JOINT POWER PRODUCTION DURING FLAT AND SLICE TENNIS SERVES

INTRODUCTION Joint power calculations not only are related to muscle force but also provide information on the changes in muscle length and the type of load produced (eccentriclconcentric) (Andrews, 1983; ~inte;, 1990). It was the aim of this study to compute the joint power developed at the wrist, elbow, and shoulder joints during the performance of flat and slice tennis serves. METHODS Five male, right-handed collegiate tennis players were filmed using the DLT method of 3D cinematography. Film analysis procedures and quintic spline functions were used to calculate and to smooth the 3D coordinates of the landmarks, respectively. The following events were defined: ball toss (BAT); maximal elbow flexion (MEF); racket lowest point (RLP), start of forward swing; maximum external rotation (MER); and impact (IMP). Rigid body kinematics and the inverse dynamics approach were used to calculate the resultant torque and force at each joint (Bahamonde, 1994). Joint power (P,) was calculated as the product of the components of the resultant joint torque (T,) and the joint angular velocity (a~()W inter, 1990). RESULTS Table 1. Average Joint Power (Watts) Values for the Flat and Slice Serves CONCLUSIONS Large eccentric loads (pre-stretching) were placed on the internal rotator muscles during the late portion of the backswing and the early forward swing; changing into concentric loads prior to IMP. Elbow loads (extension and pronation) were concentric throughout the forward swing. Wrist concentric (flexion and ulnar deviation) loads increased in magnitude near impact (MERAMP). In general, the magnitude of the joint power values were larger for the flat serves than for the slice serves. The joint power needed to accelerate the racket was the result of shoulder internal rotation, elbow extension and pronation, and wrist flexion and ulnar deviation. REFERENCES Bahamonde R. (1994) Biomechanical Analysis of the Serving Arm During the Performance of Flat and Slice Tennis Serves. Doctoral Dissertation, Indiana University. Andrews, J. (1983) Biomechanical Measures of Muscular Effort. Med. Sci. Sport. Exer., 15(3),199-207. Winter, D.A. (1990) Biomechanics and Motor Control of Human Movement. Wiley & Sons, New York

KINEMATIC ANALYSIS OF THE TRADITIONAL BACK SQUAT AND SMITH MACHINE SQUAT EXERCISES

The purpose of this study was to compare the kinematics of the traditional back squat (TBS) and the Smith Machine Squat (SMS). The squat exercise is a common exercise in strength and conditioning programs as well as in rehabilitation settings. Eight experienced college age weight lifters performed both TBS and SMS. Three dimensional video analyses were used to analyze the motions. Lower extremity joints and trunk angular motions were computed and compared using Paired T-test. The TBS generated larger ROM than the SMS in all the joints measured. Due to the linear restriction of the bar motion along the vertical axis in the SMS the subjects positioned their feet forward to enable bar lowering. This feet placement positioned the bar farther away from the knee at the instance of maximal knee flexion

EFFECTS OF GENDER AND THE LEWIS FORMULA IN MECHANICAL POWER ESTIMATES

One of the simplest way to calculate power-output is using the Lewis formula. Harman et al. (1991) and Garhammer (1993) stated that the Lewis formula is not scientifically correct but it still widely used. Only a limited number of studies have tried to determine if there is a need for separate power-output prediction equations for each gender (Mayhew & Salm, 1990; Garhammer, 1993). The purpose of this study was to determine the need of separate power-output prediction equations for each gender and to test the validity of Lewis formula in the prediction of power output. Forty-nine female and 69 male athletes were measured for height, weight, thigh circumference, thigh skinfold, thigh length, and foreleg length. The athletes performed a countermovement jump and reach test from a force platform. A Vertec jumping apparatus was used to measure vertical jump height 0an d the force platform was used to acquire force-time data to determine actual peak and average power output. Eight anthropometric measurements, VHJ, and gender were used in a stepwise multiple regression statistical procedure to develop the prediction equations. One way ANOVA with repeated measures was used to compare the predicted average power from the Lewis formula, the estimated average power values developed in this study, and the actual average power values measured. There were significant differences (

SHOCK ABSORPTION CHARACTERISTICS OF FOOTWEAR WORN BY AEROBIC INSTRUCTORS

Aerobic exercise is one of the most popular forms of cardiovascular exercise among women. Numerous studies have documented the high incident of lower extremity injury among aerobics instructors. Factors contributing to the high incidence of injuries include, type of floor, overuse, falls and shoes. Aerobic instructors have identified their shoes as the second possible cause of injuries (Davis and Bahamonde, 2000). Eleven aerobic instructors were given two popular brand name of aerobic shoes. The shock absorption of the shoes were tested after a determined number of hours of use. Tests were done at heel and toe box and with and without the insole

COMPARISON OF TWO METHODS OF MANUAL DIGITIZATION ON ACCURACY AND TIME OF COMPLETION

The purpose of this study was to compare the accuracy and time efficacy of two methods of manual digitization (frame by frame, FXF and points over frame, POF). Two groups (experienced, N=20 and inexperience, N= 20) digitized markers using the FXF and POF method. The markers were digitized automatically using software HUMAN and the coordinates from the automatic digitizing were the true values and the manually digitized values were the measured values. These coordinates were used to compute an average root mean square (RMS) value for each subject. An ANOVA (Group x Method) was used to analyze the difference between digitizing time and RMS values. The POF method was more accurate than the FXF method in all of the landmarks analyzed. The advantage of the POF method lies in the ability of the subjects to continuously track the same point throughout the trial

Antitrust compliance

Insistindo um pouco no que já foi aqui referido, o Compliance deve ser encarado como uma prática de conformidade, i.e., como um sistema cujo último propósito consiste na obtenção do maior grau de convergência entre o comportamento de uma organização, lato senso, e o conjunto de normas que lhe são aplicáveis.info:eu-repo/semantics/acceptedVersio

Holographic complexity for time-dependent backgrounds

In this paper, we will analyze the holographic complexity for time-dependent asymptotically AdS geometries. We will first use a covariant zero mean curvature slicing of the time-dependent bulk geometries, and then use this co-dimension one spacelike slice of the bulk spacetime to define a co-dimension two minimal surface. The time-dependent holographic complexity will be defined using the volume enclosed by this minimal surface. This time-dependent holographic complexity will reduce to the usual holographic complexity for static geometries. We will analyze the time-dependence as a perturbation of the asymptotically AdS geometries. Thus, we will obtain time-dependent asymptotically AdS geometries, and we will calculate the holographic complexity for such time-dependent geometries

Genetical genomics: use all data

BACKGROUND: Genetical genomics is a very powerful tool to elucidate the basis of complex traits and disease susceptibility. Despite its relevance, however, statistical modeling of expression quantitative trait loci (eQTL) has not received the attention it deserves. Based on two reasonable assertions (i) a good model should consider all available variables as potential effects, and (ii) gene expressions are highly interconnected, we suggest that an eQTL model should consider the rest of expression levels as potential regressors, in addition to the markers. RESULTS: It is shown that power can be increased with this strategy. We also show, using classical statistical and support vector machines techniques in a reanalysis of public data, that the external transcripts, i.e., transcripts other than the one being analysed, explain on average much more variability than the markers themselves. The presence of eQTL hotspots is reassessed in the light of these results. CONCLUSION: Model choice is a critical yet neglected issue in genetical genomics studies. Although we are far from having a general strategy for model choice in this area, we can at least propose that any transcript level is scanned not only for the markers genotyped but also for the rest of gene expression levels. Some sort of stepwise regression strategy can be used to select the final model

QUALITATIVE BIOMECHANICS FOR COACHING

Session Information: Coaches must apply principles of biomechanics in their qualitative judgments of the technique used by athletes. These judgments can have a major influence on performance and injury risk. This session will focus on the most effective use of qualitative biomechanical analyses and video replay software. Several scholars who have experience teaching qualitative biomechanical analysis to future coaches will present, followed by a question and answer session. Schedule of Presentations: Dr. Knudson will introduce the session and provide a brief overview of qualitative biomechanical analysis. 11:00 – 11:15 Dr. Alderson will present sport injury models as they apply to assessment, intervention and rehabilitation of common injuries in cricket, tennis and running. Relevant qualitative and quantitative 2D features of SiliconCoach that can be utilised by a coach to potentially reduce injury incidence will be presented. 11:15 – 11:45 Dr. Bahamonde will present how qualitative analysis can be used to teach biomechanics concepts to physical education and coaching students. Movement examples from tennis, soccer and track field and meaningful features of Hu-m-an software will be illustrated. Hu-m-an is unique in that it was developed with a specific teaching-learning focus. 11:45 – 12:15 Dr. Bird will present biomechanical core concepts as a “common language” to evaluate and improve all human movements. The core concepts are visually observable, but meaningful features of Dartfish will be illustrated to enhance what is seen by both the coach and the mover. Movement examples from golf, resistance training, basketball, and other sports will be presented. 12:15 – 12:45 Discussion: 12:45 – 13:00 This will provide an opportunity for delegates to ask specific questions relating to any of the presenters