KINETICS OF THE COMPUTER-SIMULATED TENNIS STROKE WITH DIFFERENT RACKETS

INTRODUCTION: The aim of this biomechanical analysis of the tennis stroke is the determination of the effects of the mass properties of different tennis rackets' on the kinetics of the striking arm. In contrast to experimental investigation the computer simulation gives an infinite temporal resolution so that the arm movements could be investigated especially during the racket-ball-contact phase. The planar model of the tennis stroke consisting of the immovable trunk, the upper arm, the lower arm, the hand and• the racket was derived from the mo ei of the human body by GLITSCH (1993). The striking arm with a racket tightly fixed to the hand was constructed as a pendulum of three rigid bodies which are connected with frictionless revolute joints. An elastic spring (0=45000 N/m) represents the ballracket-contact. The arm-racket-system• rotates around the shoulder joint and hits the resting ball in the respective" racket area centre. Considering rigid body mechanics the mass distributions of three different tennis rackets were measured and served as input for the model. The computer simulation with the initial conditions referring to real tennis strakes registered by KNUDSON (1990) was carried out with the software-packet DADS (Dynamic Analysis and Design System) by CADSI (Computer Aided Design Software Inc.). RESULTS: As it is shown in figure 1 the computer simulation has calculated an elbow flexion when rackets 1 or 2 are used. When the tennis forehand stroke is carried out with racket 3 the elbow is kept extended during the ball-racket-contact phase. The quite different arm movements during the impact with different tennis rackets are the result• of the separate locations of the centres of percussion with respect to the rigid handracket-system. The centre of percussion of racket 3 (5.3 cm) is located more distally than its centre of area because of the different mass distribution and finally because of its greater moment of inertia. In contrast to that the centre of percussion of the other two rackets (racket 1: -3.6 cm, racket 2: -3A cm) are located more proximally than the hitting point. CONCLUSION: The mechanical properties of tennis rackets, particularly the mass distribution, are responsible for different and movements during the ball-racket-contact phase. Obviously, there is no consensus of the preferable mass distribution of modern tennis rackets. This model can objectively assist in choosing one's individual favourable racket. REFERENCES: Glitsch U., Farkas R. (1993): Applications of a multi-body simulation model in human movement studies. Proc. Int. Soc. of Biomech., XIV1h congress, Paris. Knudson, DV (1990): Intrasubject variability of upper extremity angular kinematics on the tennis forehand drive. Int. J. of Sport Biomech., 6, 415-421

PRESSURE DISTRIBUTION UNDER THE FOOT DURING TAKE OFF IN TRAMPOLINING

In the past, biomechanical investigations in trampolining were mostly concerned with the aerial movements, whereas the take off was rarely in the focus of interest. One reason for this lack may be the difficulties in performing dynamic measurements during the take off. The development of new pressure measurement devices encourages their use also in trampolining. At first two questions should be answered with the aid of this instrumentation. 1. Which differences in the pressure distribution occur between beginners and skilled gymnasts? 2. Are there any basic differences in the pressure distribution at take off between exercises with and without moment of impulse? Methods The pressure distribution was determined using F-SCAN, a resistive based in-shoe measurement device. The insole is 0.17 mm thick and contains 960 sensors (resolution 4 sensors/cm2). The sampling rate was 50 Ha and the sampling time embraced 4 s. The sole was cut to the necessary size and put in the right gymnast shoe of the subject. The data transmission ensued via a cuff unit (m = 300 g) and a wire to a personal computer. The investigated movements included three categories of exercises: 1. straight jump, 2. forward sommersaults (single up to double), 3. backward somersaults (single up to double). As subjects sewed 2 female beginners and 5 skilled gymnasts (female and male). Results and Discussion The ratios of support time and flight time confirm the spring characteristic of a trampoline. For one subject the support time is constant and independent from the jump hight. No general differences in the pressure distribution could be found between beginners and skilled subjects. Except the straight jump, it was not possible to distinguish the different somersaults (forward - backward) in terms of pressure distribution by the use of statistical methods. But the intraindividual analysis of the exercises showed a relation between the skill and the variance of the pressure distribution. It can be concluded that the dynamic of the foot contact has always the same characteristic. The moment of impulse is produced by the movements of the upper parts of the body

A STUDY OF THE MECHANICAL ENERGY DIFFERENCES BETWEEN TREADMILL AND OVERGROUND WALKING

The aim of this paper was to analyze the components of the mechanical energy of the body considering the differences between treadmill and overground walking. One subject was filmed while walking at 1.5 m/s on treadmill and overground. The results show that the patterns of the curves are very similar, but the change in the total energy, both in the upper as in the lower extremity were greater on overground (23.20J and 17.47J respectively for overground and treadmill and for the upper extremity 4.91J and 2.56J). The potential energy change of the trunk was also greater on overground (overground 45.97J; treadmill 24.88J). These findings, showing a lower measured mechanical cost on treadmill address the problem whether the treadmill can be used as a valid simulator for overground walking

The Intensive Diet and Exercise for Arthritis (IDEA) trial: design and rationale

Background: Obesity is the most modifiable risk factor, and dietary induced weight loss potentially the best nonpharmacologic intervention to prevent or to slow osteoarthritis (OA) disease progression. We are currently conducting a study to test the hypothesis that intensive weight loss will reduce inflammation and joint loads sufficiently to alter disease progression, either with or without exercise. This article describes the intervention, the empirical evidence to support it, and test-retest reliability data. Methods/Design: This is a prospective, single-blind, randomized controlled trial. The study population consists of 450 overweight and obese (BMI = 27-40.5 kg/m2) older (age greater than or equal to 55 yrs) adults with tibiofemoral osteoarthritis. Participants are randomized to one of three 18-month interventions: intensive dietary restriction-plus-exercise; exercise-only; or intensive dietary restriction-only. The primary aims are to compare the effects of these interventions on inflammatory biomarkers and knee joint loads. Secondary aims will examine the effects of these interventions on function, pain, and mobility; the dose response to weight loss on disease progression; if inflammatory biomarkers and knee joint loads are mediators of the interventions; and the association between quadriceps strength and disease progression. Results: Test-retest reliability results indicated that the ICCs for knee joint load variables were excellent, ranging from 0.86 - 0.98. Knee flexion/extension moments were most affected by BMI, with lower reliability with the highest tertile of BMI. The reliability of the semi-quantitative scoring of the knee joint using MRI exceeded previously reported results, ranging from a low of 0.66 for synovitis to a high of 0.99 for bone marrow lesion size. Discussion: The IDEA trial has the potential to enhance our understanding of the OA disease process, refine weight loss and exercise recommendations in this prevalent disease, and reduce the burden of disability. Originally published BMC Musculoskeletal Disorders, Vol. 10, No. 93, July 200

Epidemiological Evidence for Work Load as a Risk Factor for Osteoarthritis of the Hip: A Systematic Review

Osteoarthritis of the hip (OA) is a common degenerative disorder of the joint cartilage that presents a major public health problem worldwide. While intrinsic risk factors (e.g, body mass and morphology) have been identified, external risk factors are not well understood. In this systematic review, the evidence for workload as a risk factor for hip OA is summarized and used to derive recommendations for prevention and further research.Epidemiological studies on workload or occupation and osteoarthritis of the hip were identified through database and bibliography searches. Using pre-defined quality criteria, 30 studies were selected for critical evaluation; six of these provided quantitative exposure data.Study results were too heterogeneous to develop pooled risk estimates by specific work activities. The weight of evidence favors a graded association between long-term exposure to heavy lifting and risk of hip OA. Long-term exposure to standing at work might also increase the risk of hip OA.It is not possible to estimate a quantitative dose-response relationship between workload and hip OA using existing data, but there is enough evidence available to identify job-related heavy lifting and standing as hazards, and thus to begin developing recommendations for preventing hip OA by limiting the amount and duration of these activities. Future research to identify specific risk factors for work-related hip OA should focus on implementing rigorous study methods with quantitative exposure measures and objective diagnostic criteria

Strength Training for Arthritis Trial (START): design and rationale

Background Muscle loss and fat gain contribute to the disability, pain, and morbidity associated with knee osteoarthritis (OA), and thigh muscle weakness is an independent and modifiable risk factor for it. However, while all published treatment guidelines recommend muscle strengthening exercise to combat loss of muscle mass and strength in knee OA patients, previous strength training studies either used intensities or loads below recommended levels for healthy adults or were generally short, lasting only 6 to 24 weeks. The efficacy of high-intensity strength training in improving OA symptoms, slowing progression, and affecting the underlying mechanisms has not been examined due to the unsubstantiated belief that it might exacerbate symptoms. We hypothesize that in addition to short-term clinical benefits, combining greater duration with high-intensity strength training will alter thigh composition sufficiently to attain long-term reductions in knee-joint forces, lower pain levels, decrease inflammatory cytokines, and slow OA progression. Methods/Design This is an assessor-blind, randomized controlled trial. The study population consists of 372 older (age ≥ 55 yrs) ambulatory, community-dwelling persons with: (1) mild-to-moderate medial tibiofemoral OA (Kellgren-Lawrence (KL) = 2 or 3); (2) knee neutral or varus aligned knee ( -2° valgus ≤ angle ≤ 10° varus); (3) 20 kg.m-2 ≥ BMI ≤ 45 kg.m-2; and (3) no participation in a formal strength-training program for more than 30 minutes per week within the past 6 months. Participants are randomized to one of 3 groups: high-intensity strength training (75-90% 1Repetition Maximum (1RM)); low-intensity strength training (30-40%1RM); or healthy living education. The primary clinical aim is to compare the interventions’ effects on knee pain, and the primary mechanistic aim is to compare their effects on knee-joint compressive forces during walking, a mechanism that affects the OA disease pathway. Secondary aims will compare the interventions’ effects on additional clinical measures of disease severity (e.g., function, mobility); disease progression measured by x-ray; thigh muscle and fat volume, measured by computed tomography (CT); components of thigh muscle function, including hip abductor strength and quadriceps strength, and power; additional measures of knee-joint loading; inflammatory and OA biomarkers; and health-related quality of life. Discussion Test-retest reliability for the thigh CT scan was: total thigh volume, intra-class correlation coefficients (ICC) = 0.99; total fat volume, ICC = 0.99, and total muscle volume, ICC = 0.99. ICC for both isokinetic concentric knee flexion and extension strength was 0.93, and for hip-abductor concentric strength was 0.99. The reliability of our 1RM testing was: leg press, ICC = 0.95; leg curl, ICC = 0.99; and leg extension, ICC = 0.98. Results of this trial will provide critically needed guidance for clinicians in a variety of health professions who prescribe and oversee treatment and prevention of OA-related complications. Given the prevalence and impact of OA and the widespread availability of this intervention, assessing the efficacy of optimal strength training has the potential for immediate and vital clinical impact

A real-time system for biomechanical analysis of human movement and muscle function

Mechanical analysis of movement plays an important role in clinical management of neurological and orthopedic conditions. There has been increasing interest in performing movement analysis in real-time, to provide immediate feedback to both therapist and patient. However, such work to date has been limited to single-joint kinematics and kinetics. Here we present a software system, named human body model (HBM), to compute joint kinematics and kinetics for a full body model with 44 degrees of freedom, in real-time, and to estimate length changes and forces in 300 muscle elements. HBM was used to analyze lower extremity function during gait in 12 able-bodied subjects. Processing speed exceeded 120 samples per second on standard PC hardware. Joint angles and moments were consistent within the group, and consistent with other studies in the literature. Estimated muscle force patterns were consistent among subjects and agreed qualitatively with electromyography, to the extent that can be expected from a biomechanical model. The real-time analysis was integrated into the D-Flow system for development of custom real-time feedback applications and into the gait real-time analysis interactive lab system for gait analysis and gait retraining. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11517-013-1076-z) contains supplementary material, which is available to authorized users