles, if not the battle, which the church faces today is against those forces which would undermine the bases of gospel truth. Many denominational leaders, in one way or another, are denying even the fundamentals of fundamentals— God is, the Bible is God\u27s Revelation, Jesus Christ is the Son of God and The Kingdom Cannot Be Shaken. Many others, some without knowing what they do, are accepting false teachings and ideologies which, if allowed to run their course, will destroy all true religion. It is believed that the 1946 lectures and this edition of the lectures will help toward establishing in the hearts of men the truth of the important theses discussed. It was the purpose of those who arranged the program that the Lectureship should, also, hold up Christianity as a working, practical religion; hence, the meetings on “Work in New Fields” and “The Church at Work.” The attendance of this Lectureship was the largest in the history of these yearly meetings. On Wednesday evening Brother Nichol spoke to a crowd of approximately 1700 persons. Other evening lectures were attended by crowds almost as large. Visitors came from more than a score of States and, also, from Canada and Mexico. It is the hope of all of us at the College that the fellowship of the 1946 Lectureship and the instruction given by the various speakers will continue to do good for years without end. DON H. MORRIS