MEASUREMENT AND EVALUATION OF LOADS ON THE HUMAN BODY DURING SPORTS ACTIVITIES

Introduction: Mechanical loads on the human body are necessary to stimulate bone growth, to maintain bone integrity, and to strengthen the skeletal musculature. However, excessive forces, repetitive shock and high pressures have been identified as contributors to traumatic and overuse injuries. For events of short duration, cinematographic techniques are normally not sufficient to estimate the forces and accelerations experienced by the body's center of mass (CoM) or any one of its parts. Therefore, mechanical sensors are necessary to register forces, accelerations and pressure distributions that occur during sports activities. This methodological overview concentrates on technological aspects and the application of force, pressure and acceleration measurements. Methods: In the field of biomechanics piezoelectric and strain gage force platforms are commonly used for the determination of ground reaction forces. Properly mounted, these measuring devices provide high accuracy and a good frequency response. Desirable transducer characteristics for biomechanical applications may differ from characteristics advantageous for engineering usage. Measurement of pressure during sitting or lying on a bed requires a soft and pliable transducer mat that will adapt to the shape of the human body. However, such a transducer will not show good technical specifications. In recent years pressure distribution sensors have been developed using conductive paint as well as capacitive and piezoelectric transducers. Compared to force platforms, pressure distribution sensors allow a much more detailed analysis of the mechanical interaction of the human body with the ground. Pressure devices generally demonstrate reduced accuracy and lower frequency responses as compared to traditional force platforms. Strain gage, inductive, and piezoelectric technologies are also applied for the construction of accelerometers. They are important for the measurements of shock and vibrations at various parts of the body. Skin motion is a major problem for acceleration measurements in biomechanics, and care should be taken to minimize these artifacts. Applications: The use and the limitations of ground reaction force measurements will be demonstrated for locomotor and other athletic activities. In-shoe pressure distribution techniques have proven valuable in product testing of athletic footwear. Differences between shoes can easily be detected and the aging of material with use can be tested. The substantial influence of skin motion on acceleration measurements will be demonstrated, and methods will be suggested to reduce these skin artifacts. Running and tennis will be chosen as examples to demonstrate the use of acceleration measurements

BIOMECHANICAL EVALUATION OF RUNNING AND SOCCER SHOES: METHODOLOGY AND TESTING PROCEDURES

Running shoes are the footwear, that has been explored the most by scientists in the field of biomechanics. Following the running shoe research peak between 1980 and 1990 other products became the focus of interest. In particular, many shoe studies were performed in the field of basketball and other indoor sports. Only recently, soccer boots have received a lot of attention and were explored by various research groups. Other than in running shoes, soccer boots have additional tasks to perform. These shoes are used for kicking, they should provide sufficient traction for rapid cutting manoeuvres and assist the players in rapid acceleration and stopping movements. Especially, the often conflicting demands of injury prevention and high performance properties remain to be solved. Test methods for athletic footwear as well as research results will be presented here. This will demonstrate how important biomechanics has become in providing the necessary knowledge for the design of functional footwear

A METHOD TO DETERMINE BALL IMPACT LOCATION AND ITS MOVEMENT ACROSS THE STRINGS OF A TENNIS RACKET

INTRODUCTION: The impact location of a ball on the string plane area of a given tennis racket and its movement across the strings influences ball speed, direction of flight, and the resulting spin of the ball. The accuracy and resolution of cinematographic recordings are limited because the racket head area is small in comparison to the necessary object space for filming. Because the interaction of the tennis racket with the ball is of fundamental importance for the game, an instrumented tennis racket was developed to electronically determine the point of ball impact on the strings. METHODS: A “Kuebler Inertial Light" tennis racket was used for this study. 32 very thin steel wires were woven around 14 longitudinal and 18 transverse string sections of the racket head. This resulted in a 14 by 18 wire matrix, covering a large area of the racket head. Each steel wire was electrically insulated and connected to a charge amplifier by a thin, shielded cable. The thin cable bundle from the 32 sensors ran along the racket handle to a small electronic unit, which was attached to a belt and carried by the subjects. Total racket weight was increased slightly by the wires, but was still well within the range of weights found in commercially available tennis rackets. Through its friction with the ground and during its flight through the air, the tennis ball was electrically charged before it made contact with the racket head. At ball contact, an electrostatic charge was detected by the steel wires and electronically processed by their charge amplifiers. Using a data acquisition system with a high sampling frequency, each wire was sampled with 5 kHz. In a pre-trigger mode, data were collected for a total of 12 ms, beginning 4 ms before initial charge detection by the sensors. Following data collection, further mathematical processing was performed by multiplying the charge values of each of the longitudinal sensors with all transverse sensors, resulting in a 14 by 18 matrix of numbers. Geometric averaging of all matrix values determined the point of contact on the string area. RESULTS AND CONCLUSIONS: According to the judgment of experienced tennis players, the handling of the instrumented racket was very similar to a regular racket for forehand and backhand strokes, as well as for the serve. Only for topspin and slice strokes was a slightly increased spin production on the ball recognized. Subjects felt comfortable with the racket, some of them achieving ball speeds over 190 km/h for their serves. The matrix sensor arrangement and the time resolution of 0.2 ms guaranteed an accurate determination of the contact location of the ball and its movement across the string area. From these data, ball movements on the racket head can be shown for typical examples of forehand, backhand, topspin and slice strokes, as well as for serves

BALL IMPACT LOCATION ON A TENNIS RACKET HEAD AND ITS INFLUENCE ON BALL SPEED, ARM SHOCK AND VIBRATION

INTRODUCTION: Brody (1988) defined 3 different ‘sweet spots’ on the strings of a tennis racket. When a ball hits the racket at its point of maximum restitution (CoR), the rebound velocity of the ball will be highest. For ball hits at the node of the racket, vibrations are minimal. Ball contacts at the center of percussion (CoP) cause minimal shocks to the arm. The definitions of these points are based on the application of the laws of physics to a simple mechanical body - the tennis racket only. In a real game situation, however, tennis rackets are not simple and well-defined mechanical bodies. The player’s muscle actions continuously modify the grip forces at the racket handle. Therefore, mechanical coupling of the racket handle with the body is changed with each modification of grip force, resulting in a complex mechanical behavior of the racket-arm system. Using a game-like situation, this study investigated the influence of ball impact location on the racket head on ball velocity, arm shock and vibration. METHODS: Each of 19 expert tennis players performed 30 fore- and backhand strokes and 30 straight serves. A “Kuebler Intertial Light” tennis racket was instrumented to determine the ball contact and its movement across the racket head (Hennig & Schnabel, 1998). For the measurement of shock and vibration from the racket to the arm an accelerometer was fastened to the wrist (Proc. styloideus ulnae). Ball velocity was measured by a photocell arrangement. To determine relationships between the variables, simple and multiple regression analyses were performed. RESULTS AND CONCLUSIONS: Although all subjects belonged to a group of expert players with a similar level of performance, the patterns of ball contact were quite different between players. However, independent of each player’s individual technique, minima of arm shock and vibration were identified at impact locations, closer to the racket handle than those proposed by Brody (1988) as CoP and node. Using individual analyses across the 30 repetitive trials of each player, high multiple regression coefficients were found between ball contact points and roll distance on the strings, loads on the arm, ball velocity and contact time. REFERENCES: Brody, H. (1988). Tennis science for tennis players, 4th ed. Philadelphia: Univ. of Pennsylvania Press. Hennig, E., & Schnabel, G. (1998). A method to determine ball impact location and its movement across the strings of a tennis racket. In ISBS Proceedings, Konstanz, Germany

GROUND REACTION FORCES, REARFOOT MOTION AND WRIST ACCELERATION IN NORDIC WALKING

The aim of this study was to analyze loading parameters in nordic walking (NW) compared to ordinary walking (W) with respect to upper and lower limb injury risks. 24 licensed NW-instructors, 12 male and 12 female (38±13 years, 175±9 cm, 78±14 kg, BMI 25±3 kg/m2), performed W and NW trials on a runway covered with artificial turf. Walking speed was controlled by two photo cells. By using an electrogoniometer and a Kistler platform, pronation and ground reaction forces were measured. Wrist acceleration was quantified by an uniaxial accelerometer attached to processus styloideus radii of the right forearm. Statistical evaluation was done by ANOVA and post hoc t-tests (

CHILDREN’S PLANTAR PRESSURE DISTRIBUTION MEASUREMENTS: INFLUENCE OF FOOTWEAR

INTRODUCTION: Several significant studies (Aharonson et al., 1989; Orlin et al., 1990; Hennig & Rosenbaum, 1991; Pisciotta et al., 1994) have increased interest in plantar pressure distribution parameters in childhood. All over the world the gait labs, with their ongoing research studies on gait kinetics, are beginning to look for pressure distribution values, as for example Bontrager et al. (1997). More than a hundred years ago, Marey in 1886 and Beeley in 1882 developed plantar pressure measurement techniques. These techniques have continued to be developed, and at present there are measurement systems based on such different principles as footprints, optical, acoustical, pneumatic, hydraulic, inductive, piezoelectric, capacitive and resistive. (Borges Machado, 1994

Plantar Pressure Distribution Patterns During Gait in Diabetic Neuropathy Patients with a History of Foot Ulcers

OBJECTIVE: To investigate and compare the influence of a previous history of foot ulcers on plantar pressure variables during gait of patients with diabetic neuropathy. INTRODUCTION: Foot ulcers may be an indicator of worsening diabetic neuropathy. However, the behavior of plantar pressure patterns over time and during the progression of neuropathy, especially in patients who have a clinical history of foot ulcers, is still unclear. METHODS: Subjects were divided into the following groups: control group, 20 subjects; diabetic neuropathy patients without foot ulcers, 17 subjects; and diabetic neuropathy patients with at least one healed foot ulcer within the last year, 10 subjects. Plantar pressure distribution was recorded during barefoot gait using the Pedar-X system. RESULTS: Neuropathic subjects from both the diabetic neuropathy and DNU groups showed higher plantar pressure than control subjects. At midfoot, the peak pressure was significantly different among all groups: control group (139.4±76.4 kPa), diabetic neuropathy (205.3±118.6 kPa) and DNU (290.7±151.5 kPa) (p=0.008). The pressure-time integral was significantly higher in the ulcerated neuropathic groups at midfoot (CG: 37.3±11.4 kPa.s; DN: 43.3±9.1 kPa.s; DNU: 68.7±36.5 kPa.s; p=0.002) and rearfoot (CG: 83.3±21.2 kPa.s; DN: 94.9±29.4 kPa.s; DNU: 102.5±37.9 kPa.s; p=0.048). CONCLUSION: A history of foot ulcers in the clinical history of diabetic neuropathy subjects influenced plantar pressure distribution, resulting in an increased load under the midfoot and rearfoot and an increase in the variability of plantar pressure during barefoot gait. The progression of diabetic neuropathy was not found to influence plantar pressure distribution

Dietary protein restriction throughout intrauterine and postnatal life results in potentially beneficial myocardial tissue remodeling in the adult mouse heart

Diet composition impacts metabolic and cardiovascular health with high caloric diets contributing to obesity related disorders. Dietary interventions such as caloric restriction exert beneficial effects in the cardiovascular system, but alteration of which specific nutrient is responsible is less clear. This study investigates the effects of a low protein diet (LPD) on morphology, tissue composition and function of the neonatal and adult mouse heart. Mice were subjected to LPD (8.8% protein) or standard protein diet (SPD, 22% protein) throughout intrauterine and postnatal life. At birth LPD female but not male offspring exhibit reduced body weight whereas heart weight was unchanged in both sexes. Cardiomyocyte cross sectional area was increased in newborn LPD females compared to SPD, whereas proliferation, cellular tissue composition and vascularization were unaffected. Adult female mice on LPD exhibit reduced body weight but normal heart weight compared to SPD controls. Echocardiography revealed normal left ventricular contractility in LPD animals. Histology showed reduced interstitial fibrosis, lower cardiomyocyte volume and elevated numbers of cardiomyocyte and non-myocyte nuclei per tissue area in adult LPD versus SPD myocardium. Furthermore, capillary density was increased in LPD hearts. In conclusion, pre- and postnatal dietary protein restriction in mice causes a potentially beneficial myocardial remodeling

The relationship between basal and acute HPA axis activity and aggressive behavior in adults

The hypothalamic–pituitary–adrenal (HPA) axis seems to play a major role in the development, elicitation, and enhancement of aggressive behavior in animals. Increasing evidence suggests that this is also true for humans. However, most human research on the role of the HPA axis in aggression has been focusing on highly aggressive children and adolescent clinical samples. Here, we report on a study of the role of basal and acute HPA axis activity in a sample of 20 healthy male and female adults. We used the Taylor Aggression Paradigm to induce and measure aggression. We assessed the cortisol awakening response as a trait measure of basal HPA axis activity. Salivary free cortisol measures for the cortisol awakening response were obtained on three consecutive weekdays immediately following awakening and 30, 45, and 60 min after. Half of the subjects were provoked with the Taylor Aggression Paradigm to behave aggressively; the other half was not provoked. Acute HPA axis activity was measured four times, once before and three times after the induction of aggression. Basal cortisol levels were significantly and negatively related to aggressive behavior in the provoked group and explained 67% of the behavioral variance. Cortisol levels following the induction of aggression were significantly higher in the provoked group when baseline levels were taken into account. The data implicate that the HPA axis is not only relevant to the expression of aggressive behavior in clinical groups, but also to a large extent in healthy ones